Chronic stress adaptation of the nitric oxide synthases and IL-1ß levels in brain structures and hypothalamic-pituitary-adrenal axis activity induced by homotypic stress.

The aim of this study was to determine the effect of repeated restraint stress (RS) on a single restraint (homotypic) stress-induced expression of interleukin-1ß (IL-1ß), neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in the prefrontal cortex (PFC), hippocampus and hypothalamus and their adaptational changes in chronic stress. Also the involvement of plasma IL-1ß in adrenocorticotropic hormone (ACTH) and corticosterone secretion during chronic stress was investigated. Rats were subjected to a single restraint for 10 minutes or restrained twice a day for 3, 7 and 14 consecutive days and 24 hours after the last stress period rats were restrained for 10 min and rapidly decapitated 0, 1, 2 and 3 hours later. The IL-1ß, nNOS and iNOS protein levels in brain structures samples were analyzed by Western blot procedure and IL-1ß, ACTH and corticosterone levels were determined in plasma. Single restraint induced a strongest decrease of iNOS protein levels (1-3 h) in the PFC and a weaker decline in the hippocampus and hypothalamus (3 h) after stress cessation. Single restraint markedly increased IL-1ß protein level in PFC and hippocampus. In the PFC repeated restraint for 3 days significantly increased the homotypic stress induced iNOS and IL-1ß protein levels and this increase gradually declined after 7 and 14 days of repeated restraint. Much weaker yet a parallel changes appeared with neuronal NOS level. In the hippocampus prior stress for 3, 7 and 14 days significantly increased the homotypic stress induced iNOS protein level parallel with IL-1ß level which gradually declined with prolonged period of repeated restraint. In the hippocampus a longer restraint period, 7 and 14 days markedly decreased nNOS protein level evoked by homotypic stress. In the hypothalamus prior stress for 3 days strongly enhanced the homotypic stress-induced iNOS level and repeated stress for 7 and 14 days blunted this effect. Repeated stress increased IL-1ß level in response to homotypic stress after 3 days and after 14 days. The present results indicate time-related similarities in the potent alterations in IL-1ß and iNOS protein levels in brain structures. Single restraint induced a significant increase of plasma IL-1ß level which was abolished by pretreatment with IL-1 receptor antagonist (IL-1Ra). A parallel strong increase of plasma ACTH and corticosterone levels were significantly impaired by IL-1Ra suggesting a marked involvement of stress-induced stimulation of ACTH and corticosterone by IL-1ß in single restraint. In repeatedly restrained rats IL-1Ra significantly blunted plasma IL-1ß level induced by homotypic stress. A parallel strong increase in plasma ACTH level by homotypic stress was not substantially altered by pretreatment with IL-1Ra in repeatedly stressed rats. Plasma a corticosterone level increased by homotypic stress in rats restrained for 3 and 14 days was not affected by pretreatment with IL-1Ra, but after for 7 days its level was significantly enhanced. These results suggest that repeated stress desensitizes IL-1ß-induced stimulatory component in a single restraint stress-induced hypothalamic-pituitary-adrenal (HPA) axis stimulation. A sensitization by homotypic stress of corticosterone response after restraint for 7 days may depend on other stimulatory systems acting within adrenal glands during prolonged stress. Comparative data from the same model of rather mild psychological stress allows for the comparison of functional adaptive changes of NO synthases and IL-1ß in brain structures involved in stress regulation. In general, the iNOS system is strongly sensitized by repeated stress for 3 days in prefrontal cortex and hippocampus. Increased plasma IL-1ß level by a single restraint stress is significantly involved in ACTH and corticosterone secretion. Repeated stress for 3-14 days reduces this participation of IL-1ß in pituitary-adrenal stimulation.

Prostaglandins and interleukin-1beta in the hypothalamic-pituitary-adrenal response to systemic phenylephrine under basal and stress conditions.

We investigated the role of interleukin-1beta (IL-1beta) and prostaglandins (PG) in the alpha(1)-adrenergic agonist, phenylephrine-induced hypothalamic-pituitary-adrenal axis (HPA) responses under basal and social stress conditions. Male Wistar rats, either control or exposed to crowding stress for 7 days prior to treatment, were used in these experiments. All compounds were injected i.p. Cyclooxygenase COX-1 and COX-2 inhibitors, piroxicam and compound NS-398, IL-1beta and IL-1beta receptor antagonist (IL-1betaRA) were injected 15 min before phenylephrine. Plasma ACTH and serum corticosterone levels were measured 1 h after phenylephrine or IL-1beta injection. Phenylephrine, in respective higher dose administered systemically (0.4 mg/kg i.p.) was almost equally effective as given i.c.v. (30 microg) in stimulating ACTH and corticosterone secretion. Likewise, the extent of the involvement of PG generated by COX-1 and COX-2 in the phenylephrine-induced ACTH and corticosterone secretion was similar after systemic or i.c.v. treatment under both resting and stress conditions. Piroxicam, stronger than compound NS-398, reduced the i.p. phenylephrine-induced ACTH and corticosterone secretion. IL-1beta receptor antagonist (50 microg/kg i.p.) did not significantly affect the inhibitory action of piroxicam on the i.p. phenylephrine-induced ACTH and corticosterone secretion in control rats, but significantly enhanced the inhibition evoked by piroxicam in stressed rats. IL-1beta (2.5 microg/kg i.p.) significantly increased ACTH and corticosterone secretion under basal conditions. Crowding stress for 7 days markedly impaired the IL-1beta-induced ACTH and corticosterone secretion. The mechanism of the stimulatory action of i.p. IL-1beta, which does not cross the blood-brain barrier, may comprise both central and peripheral components of the HPA axis. These results suggest that under basal conditions IL-1beta is not markedly involved in the alpha(1)-adrenergic agonist-induced stimulation of the HPA axis activity. During social crowding stress IL-1beta and prostaglandins are significantly involved in this stimulation.

Nitric oxide in the adrenergic-and CRH-induced activation of hypothalamic-pituitary-adrenal axis.

In this report we investigated the effect of 7-nitroindazole (7-NI), a specific neuronal inhibitor of nitric oxide synthase (nNOS) and L-NAME, a nonselective NOS inhibitor upon the adrenergic- and CRH-induced stimulation of the hypothalamic-pituitary-adrenal axis in nonanesthetized rats. 7-NI given i.p. and L-NAME administered i.c.v. considerably reduced ACTH and corticosterone secretion induced by phenylephrine (30 microg i.c.v.), an alpha(1)-adrenergic receptor agonist. These inhibitors also diminished the HPA response to isoprenaline (20 microg i.c.v.), a nonselective beta-adrenergic receptor agonist, and i.c.v. L-NAME significantly lowered the ACTH and corticosterone response to clenbuterol (10 microg i.c.v.), a selective beta(2)-adrenergic agonist. L-NAME abolished the noradrenaline (NA), an alpha- and beta-receptor agonist-evoked ACTH and corticosterone response, which was reversed by pretreatment with i.p. L-arginine, an endogenous NO substrate. 7-NI abolished the stimulatory action of corticotropin-releasing hormone (CRH 1 microg/kg i.p.) on ACTH but not corticosterone secretion. L-NAME only moderately diminished the CRH-induced ACTH secretion, suggesting that a major part of the CRH-induced HPA axis activation is of neuronal origin. Dihydropyridine, nifedipine, a specific L-type Ca(2+) channel blocker, inhibited significantly the CRH-induced ACTH and corticosterone response in rats exposed to 3 days crowding stress but not in rats under basal conditions. This finding indicates the strategic importance of Ca(2+) influx into the pituitary corticotrops to meet increased secretory requirement under stressful conditions. Collectively, our results point to complex functional relationship between NO, adrenergic agents CRH and Ca(2+) in the regulation of HPA axis activity.

Nitric oxide and prostaglandins in the clenbuterol-induced ACTH and corticosterone secretion.

The present study was designed to determine the involvement of nitric oxide (NO) and prostaglandins (PG) in the stimulatory action of clenbuterol, a selective beta(2)-adrenergic receptor agonist on hypothalamic-pituitary-adrenal (HPA) axis under basal and social crowding stress conditions. Clenbuterol given i.c.v. (10 microg) or i.p. (0.2 mg/kg) considerably increased ACTH and corticosterone secretion. A selective beta(2)-receptor antagonist compound ICI 118551 and non-selective beta-receptor antagonist propranolol given by either route reduced the stimulatory action of clenbuterol. Crowding stress (21 rats in a cage for 7) for 3-7 days significantly reduced the i.c.v. clenbuterol-induced ACTH and corticosterone secretion and i.p. clenbuterol-elicited ACTH secretion. L-NAME, mainly endothelial nitric oxide synthase (NOS) blocker, stronger than L-NNA, a neuronal NOS blocker, reduced the clenbuterol-evoked ACTH and corticosterone secretion in control rats but did not significantly alter this secretion already reduced by crowding stress. Piroxicam, predominantly constitutive cyclooxygenase (COX-1) inhibitor, given i.p. significantly diminished the i.p. clenbuterol-induced ACTH and corticosterone secretion in control rats and tended to reverse the reduction of ACTH secretion by crowding stress. These results indicate that clenbuterol, a selective beta(2)-adrenoceptor agonist, is much stronger stimulator of the HPA axis than isoprenaline, a non-selective beta-receptor agonist. Social crowding stress reduces to a larger extent the HPA response to beta(2)-receptor stimulation. Likewise, in the HPA axis stimulation via beta(2)-adrenoceptors endogenous NO and prostaglandins are significantly involved. Beta2-adrenoceptor is a dominant functional subtype of beta-receptor in the stimulatory and modulatory signals regulating the HPA axis activity under basal and social stress conditions.

Effect of subdiaphragmatic vagotomy and cholinergic agents in the hypothalamic-pituitary-adrenal axis activity.

In the present study, we examined whether the vagus nerve is involved in mediating the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by cholinergic muscarinic and nicotinic agonists, carbachol and nicotine. The site of HPA axis muscarinic stimulation was determined using peripheral (i.p.) and intracerebroventricular (i.c.v.) administration of carbachol, atropine sulphate (AtrS) and atropine hydrobromide (AtrBr). The i.p. carbachol-(0.5 mg/kg)-induced corticosterone response was significantly reduced by i.p. pretreatment with AtrBr (0.1 mg/kg), but was not diminished by i.c.v. AtrS (0.1 mug). The increase in corticosterone secretion induced by i.c.v. carbachol (2 microg) was totally abolished by i.c.v. pretreatment with AtrS (0.1 microg) but was not altered by i.p. AtrBr. Subdiaphragmatic vagotomy performed 2 weeks earlier substantially decreased the i.p. carbachol (0.2 mg/kg)-induced ACTH response and markedly augmented ACTH and corticosterone response to a higher dose of carbachol (0.5 mg/kg) in comparison with the responses in sham operated rats. Vagotomy abolished the stimulatory effect of i.p. nicotine in a low dose (1 mg/kg) on ACTH and corticosterone secretion; the ACTH response to higher dose (2.5 mg/kg) was considerably reduced, while corticosterone response remained unaffected. These results suggest that carbachol given i.c.v. evokes considerable corticosterone response by stimulation of central cholinergic muscarinic receptors. A major part of the i.p. carbachol-induced corticosterone secretion results from peripheral cholinergic muscarinic receptor stimulation. Subdiaphragmatic vagotomy moderately intensified the carbachol-induced ACTH and corticosterone secretion. Vagotomy significantly reduced the nicotine-induced ACTH secretion, possibly by the involvement of vagal afferents. The nicotine-induced corticosterone secretion is not exclusively regulated by circulating ACTH but by various intra-adrenal regulatory components.

The involvement of nitric oxide and prostaglandins in the cholinergic stimulation of hypothalamie-pituitary-adrenal response during crowding stress.

The aim of the present study was to determine the effect of social crowding stress and significance of nitric oxide (NO) and prostaglandins (PG) generated by constitutive and inducible nitric oxide synthase (NOS) and cyclooxygenase (COX) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by cholinergic muscarinic receptor agonist carbachol. Inhibitors of neuronal NOS (nNOS) L-NNA, general NOS L-NAME and inducible NOS (iNOS) aminoguanidine, as well as inhibitors of COX-1, piroxicam, and COX-2, compound NS-398 were administered 15 min prior to carbachol to control or crowded rats (24 rats in cage for 7, during 3 and 7 days). In stressed rats L-NAME, L-NNA and aminoguanidine significantly intensified the carbachol-induced ACTH and corticosterone secretion, like in control rats. Piroxicam, markedly decreased the carbachol-induced ACTH and corticosterone response under either basal or stress conditions. Compound NS-398 did not markedly alter the carbachol-induced HPA response in control and stressed rats. Crowding stress (3 days) significantly impaired the i.c.v. prostaglandin E(2)-induced ACTH response. Corticotropin releasing hormone (CRH) receptor antagonists, alpha-helical CRH [9-14], given i.c.v. did not alter the PGE(2)-evoked corticosterone response in either control or stressed rats, indicating that hypothalamic CRH is not involved in the PGE(2)-induced central stimulation of HPA axis. In control rats L-NAME considerably enhanced, while L-arginine, a physiological NOS substrate, abolished the PGE(2)-induced ACTH and corticosterone response. In stressed rats this NOS blocker significantly increased and L-Arg reduced the stimulatory effect of PGE(2) on ACTH and corticosterone secretion. The carbachol-induced corticosterone response was significantly increased by pretreatment with nNOS inhibitor L-NNA and was considerably reduced by indomethacin, a general COX inhibitor. Pretreatment with both antagonists left the carbachol-induced corticosterone level unchanged, suggesting an independent and reciprocal effect of NO and PG in the cholinergic stimulation of pituitary-adrenocortical response. These results indicate that in the stimulatory action of muscarinic agonist, carbachol, NO is an inhibitory transmitter under basal and crowding stress conditions. This psychosocial stress does not functionally affect the NOS/NO systems. Prostaglandins are involved in the cholinergic muscarinic-induced stimulation of HPA response to a significant extent in non-stressed rats. PGE(2) may be involved in the carbachol-elicited HPA response under basal and stress conditions. Prostaglandins released in response to muscarinic stimulation did not evoke the hypothalamic CRH mediation. NO significantly impairs and PG stimulates the carbachol-induced HPA response in rats under basal and social stress conditions.

Nitric oxide mediates the interleukin-1beta- and nicotine-induced hypothalamic-pituitary-adrenocortical response during social stress.

We investigated the role of nitric oxide (NO) in the interleukin 1beta (IL-1beta) and nicotine induced hypothalamic-pituitary-adrenal axis (HPA) responses, and a possible significance of CRH and vasopressin in these responses under basal and social stress conditions. Male Wistar rats were crowded in cages for 7 days prior to treatment. All compounds were injected i.p., nitric oxide synthase (NOS) inhibitors, alpha-helical CRH antagonist and vasopressin receptor antagonist 15 min before IL-1beta or nicotine. Identical treatment received control non-stressed rats. Plasma ACTH and serum corticosterone levels were measured 1 h after IL-1beta or nicotine injection. L-NAME (2 mg/kg), a general nitric oxide synthase (NOS) inhibitor, considerably reduced the ACTH and corticosterone response to IL-1beta (0.5 microg/rat) the same extent in control and crowded rats. CRH antagonist almost abolished the nicotine-induced hormone responses and vasopressin antagonist reduced ACTH secretion. Constitutive endothelial eNOS and neuronal nNOS inhibitors substantially enhanced the nicotine-elicited ACTH and corticosterone response and inducible iNOS inhibitor, aminoguanidine, did not affect these responses in non-stressed rats. Social stress significantly attenuated the nicotine-induced ACTH and corticosterone response. In crowded rats L-NAME significantly deepened the stress-induced decrease in the nicotine-evoked ACTH and corticosterone response. In stressed rats neuronal NOS antagonist did not alter the nicotine-evoked hormone responses and inducible NOS inhibitor partly reversed the stress-induced decrease in ACTH response to nicotine. These results indicate that NO plays crucial role in the IL-1beta-induced HPA axis stimulation under basal and social stress conditions. CRH and vasopressin of the hypothalamic paraventricular nucleus may be involved in the nicotine induced alterations of HPA axis activity. NO generated by eNOS, but not nNOS, is involved in the stress-induced alterations of HPA axis activity by nicotine.

Psychosocial stress affects the involvement of prostaglandins and nitric oxide in the lipopolysaccharide-induced hypothalamic-pituitary-adrenal response.

The role of prostaglandins and nitric oxide (NO), generated after peripheral lipopolysaccharide (LPS) administration, in the adaptation of hypothalamic-pituitary-adrenal (HPA) axis under stressful circumstances remains to be elucidated. The aim of the present study was to assess the effect of chronic repetitive restraint or social crowding stress on the involvement of nitric oxide and prostaglandins in the LPS-induced pituitary-adrenocortical response. Male Wistar rats were restrained in metal tubes 2 x 10 min/day or crowded in cages for 7 days prior to treatment. All compounds were injected i.p., cyclooxygenase (COX) and nitric oxide synthase (NOS) inhibitors 15 min before LPS. Two hrs after injection LPS induced a significant increase in ACTH and corticosterone secretion. Repeated restraint impaired more potently than crowding stress the LPS-induced HPA-response. Indomethacin, a non-selective COX inhibitor, considerably reduced the LPS-induced HPA response in non-stressed rats and to a lesser extent diminished this response in repeatedly restrained or crowded rats. Neuronal NOS inhibitor, Nomega-nitro-L-arginine decreased the LPS-induced HPA response, more potently in control than crowded rats. Aminoguanidine, an iNOS inhibitor, diminished the LPS-elicited ACTH response in crowded rats. These results indicate that prostaglandins and NO generated by neuronal and inducible NOS are involved in the LPS-induced HPA axis response under basal conditions and during its adaptation to chronic social stress circumstances.

Nitric oxide and prostaglandin systems in the stimulation of hypothalamic-pituitary-adrenal axis by neurotransmitters and neurohormones.

The review presents our results on the regulatory role of prostaglandins (PG) and nitric oxide (NO) in the activation of hypothalamic-pituitary-adrenal (HPA) axis by cholinergic, adrenergic and histaminergic systems and by neurohormones: corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) under basal conditions. The synthesis of endogenous PG or NO was inhibited by non-selective and selective cyclooxygenase (COX) antagonists and nitric oxide synthase (NOS) blockers given 15 min before the respective receptor agonist and HPA axis activity was assessed 1 h later by measuring plasma ACTH and serum corticosterone levels. The muscarinic agent - carbachol-induced HPA response was considerably supressed by piroxicam, a predominantly constitutive cyclooxygenase (COX-1) inhibitor and significantly diminished by indomethacin, a non-selective COX blocker, but was unaffected by compound NS-398, an inducible cyclooxygenase (COX-2) antagonist. A non-selective NOS antagonist L-NAME and neuronal NOS blocker L-NNA significantly intensified the carbachol-induced corticosterone secretion. The nicotine-induced increase in ACTH and corticosterone response was significantly supressed by piroxicam, and diminished by indomethacin, but was significantly augmented by L-NAME and L-NNA. The inhibition of PG synthesis by indomethacin totally abolished or reversed the increase of nicotine-induced hormone responses to both NOS blockers. The i.c.v. phenylephrine, an alpha(1)-adrenergic receptor agonist - evoked HPA response was significantly impaired by piroxicam and compound NS-398 and more potently reduced by L-NAME. The i.c.v. clonidine, an alpha(2)-adrenergic agonist - elicited HPA response was also considerably decreased by piroxicam, compound NS-398 and L-NAME. By contrast, the stimulatory effect of i.c.v. isoprenaline, a non-selective beta-adrenergic agonist, was not altered by either COX or NOS inhibitors. The i.c.v. histamine- and HTMT, a histamine H(1)-agonist-induced ACTH and corticosterone response were significantly diminished by piroxicam and indomethacin, respectively. Compound NS-398, did not markedly alter the HPA response to HTMT or amthamine, a histamine H(2) receptor agonist. Inhibition of endogenous NO synthesis by a neuronal NOS inhibitor 7-nitroindazole markedly enhanced the histamine-induced hormone secretion, abolished the HTMT-induced response and did not substantially alter the amthamine-evoked ACTH and corticosterone secretion. COX blockers did not significantly affect the CRH-induced HPA response and the inhibition of NO synthesis by L-NNA markedly intensified ACTH response. The vasopressin-stimulated increase in HPA response, was considerably reduced by the inhibition of PG synthesis by both COX antagonists while inhibition of NO synthesis by NOS blockers greatly enhanced this response. The involvement of PG and NO in the neurohormonal regulation of HPA activity depends mainly on greatly complex and tightly regulated mechanisms at the level of second messengers IP(3) and adenylyl cyclase systems.

Role of prostaglandins and nitric oxide in the lipopolysaccharide-induced ACTH and corticosterone response.

This study was designed to determine the role of endogenous prostaglandins (PG) and nitric oxide (NO) in the lipopolysaccharide (LPS)-induced ACTH and corticosterone secretion in conscious rats. LPS (0.5 and 1 mg/kg) given i.p. stimulated the hypothalamic-pituitary-adrenocortical (HPA) activity measured 2 h later. A non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg i.p.), piroxicam (2 mg/kg i.p.), a more potent antagonist of constitutive cyclooxygenase (COX-1) and compound NS-398 (2 mg/kg i.p.), a selective inhibitor of inducible cyclooxygenase (COX-2) given 30 min before LPS (1 mg/kg i.p.) significantly diminished both the LPS-induced ACTH and corticosterone secretion. COX-2 blocker was the most potent inhibitor of ACTH secretion (72.3%). Nomega-nitro-L-arginine methyl ester (L-NAME 2 and 10 mg/kg i.p.), a non-selective nitric oxide synthase (NOS) blocker given 15 min before LPS did not substantially alter plasma ACTH and corticosterone levels 2 h later. Aminoguanidine (AG 100 mg/kg i.p.), a selective inducible nitric oxide synthase (iNOS) inhibitor, considerably enhanced ACTH and corticosterone secretion induced by a lower dose (0.5 mg/kg) of LPS and did not significantly alter this secretion after a larger dose (1 mg/kg) of LPS. L-NAME did not markedly affect the indomethacin-induced inhibition of ACTH and corticosterone response. By contrast, aminoguanidine abolished the indomethacin-induced reduction of ACTH and corticosterone secretion after LPS. These results indicate an opposite action of PG generated by cyclooxygenase and NO synthesized by iNOS in the LPS-induced HPA-response.

Role of nitric oxide in the nicotine-induced pituitary-adrenocortical response.

Nitric oxide (NO) is a major signaling molecule and biological mediator of the hypothalamic-pituitary-adrenal (HPA) axis. We investigated the role of NO formed by endothelial (e), neuronal (n) and inducible (i) nitric oxide synthase (NOS) in the stimulatory effect of nicotine on the HPA axis in rats under basal conditions. Also possible interaction of NOS systems with endogenous prostaglandins (PG) in that stimulation was assessed. NOS and cyclooxygenase inhibitors were administered i.p. 15 min prior to nicotine (2, 5 mg/kg i.p.). Plasma ACTH and serum corticosterone levels were measured 1 h after nicotine injection. NOS blockers given alone did not markedly affect the resting ACTH and corticosterone levels. L-NAME (2-10 mg/kg), a broad spectrum NOS inhibitor considerably and dose dependently enhanced the nicotine-induced ACTH and corticosterone secretion. L-NNA (2 mg/kg) and 7-nitroindazole (7-NI 20 mg/kg), neuronal NOS inhibitors in vivo also significantly augmented the nicotine-induced ACTH and corticosterone levels. L-arginine greatly impaired the nicotine-induced hormone responses and reversed the L-NNA elicited enhancement of the nicotine-evoked ACTH and corticosterone response. In contrast to the constitutive eNOS and nNOS antagonists, an inducible NOS antagonist guanethidine (50-100 mg/kg i.p.) did not substantially affect the nicotine-elicited pituitary-adrenocortical responses. Indomethacin (2 mg/kg i.p.), a non-selective cyclooxygenase blocker abolished the L-NAME and L-NNA-induced enhancement of the nicotine-evoked ACTH and corticosterone response. These results indicate that NO is an inhibitory mediator in the HPA axis activity. Inhibition of its generation by eNOS and nNOS significantly enhances the nicotine-induced HPA response. Under basal conditions iNOS is not involved in the nicotine-induced ACTH and corticosterone secretion. Prostaglandins play an obligatory role in the response of HPA axis to systemic nicotine administration.

Repeated handling, restraint, or chronic crowding impair the hypothalamic-pituitary-adrenocortical response to acute restraint stress.

The purpose of the present study was to assess whether, and to what extent prior handling, restraint or social crowding stress during 3-10 days affects the hypothalamic-pituitary-adrenocortical (HPA) response to an acute short-lasting restraint stress. Also the effect of a feedback inhibitory mechanism of corticosterone in the impairment of HPA axis by these stressors was investigated. Male Wistar rats were pretreated with handling 1 min/day for 3-10 days, restraint 2 times daily for 3-7 days and crowding stress for 7 days before exposure to acute restraint stress in metal tubes for 10 min. Some group of rats received exogenous s.c. corticosterone either once 25 mg/kg or 2 times daily 10 mg/kg for 3-10 days before restraint stress. After the last restraint the rats were decapitated and their trunk blood was collected for the measurement of plasma ACTH and serum corticosterone levels. Handling for 3-7 days, restraint for 3-7 days, and crowding for 7 days and a single pretreatment with corticosterone--all significantly and to a similar extent inhibited the restraint stress-induced increase in ACTH and corticosterone secretion. Chronic pretreatment with corticosterone blunted the restraint stress-induced increase in HPA axis activity. These results indicate that repeated short-lasting stress induced by handling, restraint, or crowding potently attenuates the acute restraint stress-induced stimulatory action of the HPA axis. They also indicate adaptive action of moderate stress on the HPA axis response to acute stress. The results also suggest that a short-lasting hypersecretion of corticosterone during psychological stress may induce a prolonged feedback inhibition of the HPA axis activity. The attenuation of HPA axis response by prior handling has also obvious methodological implications.

Effect of cyclooxygenase inhibitors on the vasopressin induced ACTH and corticosterone response during crowding stress.

The aim of the present study was to compare the effect of social stress on the corticotropin releasing hormone (CRH) and arginine vasopressin (AVP)-induced pituitary-adrenocortical activity. Also the significance of prostaglandins (PG) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by AVP under basal and crowding stress conditions was investigated. The control rats were housed 7 in a standard cage and stressed rats were crowded 24 in a cage of the same size during 7 days. The activity of HPA axis was determined by measuring plasma ACTH and serum corticosterone levels 1 h after i.p. AVP administration. Indomethacin (2.0 mg/kg i.p.), a non-selective COX inhibitor, piroxicam (0.2, 2.0, and 5.0 mg/kg), a more potent COX-1 than COX-2 inhibitor, and compound NS-398 (0.2 and 2.0 mg/kg) a selective COX-2 inhibitor, were administered i.p. 15 min prior to AVP (5.0 microg/kg i.p.) to control or crowded rats. The obtained results indicate that social stress for 7 days considerably inhibits the stimulatory action of AVP on ACTH secretion, while it intensifies the CRH-induced ACTH secretion. Indomethacin, piroxicam and NS-398 significantly diminished the AVP-elicited ACTH and corticosterone secretion in non-stressed rats. None of these COX antagonist induced any significant inhibition of the AVP-induced ACTH and corticosterone secretion in stressed rats. Therefore, PG generated by COX-1 or COX-2 do not participate to a significant extent in the HPA stimulation by AVP during crowding stress. These results suggest that social crowding stress desensitizes the PG stimulatory mechanism which considerably mediates the AVP-induced HPA stimulation under basal conditions. The results contrast with a lack of any involvement of PG in the CRH-induced stimulation of HPA response under basal or crowding stress conditions.

Effect of cyclooxygenase inhibitors on the CRH-induced pituitary-adrenocortical activity during crowding stress.

The aim of the present study was to determine the effect of social stress and significance of prostaglandins (PG) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by corticotropin releasing hormone (CRH) under basal and social crowding stress conditions. The stressed rats were crowded in groups of 24 to a cage for 3 or 7 days, whereas the control animals were haused in groups of 7 to a cage of the same size. The activity of HPA axis was determined by measuring plasma ACTH and serum corticosterone levels 1 h after i.p. CRH administration. Inhibitors of COX-1, piroxicam (0.2, 2.0, and 5.0 mg/kg), and COX-2, compound NS-398 (0.2 and 2.0 mg/kg), were administered i.p. 15 min prior to CRH (0.1 microg/kg i.p.) to control or crowded rats. The obtained results indicate that social stress for 3 and 7 days markedly intensifies the stimulatory action of CRH on ACTH secretion. Neither piroxicam nor NS-398 induce any significant effect on the CRH-elicited ACTH and corticosterone secretion in non-stressed or crowded rats. Therefore, PG generated by COX-1 or COX-2 do not participate to a significant extent in the stimulation of HPA axis by CRH under either basal conditions or during crowding stress. These results also indicate that the stimulatory action of CRH on ACTH secretion is not only completely resistant to desensitization but is sensitized during social crowding stress. The results contrast with a significant involvement of PG in the vasopressin-induced stimulation of HPA response during crowding stress.

Influence of cyclooxygenase inhibitors on the central histaminergic stimulations of hypothalamic - pituitary - adrenal axis.

Brain histamine participates in central regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Endogenous prostaglandins modulate signal transduction of different neurotransmitters involved in activation of HPA axis. In the present experiment we investigated whether endogenous prostaglandins are involved in the stimulation of ACTH and corticosterone secretion by histaminergic systems in the rat brain. Histamine (50 microg), histamine-trifluoromethyl-toluidine derivative (HTMT, 75microg) a selective and potent H(1)-receptor agonist, and amthamine (50 microg) a H(2)-receptor agonist given intracerebroventricularly (i.c.v.) to non-anesthetized rats considerably increased ACTH and corticosterone secretion 1h after administration. A non-selective cyclooxygenase inhibitor indomethacin (2 mg/kg i.p. or 10 microg i.c.v.), piroxicam (0.02 and 0.2 microg i.c.v.) a more potent antagonist of constitutive cyclooxygenase (COX-1) and compound NS-398 (0.1 and 1.0 microg i.c.v.), a selective inhibitor of inducible cyclooxygenase (COX-2) were given 15 min before histamine and histamine receptor agonists. One hour after the last injection trunk blood from decapitated rats was collected for hormones determination. The histamine-induced ACTH and corticosterone secretion was significantly diminished by piroxicam and was not markedly altered by indomethacin and compound NS-398. The HTMT-elicited increase in ACTH and corticosterone secretion was significantly prevented by indomethacin and was not affected by piroxicam or compound NS-398. The amthamine-evoked increase in ACTH and corticosterone secretion was not markedly influenced by any cyclooxygenase blocker applied in the present experiment. These results indicate that the histamine H(1)-receptor transmitted central stimulation of the HPA axis is considerably mediated by prostaglandins generated by consititutive cyclooxygenase, whereas stimulation transmitted via H(2)-receptor does not significantly depend on endogenous prostaglandins mediation.

Effect of constitutive- and inducible-cyclooxygenase in the carbachol-induced pituitary-adrenocortical response during social stress.

Acetylcholine potently stimulates the hypothalamic-pituitary-adrenal (HPA) axis. Cholinergic receptor agonist carbachol, given intraperitoneally (i.p.) or into the lateral cerebral ventricle (i.c.v.) to non-anesthetized rats acts via multiple pathways to stimulate the HPA axis. The present study sought to determine 1) the functional selectivity of carbachol for cholinergic muscarinic and/or nicotinic receptors involved in the stimulation of HPA axis; 2) the involvement of prostaglandins (PGs) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the carbachol-induced ACTH and corticosterone secretion in non-stressed rats and animals exposed to social crowding stress for 7 days (24 per a cage for 6). Carbachol was given i.c.v. or i.p. and cholinergic receptor antagonists or cyclooxygenase isoenzyme antagonists were given by the same routes 15 min earlier. One hour after the last injection trunk blood was taken for ACTH and corticosterone determinations. Atropine (0.1 microg i.c.v.), a cholinergic receptor antagonist, totally abolished the carbachol (2 microg i.c.v.)-induced ACTH and corticosterone secretion and mecamylamine (20 microg i.c.v.), a selective nicotinic receptor antagonist, did not affect this secretion. This finding indicates that carbachol functions as a selective central cholinergic muscarinic receptor agonist for the HPA axis stimulation. Crowding stress significantly diminished the carbachol (0.2 mg/kg i.p.)-induced plasma ACTH and corticosterone levels measured 1 hr after administration. Pretreatment with indomethacin (2 mg/kg i.p.), a non-selective cyclooxygenase inhibitor, significantly diminished the ACTH and corticosterone responses to carbachol (0.2 mg/kg i.p.) in control rats and moderately decreased these responses in stressed rats. Piroxicam (0.2 and 2.0 mg/kg i.p.), a COX-1 inhibitor, considerably impaired the carbachol-induced ACTH and corticosterone responses in control rats and markedly diminished these responses in stressed rats. A selective COX-2 blocker, compound NS-398 (0.2 and 2.0 mg/kg i.p.), substantially decreased the carbachol-induced hormones secretion in control rats but did not markedly alter this secretion in stressed rats. These results indicate that in the carbachol-induced HPA axis activation PGs generated by COX-1 are considerably and to a much greater extent involved than PGs generated by COX-2. Social stress markedly diminishes the mediation of PGs generated by COX-1 but PGs synthesized by COX-2 do not substantially participate in the carbachol-induced HPA response.

Effect of adrenergic antagonists and cyclooxygenase inhibitors on the nicotine-induced hypothalamic-pituitary-adrenocortical activity.

Nicotine is a potent stimulus for the hypothalamic-pituitary-adrenal (HPA) axis. Systemic nicotine acts via central mechanisms to stimulate by multiple pathways the release of ACTH from the anterior pituitary corticotrops and corticosterone from the adrenal cortex. Nicotine may stimulate indirectly the hypothalamic paraventricular nucleus, the site of the corticotropin-releasing hormone (CRH) neurons which activates ACTH release. In the present studies an involvement of adrenergic system and prostaglandins synthesized by constitutive cyclooxygenase (COX-1) and inducible cyclooxygenase (COX-2) in the nicotine-induced HPA response in rats was investigated. Nicotine (2.5-5 mg/kg i.p.) significantly increased plasma ACTH and corticosterone levels measured 1 hr after administration. Adrenergic receptor antagonists or COX inhibitors were injected i.p. 15 min prior to nicotine and the rats were decapitated 1 hr after the last injection. Prazosin (0.01-0.1 mg/kg), an alpha1-adrenergic antagonist, significantly decreased the nicotine-evoked ACTH and corticosterone secretion. Yohimbine (0.1-1.0 mg/kg), an alpha2-adrenergic antagonist, moderately diminished ACTH response, and propranolol (0.1-10 mg/kg), a beta-adrenergic antagonist, did not significantly alter the nicotine-induced hormones secretion. Pretreatment with piroxicam (0.2-2.0 mg/kg), a COX-1 inhibitor, considerably impaired the nicotine-induced ACTH and corticosterone secretion. Compound NS-398 (0.2-5.0 mg/kg), a selective COX-2 blocker did not markedly alter these hormones secretion, and indomethacin (2 mg/kg), a non-selective COX inhibitor significantly diminished ACTH response. These results indicate that systemic nicotine stimulates the HPA axis indirectly, and both adrenergic system and prostaglandins are significantly involved in this stimulation. Noradrenaline, stimulating postsynaptic alpha1-adrenergic receptors, and prostaglandins, synthesized by COX-1 isoenzyme, are of crucial significance in the nicotine-induced ACTH and corticosterone secretion.

Involvement of prostaglandins in the nicotine-induced pituitary-adrenocortical response during social stress.

The present study examined the functional selectivity of nicotine for nicotinic acetylcholine receptors in the stimulation of the hypothalamic-pituitary-adrenal (HPA) axis, the effect of social crowding stress on HPA response to nicotine and the involvement of prostaglandins synthesized by constitutive cyclooxygenase (COX-1) and inducible cyclooxygenase (COX-2) in the nicotine-induced HPA response in rats crowded (24 per a box instead 7) for 7 days. Nicotine (2.5-5.0 mg/kg i.p.) significantly increased plasma ACTH and corticosterone levels measured 1 h after administration. Mecamylamine (50 mg i.c.v.), a selective nicotinic receptor antagonist, atropine (0.1 mg/kg i.p.) a non-selective cholinergic receptor antagonist, or COX inhibitors were injected 15 min prior to nicotine and the rats were decapitated 1 h after the last injection. Mecamylamine abolished the nicotine-induced ACTH response and significantly diminished corticosterone response. Atropine did not alter ACTH response and modestly diminished corticosterone response to nicotine. Crowding stress significantly impaired the nicotine-evoked ACTH and corticosterone secretion. Pretreatment with piroxicam (0.2-2.0 mg/kg), a COX-1 inhibitor, considerably diminished the nicotine-induced ACTH and corticosterone secretion in control and crowded rats. Compound NS-398 (0.2-5.0 mg/kg), a selective COX-2 blocker, did not markedly alter the nicotine-induced hormones secretion in either control or stressed rats. Indomethacin (2 mg/kg), a non-selective COX inhibitor diminished significantly, but to a lesser extent than piroxicam, the nicotine-stimulated ACTH and corticosterone response. These results indicate that systemic nicotine stimulates the HPA axis selectively via nicotinic acetylcholine receptors. Chronic social stress significantly impairs the nicotine stimulated ACTH and corticosterone secretion. Prostaglandins, generated by COX-1- but not by COX-2- isoenzyme, are of crucial significance in the nicotine-induced ACTH and corticosterone secretion in both control and stressed rats.

A single corticosterone pretreatment inhibits the hypothalamic-pituitary-adrenal responses to adrenergic and cholinergic stimulation.

The purpose of the present study was to determine whether an increased plasma corticosterone or dexamethasone levels induced by a single corticosterone or dexamethasone injection to conscious rats affects the hypothalamic-pituitary-adrenocortical (HPA) activity induced by adrenergic and cholinergic agonists. Male Wistar rats were pretreated subcutaneously (s.c.) with a single dose of dexamethasone (5 mg/kg) or corticosterone (25 mg/kg) 24 or 48 h before intraperitoneal (i.p.) administration of adrenergic agonists: phenylephrine, an alpha1-adrenergic receptor agonist, clenbuterol, a beta2-adrenergic agonist and noradrenaline acting predominantly on alpha1-adrenoreceptors, and cholinergic agonists: carbachol, a predominant muscarinic receptor agonist and nicotine, a nicotinic receptor agonist. Dexamethasone profoundly decreased the resting ACTH levels in control rats and given 24 h before each of the stimulatory agonist abolished the adrenergic- and cholinergic agonists-induced ACTH and corticosterone responses. Pretreatment with corticosterone of control rats did not substantially alter the resting plasma ACTH and serum corticosterone levels measured 24 and 48 h later. A single pretreatment with corticosterone abolished or powerfully inhibited, perhaps by a feedback mechanism, the ACTH and corticosterone responses induced 24 and 48 h later by all adrenergic and cholinergic agonists used in this study. These results indicate that prolonged administration of corticosterone is not necessary to induce almost complete suppression of the HPA responsiveness to adrenergic or cholinergic stimulation. Chronic treatment with corticosteroids to achieve glucocorticoid receptors desensitization does not seem to be required.

Effect of social stress on COX-1 and COX-2-induced alterations in the adrenergic agonists-evoked hypothalamic-pituitary-adrenal responses.

The purpose of the present study was to investigate the contribution of prostaglandins (PGs) synthesized by constitutive (COX-1) and inducible (COX-2) cyclooxygenase to stimulation of the hypothalamic-pituitary-adrenal (HPA) axis by adrenergic receptor agonists in rats under social crowing stress 3 days, (21 per a cage for 6) animals. The effects of phenylephrine, clonidine and isoprenaline, an alpha1-, alpha2- and beta-adrenergic agonist, respectively, in the presence and absence of COX-1 inhibitor, piroxicam, and COX-2 inhibitor, compound NS-398, on ACTH and corticosterone secretion in stressed rats were compared with these effects in non-stressed animals. All drugs were given intracerebroventricularly (i.c.v.), COX inhibitors 15 min before adrenergic agonists. Piroxicam (0.02 microg) and NS-398 (0.1 microg) significantly reduced the phenylephrine (30 microg) -induced ACTH and corticosterone secretion in both stressed and non-stressed rats. Piroxicam (0.02 microg) and NS-398 (0.01 microg) moderately decreased the clonidine (10 microg) -evoked hormone responses in control rats but did not alter these responses in stressed rats. Piroxicam (0.2 microg) and NS-398 (0.1 microg) moderately diminished the isoprenaline (20 microg) -evoked ACTH and corticosterone response in control rats, while in stressed rats these inhibitors did not significantly alter the isoprenaline-induced rise in ACTH and corticosterone secretion. These results indicate that in hypothalamic structures involved in the regulation of adrenergic agonists-induced HPA stimulation COX-2 is expressed under physiological synaptic activity. Social crowding stress does not alter the significant involvement of prostaglandins in the HPA response induced by stimulation of central alpha1-adrenergic receptors. Prostaglandins are of lesser importance in activation of the HPA axis by alpha2- and beta-adrenergic receptors under basal and social stress conditions.