Partial Agonist Activity of Neonicotinoids on Rat Nicotinic Receptors: Consequences over Epinephrine Secretion and In Vivo Blood Pressure.

Neonicotinoid insecticides are nicotine-derived molecules which exert acute neurotoxic effects over the insect central nervous system by activating nicotinic acetylcholine receptors (nAChRs). However, these receptors are also present in the mammalian central and peripheral nervous system, where the effects of neonicotinoids are faintly known. In mammals, cholinergic synapses are crucial for the control of vascular tone, blood pressure and skeletal muscle contraction. We therefore hypothesized that neonicotinoids could affect cholinergic networks in mammals and sought to highlight functional consequences of acute intoxication in rats with sub-lethal concentrations of the highly used acetamiprid (ACE) and clothianidin (CLO). In this view, we characterized their electrophysiological effects on rat α3ß4 nAChRs, knowing that it is predominantly expressed in ganglia of the vegetative nervous system and the adrenal medulla, which initiates catecholamine secretion. Both molecules exhibited a weak agonist effect on α3ß4 receptors. Accordingly, their influence on epinephrine secretion from rat adrenal glands was also weak at 100 µM, but it was stronger at 500 µM. Challenging ACE or CLO together with nicotine (NIC) ended up with paradoxical effects on secretion. In addition, we measured the rat arterial blood pressure (ABP) in vivo by arterial catheterization. As expected, NIC induced a significant increase in ABP. ACE and CLO did not affect the ABP in the same conditions. However, simultaneous exposure of rats to both NIC and ACE/CLO promoted an increase of ABP and induced a biphasic response. Modeling the interaction of ACE or CLO on α3ß4 nAChR is consistent with a binding site located in the agonist pocket of the receptor. We present a transversal experimental approach of mammal intoxication with neonicotinoids at different scales, including in vitro, ex vivo, in vivo and in silico. It paves the way of the acute and chronic toxicity for this class of insecticides on mammalian organisms.

Stimulation of brain α7-nicotinic acetylcholine receptors suppresses the rat micturition through brain GABAergic receptors.

Brain nicotinic acetylcholine receptors (nAChRs) reportedly suppress the micturition, but the mechanisms responsible for this suppression remain unclear. We previously reported that intracerebroventricularly administered (±)-epibatidine (non-selective nAChR agonist) activated the sympatho-adrenomedullary system, which can affect the micturition. Therefore, we investigated (1) whether intracerebroventricularly administered (±)-epibatidine-induced effects on the micturition were dependent on the sympatho-adrenomedullary system, and (2) brain nAChR subtypes involved in the (±)-epibatidine-induced effects in urethane-anesthetized male Wistar rats. Plasma noradrenaline and adrenaline (catecholamines) were measured just before and 5 min after (±)-epibatidine administration. Evaluation of urodynamic parameters, intercontraction intervals (ICI) and maximal voiding pressure (MVP) by cystometry was started 1 h before (±)-epibatidine administration or intracerebroventricular pretreatment with other drugs and continued 1 h after (±)-epibatidine administration. Intracerebroventricularly administered (±)-epibatidine elevated plasma catecholamines and prolonged ICI without affecting MVP, and these changes were suppressed by intracerebroventricularly pretreated mecamylamine (non-selective nAChR antagonist). Acute bilateral adrenalectomy abolished the (±)-epibatidine-induced elevation of plasma catecholamines, but had no effect on the (±)-epibatidine-induced ICI prolongation. The latter was suppressed by intracerebroventricularly pretreated methyllycaconitine (selective α7-nAChR antagonist), SR95531 (GABAA antagonist), and SCH50911 (GABAB antagonist), but not by dihydro-ß-erythroidine (selective α4ß2-nAChR antagonist). Intracerebroventricularly administered PHA568487 (selective α7-nAChR agonist) prolonged ICI without affecting MVP, similar to (±)-epibatidine. These results suggest that stimulation of brain α7-nAChRs suppresses the rat micturition through brain GABAA/GABAB receptors, independently of the sympatho-adrenomedullary outflow modulation.

Vagotomy Affects Lipopolysaccharide-Induced Changes of Urocortin 2 Gene Expression in the Brain and on the Periphery.

The corticotropin-releasing hormone family of peptides is involved in regulating the neuroendocrine stress response. Also, the vagus nerve plays an important role in the transmission of immune system-related signals to brain structures, thereby orchestrating the neuroendocrine stress response. Therefore, we investigated gene expression of urocortin 2 (Ucn2) and c-fos, a markers of neuronal activity, within the hypothalamic paraventricular nucleus (PVN), a brain structure involved in neuroendocrine and neuroimmune responses, as well as in the adrenal medulla and spleen in vagotomized rats exposed to immune challenge. In addition, markers of neuroendocrine stress response activity were investigated in the adrenal medulla, spleen, and plasma. Intraperitoneal administration of lipopolysaccharide (LPS) induced a significant increase of c-fos and Ucn2 gene expression in the PVN, and adrenal medulla as well as increases of plasma corticosterone levels. In addition, LPS administration induced a significant increase in the gene expression of tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) in the adrenal medulla. In the spleen, LPS administration increased gene expression of c-fos, while gene expression of TH and PNMT was significantly reduced, and gene expression of Ucn2 was not affected. Subdiaphragmatic vagotomy significantly attenuated the LPS-induced increases of gene expression of c-fos and Ucn2 in the PVN and Ucn2 in the adrenal medulla. Our data has shown that Ucn2 may be involved in regulation of the HPA axis in response to immune challenge. In addition, our findings indicate that the effect of immune challenge on gene expression of Ucn2 is mediated by vagal pathways.

Mechanisms for pituitary adenylate cyclase-activating polypeptide-induced increase in excitability in guinea-pig and mouse adrenal medullary cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts on adrenal medullary (AM) cells as a neurotransmitter of the sympathetic preganglionic nerve. In guinea-pig AM cells, PACAP induces little catecholamine secretion, but enhances secretion evoked by stimulants, whereas in other animals, such as mouse, PACAP itself induces depolarization and/or catecholamine secretion. The present studies aim to explore the physiological implication of these species differences in PACAP actions, the ion channel mechanism for PACAP-induced depolarization, and the mechanism for facilitation of muscarinic receptor-mediated cation currents in mouse and guinea-pig AM cells. The perforated patch clamp technique was used to record the whole-cell current in isolated AM cells. The amplitudes of 3 nM PACAP-induced inward currents were significantly larger in mouse AM cells than guinea-pig, whereas 1 µM muscarine-induced currents were larger in guinea-pig AM cells than mouse. Exposure to PACAP consistently resulted in enhancement of muscarine-induced currents in guinea-pig AM cells and facilitation of cell membrane insertion of heteromeric TRPC1-TRPC4 channels in response to muscarine in PC12 cells. The PACAP-induced current was inhibited by 30 µM 9-phenanthrol, a specific TRPM4 channel inhibitor, and abolished by replacement of external Na+ with N-methyl D-glucamine. TRPM4-like immunoreactivity was located at the cell periphery in AM cells. The present results indicate that PACAP and muscarinic receptors are major metabotropic receptors mediating generation of depolarizing inward currents in mouse and guinea-pig AM cells, respectively. We conclude that PACAP activates TRPM4-like channels and enhance the muscarinic current through facilitating the membrane insertion of TRPC1-TRPC4 channels in AM cells.

Stimulation of brain nicotinic acetylcholine receptors activates adrenomedullary outflow via brain inducible NO synthase-mediated S-nitrosylation.

BACKGROUND AND PURPOSE: We have demonstrated that i.c.v.-administered (±)-epibatidine, a nicotinic ACh receptor (nAChR) agonist, induced secretion of noradrenaline and adrenaline (catecholamines) from the rat adrenal medulla with dihydro-ß-erythroidin (an α4ß2 nAChR antagonist)-sensitive brain mechanisms. Here, we examined central mechanisms for the (±)-epibatidine-induced responses, focusing on brain NOS and NO-mediated mechanisms, soluble GC (sGC) and protein S-nitrosylation (a posttranslational modification of protein cysteine thiol groups), in urethane-anaesthetized (1.0 g·kg-1 , i.p.) male Wistar rats. EXPERIMENTAL APPROACH: (±)-Epibatidine was i.c.v. treated after i.c.v. pretreatment with each inhibitor described below. Then, plasma catecholamines were measured electrochemically after HPLC. Immunoreactivity of S-nitrosylated cysteine (SNO-Cys) in α4 nAChR subunit (α4)-positive spinally projecting neurones in the rat hypothalamic paraventricular nucleus (PVN, a regulatory centre of adrenomedullary outflow) after i.c.v. (±)-epibatidine administration was also investigated. KEY RESULTS: (±)-Epibatidine-induced elevation of plasma catecholamines was significantly attenuated by L-NAME (non-selective NOS inhibitor), carboxy-PTIO (NO scavenger), BYK191023 [selective inducible NOS (iNOS) inhibitor] and dithiothreitol (thiol-reducing reagent), but not by 3-bromo-7-nitroindazole (selective neuronal NOS inhibitor) or ODQ (sGC inhibitor). (±)-Epibatidine increased the number of spinally projecting PVN neurones with α4- and SNO-Cys-immunoreactivities, and this increment was reduced by BYK191023. CONCLUSIONS AND IMPLICATIONS: Stimulation of brain nAChRs can induce elevation of plasma catecholamines through brain iNOS-derived NO-mediated protein S-nitrosylation in rats. Therefore, brain nAChRs (at least α4ß2 subtype) and NO might be useful targets for alleviation of catecholamines overflow induced by smoking.

Diosgenin-caused changes of the adrenal gland histological parameters in a rat model of the menopause.

Diosgenin, a steroidal sapogenin of natural origin, has demonstrated benefits when it comes to the treatment of malignancies, cardiovascular issues and menopausal symptoms. In this study, we investigated the histological changes of the adrenal gland after diosgenin application in a rat model of the menopause. Middle-aged, acyclic female Wistar rats were divided into control (C; n=6) and diosgenin treated (D; n=6) groups. Diosgenin (100mg/kg b.w./day) was orally administered for four weeks, while C group received the vehicle alone. A histological approach included design-based stereology, histochemistry and immunohistochemistry. The adrenal cortex volume decreased in D females by 15% (p<0.05) while the volume of adrenal medulla increased (p<0.05) by 64%, compared to the same parameters in C group. Volume density of the zona glomerulosa (expressed per absolute adrenal gland volume) in D rats increased (p<0.05) by 22% in comparison with C animals. Diosgenin treatment decreased (p<0.05) the volume density of the zona fasciculata (expressed per volume of adrenal cortex) by 15% when compared to C females. Absolute volume of the zona reticularis in D group decreased (p<0.05) by 38% in comparison with the same parameter in C rats. Also, after diosgenin application, the volume density of the zona reticularis (expressed per volume of adrenal cortex) and the zona reticularis cell volume were decreased by 51% and 20% (p<0.05) respectively, compared to C animals. Our results, reflecting a decrease in many stereological parameters of the adrenal cortex, indicate that diosgenin took over the role of corticosteroid precursors and became incorporated into steroidogenesis.

Interleukin-6-mediated signaling in adrenal medullary chromaffin cells.

The pro-inflammatory cytokines, tumor necrosis factor-α, and interleukin-1ß/α modulate catecholamine secretion, and long-term gene regulation, in chromaffin cells of the adrenal medulla. Since interleukin-6 (IL6) also plays a key integrative role during inflammation, we have examined its ability to affect both tyrosine hydroxylase activity and adrenomedullary gene transcription in cultured bovine chromaffin cells. IL6 caused acute tyrosine/threonine phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), and serine/tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3). Consistent with ERK1/2 activation, IL6 rapidly increased tyrosine hydroxylase phosphorylation (serine-31) and activity, as well as up-regulated genes, encoding secreted proteins including galanin, vasoactive intestinal peptide, gastrin-releasing peptide, and parathyroid hormone-like hormone. The effects of IL6 on the entire bovine chromaffin cell transcriptome were compared to those generated by G-protein-coupled receptor (GPCR) agonists (histamine and pituitary adenylate cyclase-activating polypeptide) and the cytokine receptor agonists (interferon-α and tumor necrosis factor-α). Of 90 genes up-regulated by IL6, only 16 are known targets of IL6 in the immune system. Those remaining likely represent a combination of novel IL6/STAT3 targets, ERK1/2 targets and, potentially, IL6-dependent genes activated by IL6-induced transcription factors, such as hypoxia-inducible factor 1α. Notably, genes induced by IL6 include both neuroendocrine-specific genes activated by GPCR agonists, and transcripts also activated by the cytokines. These results suggest an integrative role for IL6 in the fine-tuning of the chromaffin cell response to a wide range of physiological and paraphysiological stressors, particularly when immune and endocrine stimuli converge.

High potassium promotes mutual interaction between (pro)renin receptor and the local renin-angiotensin-aldosterone system in rat inner medullary collecting duct cells.

(Pro)renin receptor (PRR) is predominantly expressed in the collecting duct (CD) with unclear functional implication. It is not known whether CD PRR is regulated by high potassium (HK). Here, we aimed to investigate the effect of HK on PRR expression and its role in regulation of aldosterone synthesis and release in the CD. In primary rat inner medullary CD cells, HK augmented PRR expression and soluble PPR (sPRR) release in a time- and dose-dependent manner, which was attenuated by PRR small interfering RNA (siRNA), eplerenone, and losartan. HK upregulated aldosterone release in parallel with an increase of CYP11B2 (cytochrome P-450, family 11, subfamily B, polypeptide 2) protein expression and upregulation of medium renin activity, both of which were attenuated by a PRR antagonist PRO20, PRR siRNA, eplerenone, and losartan. Similarly, prorenin upregulated aldosterone release and CYP11B2 expression, both of which were attenuated by PRR siRNA. Interestingly, a recombinant sPRR (sPRR-His) also stimulated aldosterone release and CYP11B2 expression. Taken together, we conclude that HK enhances a local renin-angiotensin-aldosterone system (RAAS), leading to increased PRR expression, which in turn amplifies the response of the RAAS, ultimately contributing to heightened aldosterone release.

Catecholamine secretion by chemical hypoxia in guinea-pig, but not rat, adrenal medullary cells: differences in mitochondria.

The effects of mitochondrial inhibitors (CN(-), a complex IV inhibitor and CCCP, protonophore) on catecholamine (CA) secretion and mitochondrial function were explored functionally and biochemically in rat and guinea-pig adrenal chromaffin cells. Guinea-pig chromaffin cells conspicuously secreted CA in response to CN(-) or CCCP, but rat cells showed a little, if any, secretory response to either of them. The resting metabolic rates in rat adrenal medullae did not differ from those in guinea-pig adrenal medullae. On the other hand, the time course of depolarization of the mitochondrial membrane potential (ΔΨm) in guinea-pig chromaffin cells in response to CN(-) was slower than that in rat chromaffin cells, and this difference was abolished by oligomycin, an F1F0-ATPase inhibitor. The extent of CCCP-induced decrease in cellular ATP in guinea-pig chromaffin cells, which was indirectly measured using a Mg(2+) indicator, was smaller than that in rat chromaffin cells. Relative expression levels of F1F0-ATPase inhibitor factor in guinea-pig adrenal medullae were smaller than in rat adrenal medullae, and the opposite was true for F1F0-ATPase α subunit. The present results indicate that guinea-pig chromaffin cells secrete more CA in response to a mitochondrial inhibitor than rat chromaffin cells and this higher susceptibility in the former is accounted for by a larger extent of reversed operation of F1F0-ATPase with the consequent decrease in ATP under conditions where ΔΨm is depolarized.

Comparative toxicity and carcinogenicity of soluble and insoluble cobalt compounds.

Occupational exposure to cobalt is of widespread concern due to its use in a variety of industrial processes and the occurrence of occupational disease. Due to the lack of toxicity and carcinogenicity data following exposure to cobalt, and questions regarding bioavailability following exposure to different forms of cobalt, the NTP conducted two chronic inhalation exposure studies in rats and mice, one on soluble cobalt sulfate heptahydrate, and a more recent study on insoluble cobalt metal. Herein, we compare and contrast the toxicity profiles following whole-body inhalation exposures to these two forms of cobalt. In general, both forms were genotoxic in the Salmonella T98 strain in the absence of effects on micronuclei. The major sites of toxicity and carcinogenicity in both chronic inhalation studies were the respiratory tract in rats and mice, and the adrenal gland in rats. In addition, there were distinct sites of toxicity and carcinogenicity noted following exposure to cobalt metal. In rats, carcinogenicity was observed in the blood, and pancreas, and toxicity was observed in the testes of rats and mice. Taken together, these findings suggest that both forms of cobalt, soluble and insoluble, appear to be multi-site rodent carcinogens following inhalation exposure.

Lycium europaeum fruit extract: antiproliferative activity on A549 human lung carcinoma cells and PC12 rat adrenal medulla cancer cells and assessment of its cytotoxicity on cerebellum granule cells.

Cancer is a major worldwide health problem and one of the leading causes of death either in developed or developing countries. Plant extracts and derivatives have always been used for various disease treatments and many anticancer agents issued from plants and vegetables are clinically recognized and used all over the world. Lycium europaeum (Solanaceae) also called "wolfberry" was known since ancient times in the Mediterranean area as a medicinal plant and used in several traditional remedies. The Lycium species capacity of reducing the incidence of cancer and also of halting or reserving the growth of cancer was reported by traditional healers. In this study, the antiproliferative capacity, protective properties, and antioxidant activity of the hydro-alcoholic fruit extract of Lycium europaeum were investigated. Results showed that Lycium extract exhibits the ability to reduce cancer cell viability, inhibits proliferation, and induces apoptosis in A549 human lung cancer cells and PC12 rat adrenal medulla cancer cells, in a concentration- and time-dependent manner. Cytotoxic effect on normal rat cerebellum granule cells was assessed to be nonsignificant. Results also showed that Lycium fruit extract protected lipids, proteins, and DNA against oxidative stress damages induced by H2O2 via scavenging reactive oxygen species.

Melatonin attenuates intermittent hypoxia-induced lipid peroxidation and local inflammation in rat adrenal medulla.

Chronic intermittent hypoxia (CIH) induces lipid peroxidation and leads to cardiovascular dysfunction, in which impaired activities of the adrenal medulla are involved. This may be caused by CIH-induced injury in the adrenal medulla, for which the mechanism is currently undefined. We tested the hypothesis that melatonin ameliorates the CIH-induced lipid peroxidation, local inflammation and cellular injury in rat adrenal medulla. Adult Sprague-Dawley rats were exposed to air (normoxic control) or hypoxia mimicking a severe recurrent sleep apnoeic condition for 14 days. The injection of melatonin (10 mg/kg) or vehicle was given before the daily hypoxic treatment. We found that levels of malondialdehyde and nitrotyrosine were significantly increased in the vehicle-treated hypoxic group, when compared with the normoxic control or hypoxic group treated with melatonin. Also, the protein levels of antioxidant enzymes (superoxide dismutase (SOD)-1 and SOD-2) were significantly lowered in the hypoxic group treated with vehicle but not in the melatonin group. In addition, the level of macrophage infiltration and the expression of inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-1ß and IL-6) and mediators (inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2)) were elevated in the vehicle-treated hypoxic group, but were significantly ameliorated by the melatonin treatment. Moreover, the amount of apoptotic cells in the hypoxic groups was significantly less in the melatonin-treated group. In conclusion, CIH-induced lipid peroxidation causes local inflammation and cellular injury in the adrenal medulla. The antioxidant and anti-inflammatory actions of melatonin are indicative of a protective agent against adrenal damage in patients with severe obstructive sleep apnea syndrome.

Bidirectional regulation of bakuchiol, an estrogenic-like compound, on catecholamine secretion.

Excess or deficiency of catecholamine (CA) secretion was related with several diseases. Recently, estrogen and phytoestrogens were reported to regulate the activity of CA system. Bakuchiol is a phytoestrogen isolated from the seeds of Psoralea corylifolia L. (Leguminosae) which has been used in Traditional Chinese medicine as a tonic or aphrodisiac. In the present study, bovine adrenal medullary cells were employed to investigate the effects and mechanisms of bakuchiol on the regulation of CA secretion. Further, its anti-depressant like and anti-stress effects were evaluated by using behavioral despair and chronic immobilization stress models. Our results indicated that bakuchiol showed bidirectional regulation on CA secretion. It stimulated basal CA secretion in a concentration dependent manner (p<0.01), while it reduced 300µM acetylcholine (ACh) (p<0.01), 100µM veratridine (Ver) (p<0.01) and 56mM K(+) (p<0.05) induced CA secretion, respectively. We also found that the stimulation of basal CA secretion by bakuchiol may act through estrogen-like effect and the JNK pathway in an extra-cellular calcium independent manner. Further, bakuchiol elevated tyrosine hydroxylase Ser40 and Ser31 phosphorylation (p<0.01) through the PKA and ERK1/2 pathways, respectively. Bakuchiol inhibited ACh, Ver and 56mM K(+) induced CA secretion was related with reduction of intracellular calcium rise. In vivo experiments, we found that bakuchiol significantly reduced immobilization time in behavioral despair mouse (p<0.05 or 0.01), and plasma epinephrine (E) and norepinephrine (NE) levels in chronic immobilization stress (p<0.05). Overall, these results present a bidirectional regulation of bakuchiol on CA secretion which indicated that bakuchiol may exert anti-stress and the potential anti-depressant-like effects.

Regulation of α3-containing GABAA receptors in guinea-pig adrenal medullary cells by adrenal steroids.

GABA is thought to function as a paracrine factor in adrenal medullary (AM) cells. Thus, we electrophysiologically and immunologically examined the properties of GABAA receptors (GABAARs) in guinea-pig AM cells. Bath application of GABA produced an inward current at -60 mV in a dose-dependent manner with an EC50 of 32.3 µM. This GABA-induced current was enhanced by allopregnanolone at concentrations of 0.01 µM and more. A prior exposure to allopregnanolone resulted in a decrease in an EC50 for GABA in activating GABAARs. The GABA-induced current was suppressed by Zn(2+) in a dose-dependent manner with an IC50 of 18 µM, whereas it was enhanced by 100 µM La(3+). The benzodiazepine analog diazepam was three times more potent than zolpidem in enhancing the GABA current, and it was also augmented by L-838,417, which has no action on α1-containing GABAARs. The GABAAR α3, but not α1, and γ2 subunits were immunologically detected at the cell periphery. The expression of α3 subunits in PC12 cells was enhanced by glucocorticoid activity. The results indicated that GABAARs in guinea-pig AM cells mainly comprise α3, ß, and γ2 subunits and are enhanced by allopreganalone and glucocorticoids may play a major role in the expression of α3 subunits.

Bradykinin B2 receptor in the adrenal medulla of male rats and mice: glucocorticoid-dependent increase with immobilization stress.

Bradykinin, acting via the bradykinin B2 receptor (B2R), is a potent stimulator of adrenomedullary catecholamine biosynthesis and release and likely plays an important role in the adrenomedullary stress response. However, the effects of stress on the expression of this receptor in the adrenal medulla are currently unclear. Here, we examined the changes in adrenomedullary B2R gene expression in male rats in response to single (1 time) and repeated (6 times) exposure to 2 hours immobilization stress (IMO). Immediately after 1 or 6 times IMO, B2R mRNA levels were increased by 9-fold and 7-fold, respectively, and returned to unstressed control levels 3 hours later. This large, but transient, increase in mRNA elicited a doubling of protein levels 3 hours after the stress exposure. Next, the role of the hypothalamic-pituitary-adrenocortical axis in the stress-induced upregulation of B2R gene expression was examined. Treatment with endogenous (corticosterone) and synthetic (dexamethasone) glucocorticoids dose-dependently increased B2R mRNA levels in adrenomedullary-derived PC12 cells. Furthermore, cortisol supplementation at levels mimicking stress exposure elevated B2R mRNA levels in the adrenal medulla of hypophysectomized rats. In response to 1 exposure to IMO, the stress-triggered rise in plasma corticosterone and adrenomedullary B2R mRNA levels was attenuated in CRH-knockout mice and absent in pharmacologically adrenalectomized rats, indicating a requirement for glucocorticoids in the upregulation of B2R gene expression with stress. Overall, the increase in B2R gene expression in response to the stress-triggered rise in glucocorticoids likely enhances catecholamine biosynthesis and release and may serve as an adaptive response of the adrenomedullary catecholaminergic system to stress.

Lower density of L-type and higher density of P/Q-type of calcium channels in chromaffin cells of hypertensive, compared with normotensive rats.

Enhanced activity of the sympatho-adrenal axis and augmented circulating catecholamines has been implicated in the development of hypertension. Release of catecholamine from stimulated adrenal medulla chromaffin cells has been shown to be higher and longer in spontaneously hypertensive rats (SHRs), compared with normotensive Wistar rats (NWRs). Whether differences in the functional expression of voltage-dependent calcium channels (VDCCs) of the L-, N-, or P/Q subtypes may contribute to such distinct secretory behaviour, is unknown. We therefore approached here this study in voltage-clamped NWR and SHR chromaffin cells, using 10mM Ba(2+) as charge carrier (IBa) and selective blockers of each channel type. We found that compared with NWR cells, SHR chromaffin cells exhibited the following differences: (1) 30% diminution of the IBa fraction carried by L channels; (2) a doubling of the IBa fraction carried by P/Q channels; (3) more visible current modulation by ATP that could be linked to a 10-fold higher mRNA levels for purinergic receptors of the P2Y2 subtype; and (3) a higher contribution of PQ channels to the transients of the cytosolic calcium concentrations ([Ca(2+)]c) generated by K(+), compared with L channels. These results may contribute to the better understanding of the greater calcium signalling and exocytotic responses of SHR compared with NWR chromaffin cells, found in three previous reports from our laboratories.

Pentazocine inhibits norepinephrine transporter function by reducing its surface expression in bovine adrenal medullary cells.

(±)-Pentazocine (PTZ), a non-narcotic analgesic, is used for the clinical management of moderate to severe pain. To study the effect of PTZ on the descending noradrenergic inhibitory system, in the present study we examined the effect of [(3)H]norepinephrine (NE) uptake by cultured bovine adrenal medullary cells and human neuroblastoma SK-N-SH cells. (-)-PTZ and (+)-PTZ inhibited [(3)H]NE uptake by adrenal medullary cells in a concentration-dependent (3-100 µM) manner. Eadie-Hofstee analysis of [(3)H]NE uptake showed that both PTZs caused a significant decrease in the V(max) with little change in the apparent K(m), suggesting non-competitive inhibition. Nor-Binaltorphimine and BD-1047, κ-opioid and σ-receptor antagonists, respectively, did not affect the inhibition of [(3)H]NE uptake induced by (-)-PTZ and (+)-PTZ, respectively. PTZs suppressed specific [(3)H]nisoxetine binding to intact SK-N-SH cells, but not directly to the plasma membranes isolated from the bovine adrenal medulla. Scatchard analysis of [(3)H]nisoxetine binding to SK-N-SH cells revealed that PTZs reduced the B(max) without changing the apparent K(d). Western blot analysis showed a decrease in biotinylated cell-surface NE transporter (NET) expression after the treatment with (-)-PTZ. These findings suggest that PTZ inhibits the NET function by reducing the amount of NET in the cell surface membranes through an opioid and σ-receptor-independent pathway.

Señalización de la angiotensina II, a través de la producción de radicales libres en estructuras del sistema nervioso: papel en el estres agudo y crónico / Angiotensin II signaling, through the production of free radicals in structures of the nervous system: role in acute and chronic stress

Existen evidencias que apoyan la participación de las especies reactivas de oxígeno en las cascadas de señalización y transducción intracelular de la angiotensina II. La ANG II es importante en el mantenimiento de la homeostasis corporal, regulando la presión arterial y el metabolismo de fluidos y electrolitos. Se sabe que en la periferia, la ANG II es capaz de estimular a la NAD(P)H oxidasa con la subsiguiente producción de ERO. El anión superóxido es metabolizado secuencialmente por las enzimas antioxidantes como la superóxido dismutasa, la catalasa y la glutatión peroxidasa. A su vez, las especies reactivas de oxígeno son capaces de activar a las proteínas kinasas activadas por mitógenos, las cuales se encuentran asociadas al crecimiento y la diferenciación celular. Se evaluó la posible participación de las especies reactivas de oxígeno en el mecanismo de señalización intracelular mediado por el receptorAT1en el hipotálamo, el órgano subfornicaly médula suprarrenal de la rata. Nuestros resultados demostraron que la estimulación del tejido nervioso con ANG II in vitroincrementó la actividad de la enzimas antioxidante. Al evaluar el papel del receptor AT1, la NAD(P)H oxidasa, el anión superóxido y la proteína kinasa C; así como la activación de las ERK1/2 en la señalización de la ANG II en el hipotálamo, OSF y MSR, demostramos que el bloqueo del receptor AT1con losartán, la interferencia del ensamblaje de la NAD(P)H oxidasa con apocinina, el secuestro de anión superóxido empleando un mimético de la SOD, tempol,y la inhibición de la PKC con cheleritrina, bloquearon completamente el efecto que produce la ANG II sobre las enzimas antioxidantes in vitro.Igualmente, la activación de la ERK1/2 inducida por la ANG II fue reducida por APO y LOS a nivel hipotalámico. Adicionalmente, el bloqueo del receptor AT2hipotalámico con PD123319, no bloqueo sino que mas bien potenció la respuesta de las enzimas antioxidantes y la activación de las ERK1/2 inducida por la ANG II, lo que desenmascaró el efecto contra regulatorio del receptor AT2sobre la acción de la ANG II mediada por el receptor AT1. Se sabe que durante el estrés el sistema renina angiotensina circulante y cerebral se encuentra estimulado, por lo tanto el incremento de la ANG II endógena debería desencadenar vías de señalización similares a las reportadas in vitro. Efectivamente, nuestros hallazgos demostraron que tanto,el estrés agudo inducido por la inmovilización forzada,como el estrés crónico en ratas espontáneamente hipertensas incrementaron la actividad de las enzimas antioxidantes en las tres estructuras cerebrales estudiadas. Este efecto es mediado por la vía del receptor AT1, la estimulación de la NAD(P)H oxidasa y la producción de anión superóxido ya que el tratamiento in vivo con LOS, APO y TEM fue capaz de bloquear completamente el incremento de la actividad de las enzimas antioxidantes inducidas por el estrés y por ende por la ANG II endógena.A nivel de la MSR demostramos, por primera vez, que la estimulación del receptor AT2 esta asociada a la estimulación de la NAD(P)H oxidasa, ya que la APOy el PD 123319 fueron capaces de bloquear el incremento de la actividad de las enzimas antioxidantes inducida por la ANG II. Demostrando así, que el receptor AT1en la MSR contrarregula la acción de la ANG II a través del receptor AT2.En conclusión, nuestros resultados indican que a nivel del sistema nervioso las especies reactivas de oxígeno participan en la cascada de señalización intracelular de la ANG II, y ejercen un importante papel en la respuesta al estrés y la hipertensión.

Cholinergic stimulation of adrenal medulla is essential for the granulicytopoietic response to lithium.

Granulocytopoietic response to lithium carbonate (Li+) in rat was eliminated completely by N-cholinergic blocking agent, and independently by alpha-1-adrenergic antagonist. A link between these two contradictory events is explained by release of acetylcholine from the cholinergic preganglionic nerve endings in adrenal medulla triggered by Li+, and subsequent discharge of catecholamines (CA) from medullar chromaffin cells, which on their part activate adrenergic receptors of alpha-1 class on hematopoietic progenitor cells. Respectively, granulocytopoietic response to Li+ is blocked by cholinergic N-blocking agent at the level of adrenal medulla, and by the alpha-adrenergic blocking agent at the level of the hematopoietic cells proper. The stimulatory action of Li+ on granulocytopoietic cells is indirect, while is mediated by CA release from adrenal chromaffine cells. At the initial stages of leukocyte restitution in the acute myelotoxic leucopenia relative increase in "large" lymphocyte fraction (Lge) preceding the increment in granulocyte counts is evident. In this fraction of lymphocytes peripheral blood progenitor cells (PBPC) are expected.

H2S induces catecholamine secretion in rat adrenal chromaffin cells.

Hydrogen sulfide (H(2)S) is recognized as an important gaseous signaling molecule in mammalian tissues and exerts its modulating functions of different systems via targeting different ion channels and receptors. H(2)S can be synthesized from l-cysteine by cystathionine ß-synthetase (CBS) or cystathionine γ-lyase (CSE). It has been reported recently that H(2)S can be synthesized and released in rat adrenal medulla chromaffin cells (AMCs) which play a critical role in the regulation of stress response by releasing catecholamine (CA). In the present study, we combined amperometry and whole-cell patch-clamp recording to explore the direct effect of exogenous H(2)S on CA release in AMCs and the underlying ionic mechanism. Amperometry showed that local application of NaHS, the H(2)S donor, evoked CA release from AMCs. Furthermore, the CA secretory response to NaHS was totally blocked by removing extracellular Ca(2+). Whole-cell patch-clamp experiments showed that H(2)S-induced CA release is produced by membrane depolarization generated by an inhibition of Ca(2+)-activated K(+) current [I(K(Ca)) current]. We conclude that H(2)S is capable of directly inducing CA release by inhibiting the I(K(Ca)) current. This conclusion indicates that H(2)S may involve in the response of adrenal medulla to stress by modulating I(K(Ca)) current and CA release in mammalian animals.