Hormonal synchronization of lipopolysaccharide-induced hypothermic response in rats.

BACKGROUND: Recent experimental evidence suggests that lipopolysaccharide (LPS)-induced hypothermia is an adaptive thermoregulatory strategy against immunological challenge in rats. We hypothesized that the hormones which are predominantly responsible for energy homeostasis may have efferent signaling roles for development of the hypothermia. AIM: The aim of the study was to evaluate the changes of hypothalamic-pituitary-thyroid (HPT) and hypothalamic- pituitary-adrenal (HPA) axis hormones, leptin and erythropoietin at various phases of LPS-induced hypothermia such as the initial phase, nadir and the end of the response in blood sampled rats. MATERIAL AND METHODS: Body temperature of adult male albino Wistar rats was recorded by biotelemetry. E. coli O111:B4 LPS (250 µg/kg, ip) was injected alone or with SC-560, a cyclooxygenase-1 selective inhibitor (1 mg/kg, sc). RESULTS: Serum FT4 levels elevated at the initial phase, but FT3 levels decreased at nadir and remained low at the end of the response. Meanwhile, no change was observed in TSH levels. Serum adrenocorticotropic hormone (ACTH) levels reduced at the initial phase and serum corticosterone levels decreased at nadir without any change in serum corticotropin-releasing hormone (CRH) levels throughout the hypothermia. Serum leptin levels increased only at the end of the response. No change was observed in the levels of serum erythropoietin. SC-560 treatment abolished both LPS-induced hypothermia and respective hormonal changes. CONCLUSION: Data suggest that HPT axis hormones may contribute to development of LPS-induced hypothermia in rats. Data also support the view that leptin may have a role for the recovery of hypothermic response.

Formation of interleukin-6 in the brain of the febrile cat: relationship to interleukin-1.

Previous investigations have shown that interleukin-6 (IL-6), unlike other cytokines, is produced in larger amounts in the brain of the febrile animal regardless of the route, peripheral vs. central, of pyrogen administration. In addition, depending on the experimental condition IL-6 production may or may not require the prior induction of interleukin-1 (IL-1). The present study was carried out in the conscious cat to assess the importance of brain-derived IL-6 in the pathogenesis of fever and the interaction at that site between this cytokine and IL-1. IL-6 was detected in cerebrospinal fluid (CSF) collected at rest and its levels increased during the fever to intravenous (i.v.) endotoxin. The IL-6 elevation, but not the fever, was reversed by pretreatment with intracerebroventricular (i.c.v.) IL-1 receptor antagonist (hIL-1ra). Conversely, when pyrogens (endotoxin, IL-1) were given i.c.v., i.c.v. hIL-1ra reduced the fever without altering significantly the associated rise in CSF IL-6. We conclude that IL-6 is formed in brain in response to both i.v. and i.c.v. pyrogens; however, its formation, whether requiring the prior induction of IL-1 or not, does not appear to be critical for the development of the fever. Blood-borne IL-6, unlike brain-derived IL-6, may still play a role in fever as a trigger of signal-transducing mechanisms operating across the blood-brain barrier.

Dopaminergic and serotonergic alterations in the rat brain during ethanol withdrawal: association with behavioral signs.

Changes in dopaminergic and serotonergic levels and metabolites in cerebral cortex, corpus striatum and hippocampus were investigated during the first 6-h of withdrawal in ethanol-dependent Wistar rats. Ethanol was given by a liquid diet for 21 days. The concentration of ethanol was 7.2% (v/v) for the last 15 days of the exposure. After 2, 4 and 6 h of ethanol withdrawal, and after audiogenic stimulus (100 dB for 60 s) at 6 h of ethanol withdrawal, various brain regions were assayed for levels of dopamine (DA), DOPAC, HVA, serotonin (5-HT) and 5-HIAA. Behavioral signs of ethanol withdrawal and blood ethanol levels were also evaluated in other parallel groups of ethanol-dependent rats. Significant decreases in 5-HT levels and significant increases in HVA levels in striatum were found during the first 6 h of ethanol withdrawal and after the audiogenic seizures. In hippocampus, 5-HIAA levels were significantly reduced after 2 h of ethanol withdrawal and after the audiogenic seizures. 5-HIAA levels significantly increased after 2 h of ethanol withdrawal in cerebral cortex. Significant increases in both DA and 5-HT levels were also found in cerebral cortex after the audiogenic seizures. The results suggest that the levels of DA, 5-HT and their metabolites are altered by ethanol withdrawal. Furthermore, this may suggest that DA and 5-HT may be involved in the first 6 h of ethanol withdrawal syndrome in rats.

Effect of ciliary neurotrophic factor on body temperature and cerebrospinal fluid prostanoids in the cat.

It has been proposed that ciliary neurotrophic factor (CNTF) belongs to the group of cytokines causing fever in response to infectious and inflammatory noxae. The present investigation was undertaken in the conscious cat to verify whether CNTF (human type, hCNTF) is pyrogenic when given either intravenously (i.v.) or intracerebroventricularly (i.c.v.) and correlate at the same time body temperature with cerebrospinal fluid (CSF) levels of prostaglandin (PG) E2 (i.e., the putative fever mediator in brain) and thromboxane (TX) B2 (the stable TXA2 byproduct) in untreated vs. treated animals. hCNTF (10 microg/kg i.v.; 1 microg i.c.v.) caused fever by both routes and the increase in body temperature was associated with an upward change in CSF PGE2. Conversely, CSF TXB2 showed no elevation. Similarly unaffected was CSF TXB2 by human interleukin 6 (hIL-6, 1 microg i.c.v.), a cytokine with known pyrogenic and PGE2-promoting actions sharing the signal-transducing mechanism with hCNTF. We conclude that CNTF lends itself to a role in the pathogenesis of fever. The modest PGE2 elevation relatively to other cytokines, specifically hIL-1, is ascribed to the fact that CNTF activates the inducible isoform of arachidonate cyclooxygenase, which is constitutively expressed in brain, without concomitantly promoting the formation of new enzyme.

Polysaccharide mannan components of Candida albicans and Saccharomyces cerevisiae cell wall produce fever by intracerebroventricular injection in rats.

The cell wall mannan components of Candida albicans and Saccharomyces cerevisiae produced hyperthermic responses when injected intracerebroventricularly at doses of 10 microg in rats. Indomethacin treatment (5 mg/kg subcutaneously) completely abolished these responses. Serum interferon-gamma, tumor necrosis factor-alpha and interleukin-1beta levels showed an upward trend during the initial phase of the hyperthermic response induced by S. cerevisiae mannan. Meanwhile, serum levels of these proinflammatory cytokines did not increase at all at the initial phase of C. albicans mannan-induced hyperthermia. Histopathological examination of the brain tissue samples revealed no specific change throughout the parenchyma of rats given either mannan. These results indicate that the polysaccharide mannan components of yeasts, regardless of the pathogenicity, produce a pyrogenic response by a direct injection into the brain in rats. This response is not accompanied by proinflammatory cytokine induction in the periphery.

Inhibition of pentylenetetrazol-induced seizures in rats by prostaglandin D2.

This study was undertaken to evaluate the role of brain PGD2 activity during PTZ induced seizures in rats. Potentiation of endogenous PGD2 activity caused an anti-convulsant effect. Thus, after PGD2 injection (5 microg/icv) the latency of generalized tonic clonic convulsions was prolonged. ZK 118.182, a stable analogue of PGD2, dose-dependently inhibited the incidence and the intensity of seizures when injected at doses of 1-100 ng/icv. But on the other hand, inhibition of PGD2 activity either by a D-type PG receptor antagonist (AH 6809; 50 ng/icv) or by a PGD synthase inhibitor (sodium selenite; 0.2 microg/icv) produced a proconvulsant effect by increasing the incidence and the intensity of the seizures. These findings indicate that endogenous PGD2 activity in the brain may have a specific inhibitory role for the initiation and propagation of PTZ induced seizures in rats.

Antiseizure activity of insulin: insulin inhibits pentylenetetrazole, penicillin and kainic acid-induced seizures in rats.

The present study was undertaken to evaluate the antiseizure activity spectrum of insulin against various behavioral seizure models in rats. Insulin was injected intraperitoneally (i.p.) at a test dose of 1 U/kg. Dextrose (3 g/kg) was administered simultaneously with insulin to counteract its hypoglycemic effect and induce a normoglycemic state. Insulin was found to significantly decrease the incidence, intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by pentylenetetrazole (60 mg/kg i.p.) and significantly decrease the intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by penicillin (2000 U/intracerebrocortical). Insulin was not only found to prolong the latency of all the seizure components but was found to reduce the incidence of focal myoclonic twitches and generalized tonic-clonic convulsions induced by kainic acid (12 mg/kg i.p.) as well. Insulin was shown to be ineffective to suppress ouabain (5 micrograms/intracerebroventricular) induced seizures. These findings indicate that insulin possesses a broad spectrum of antiseizure activity in rats. Interaction with brain Na(+)-K(+)-ATPase has been discussed as a possible mechanism of action.

Effects of different serotypes of Escherichia coli lipopolysaccharides on body temperature in rats.

The effects of Escherichia coli O55:B5, O127:B8, and O111:B4 serotypes' lipopolysaccharides (LPS) on body temperature were investigated in rats. LPSs were injected intraperitoneally at doses of 2, 50, and 250 microg/kg. A multiphasic and no-dose dependent increase in rectal temperature was observed in response to E. coli O55:B5 LPS at all doses, and in response to E. coli O127:B8 LPS at 2 and 50 microg/kg doses. The highest dose of the latter caused a dual change in rectal temperature, in which hypothermia preceded fever. E. coli O111:B4 LPS was either pyrogenic or hypothermic at 2 and 250 microg/kg doses; respectively, whereas a dual response was observed when the 50 microg/kg dose was injected. Although dual responses were observed after administration of all LPSs at 50 microg/kg dose when the body temperature was recorded by biotelemetry, the hypothermia induced by E. coli O55:B5 LPS was significantly smaller. These data suggest that LPSs induce dose and serotype-specific variable changes on body temperature in rats. This variability may be related to the structure of LPSs. The data also indicate that LPS causes hypothermia with or without fever in rats.

Candida albicans and Saccharomyces cerevisiae cell wall mannans produce fever in rats: role of nitric oxide and cytokines.

Mannan components of C. albicans (5 mg/kg, i.p.) and S. cerevisiae (2.5 mg/kg, i.p.) cell walls produced pyrogenic responses which were completely inhibited by indomethacin (5 mg/kg, s.c.) pretreatment in rats. A non-selective NOS inhibitor, L-NAME (10 mg/kg, s.c.), also inhibited the pyrogenic effectiveness of C. albicans mannan, whereas it was ineffective on the fever induced by S. cerevisiae mannan. A selective elevation in the serum TNF-alpha levels was observed at the initial phase of the fever due to S. cerevisiae mannan, whereas there was no significant change on the serum levels of TNF-alpha, IL-1beta and IFN-gamma during the latent period or at the initial phase of the fever induced by C. albicans mannan. Injections of N-linked and/or O-linked oligomannosides of the either mannan did not cause any significant change in the body temperature and serum cytokine levels. These data suggest that the mannan components of C. albicans and S. cerevisiae cell walls produce a prostaglandin-dependent fever in rats. The initial signal for fever seems to be different for each mannan. Data also indicate that integrity of the mannans is necessary for the pyrogenic response.

Iloprost, a stable analogue of PGI2, potentiates the hyperthermic effect of PGE2 in rats.

Centrally mediated effects of iloprost, a stable analogue of PGI2, on rectal temperature have been investigated in conscious rats. ICV administration of iloprost (100-1,000 ng, ICV) produced a dose-dependent, monophasic hyperthermic response that was not inhibited by indomethacin. When injected into the preoptic anterior hypothalamic (POAH) region, iloprost (2-50 ng/POAH) induced a biphasic increase in rectal temperature. While the first phase was inhibited by AH 6809, an E1-type prostaglandin (EP1) receptor antagonist, the second phase was abolished by indomethacin pretreatment. Iloprost was found not to alter rectal temperature when injected into the ventromedial hypothalamic area. Administration of iloprost into the POAH in a dose that had no effect on rectal temperature significantly potentiated the hyperthermic effect of PGE2 (50 ng, ICV). These findings suggest that the pyrogenic effect of iloprost is partly mediated by EP1 receptors located on the POAH. Regarding the similarities of iloprost and PGI2, it is further proposed that endogenous PGI2 might act to modulate hyperthermic effect of PGE2 released during arachidonic acid- or endogenous pyrogen-induced fever.

Effects of bromocriptine and haloperidol on ethanol withdrawal syndrome in rats.

The effects of bromocriptine and haloperidol, either alone or in combination, on ethanol withdrawal syndrome (EWS) have been investigated in rats. Bromocriptine (5 mg/kg 1P) inhibited wet dog shakes behavior and catatonia but potentiated the intensity of abnormal gait. The latency of the audiogenic seizures was prolonged by bromocriptine treatment. Haloperidol (0.5 mg/kg SC) decreased the intensity of stereotyped behavior but potentiated catatonia and agitation. It did not antagonize the behaviors induced by bromocriptine when injected in combination except the increased latency of the audiogenic seizures. The total intensity score of the EWS was not significantly different from that in untreated control. The results suggest that brain dopaminergic system may be involved to a limited extent in mediating the EWS in rats.

Effects of intracerebral iloprost injections on motor activity and chemically-induced seizures in rats.

The effects of iloprost, a chemically stable analog of prostacyclin, on motor activity, pentylenetetrazol (PTZ)- and strychnine (ST)-induced seizures were studied in rats. Depression on motor activity was observed after a 500 ng/icv dose. Thus, both spontaneous locomotor activity and exploratory behavior were significantly reduced. While iloprost was ineffective against ST-induced seizures, it produced dose-dependent inhibition of PTZ-induced seizures. ED50 (95% confidence limits) value of iloprost for the suppression of clonic convulsions induced by PTZ was 224.96 (100.43-504.00) ng/icv. Anticonvulsive effect of iloprost was significantly potentiated by clonazepam pretreatment. In this case ED50 of iloprost was 39.40 (23.88-65.01) ng/icv. Unilateral iloprost injections into substantia nigra pars reticulata in a relatively lower dose range (0.5-2.0 ng/ic) also dose-dependently inhibited PTZ-induced seizures. In comparison to other prostanoids iloprost seems to have more potent and selective anticonvulsive activity against PTZ-induced seizures without marked motor depressant action in rats. It is further suggested that antiseizure effect of iloprost might be mediated by GABAergic inhibitory mechanisms.

Iloprost-induced writhing in mice and its suppression by morphine.

Intraperitoneally (i.p.) administered iloprost produced a writhing response indicating nociception. This effect induced by 4 micrograms/kg iloprost was dose dependently protected by morphine with an ED50 (95% confidence limits) value of 0.039 (0.0018-0.067) mg/kg. On the other hand, indomethacin had no effect on iloprost-induced writhing. Thus, this effect of iloprost seems to be relatively more sensitive than other irritants-induced responses on determining the analgesic potency of narcotic drugs.

Antiischemic effect of ZK-118.182 in rabbits: a comparative study with iloprost.

The effects of ZK-118.182, a stable analogue of PGD2, were evaluated in an endothelin-1-induced cerebral ischemia rabbit model. Ischemia was induced by endothelin-1 injection (0.25 ng bolus) into subcavian artery and ischemic changes were assessed histologically by the number of ischemic neurons in the brain stem. ZK-118.182 (2 micrograms/kg, bolus into subclavian artery) reduced the number of ischemic neurons when injected 20 min after endothelin-1 injection, Iloprost, a stable analogue of PGI2, was also effective in reducing the number of ischemic neurons in a dose of 0.5 microgram/kg (bolus into subclavian artery). The results suggested that ZK-118.182 has a potent antiischemic effect which is comparable to that of iloprost in rabbits.

An unexpected potent positive chronotropic effect of (15S)-15-methyl-prostaglandin E1 in the isolated guinea-pig right atria.

The effects of (15S)-15-methyl-prostaglandin E1, a synthetic analog of PGE1, other stable prostaglandins, histamine and noradrenaline were studied on the isolated spontaneously beating right atria from guinea-pig, rat and rabbit. When compared with other prostaglandins, histamine and noradrenaline, 15-methyl analog of PGE1 has the most potent positive chronotropic effect and the highest affinity as indicated by a significantly higher pD2 value as compared to other tested analogs in the isolated guinea-pig right atria. Neither the 15-methyl analog of PGE1 nor other stable prostaglandins induced any effect on the atria from rat and rabbit when relatively higher concentrations were used. 15-Methyl-PGE1 did not induce a positive inotropic effect. The maximum positive chronotropic response to 15-methyl-PGE1 was found to be about 60% of that of noradrenaline and histamine but almost equal to that of PGE1. These results were taken as evidence that 15-methyl-PGE1 has an unexpected potent positive chronotropic effect on the isolated spontaneously beating guinea-pig right atrium. The possible mechanism of the action of 15-methyl-PGE1 are discussed.

Effects of flumazenil on ethanol withdrawal syndrome in rats.

Effects of flumazenil (Ro 15-1788, CAS 78755-81-4) on ethanol withdrawal syndrome (EWS) has been investigated in rats. Behavioral EWS symptoms appeared during the first 6 h of ethanol withdrawal. Flumazenil (2.5 and 10 mg/kg i.p.) increased horizontal and vertical locomotor activity significantly and also precipitated abnormal gait and agitation at the beginning of EWS in a dose dependent manner. However, thereafter it reduced the severity of abnormal posture and gait, tail stiffness, agitation and stereotyped behavior in a dose dependent manner. At the 6th hour of EWS, flumazenil (10 mg/kg) reduced total EWS score significantly, but shortened the latency of audiogenic seizures and increased the severity of wet dog shakes. Flumazenil (2.5 and 10 mg/kg) did not elicit behavioral EWS symptoms and audiogenic seizures in non-dependent (control) rats. It did not cause any significant change on locomotor activities in these groups. According to those results, certain actions of flumazenil on the experimental EWS may suggest a potential beneficial effect of this drug in the treatment of EWS in alcoholics, but its enhancing effects on some behavioral EWS symptoms and a potential proconvulsant activity may be a drawback for its use in the treatment of EWS.

Effects of chronic ethanol administration on serotonin metabolism in the various regions of the rat brain.

Changes in serotonin (5-HT) and 5-hydroxy indole acetic acid (5-HIAA), its major metabolite, in cerebral cortex, corpus striatum and hippocampus were investigated at 10th and 21st days of chronic ethanol ingestion in Wistar rats. Ethanol (7.2% v/v) was given to rats in a modified liquid diet. Biochemical analysis was performed in two groups of ethanol-treated and control rats (n = 6 for each group). Rats in each group were decapitated at the 10th and 21st days of ethanol consumption. Brains were removed and cerebral cortex, corpus striatum and hippocampus were dissected. 5-HT and 5-HIAA levels were measured in respective brain regions by using high performance liquid chromatography. In cerebral cortex and corpus striatum, 5-HT levels were significantly lower than control at the 10th day of ethanol consumption. At the 21st day, the levels tended to remain low, but not significantly different statistically. In hippocampus, 5-HIAA levels were significantly higher than control at 10th day of ethanol consumption. Increased 5-HIAA level returned to control values at the 21 st day of ethanol consumption. Our results suggest that, 5-HT clearly seems to play a critical role in the brain at the 10th day of chronic ethanol consumption.

Behavioural assessment of pinealectomy and foetal pineal gland transplantation in rats: Part II.

Pineal gland is an endocrine organ which exerts regulatory effects on the activity of various organs and systems. The present study was undertaken to highlight in experimental animals the possible integrative function of this endocrine organ on a behavioural pattern. Pinealectomy and foetal pineal gland transplantation to a subpial cortical area close to the pinealectomized region was performed. Behaviour was defined through motor activity induced by low (2 mg/kg) and high (10 mg/kg) doses of amphetamine in rats. It was shown that pinealectomy produced significant different patterns of behaviour induced by low and high doses of amphetamine. In sham operated animals low dose amphetamine induced a significant locomotor stimulation but without stereotyped activity. High dose amphetamine induced stereotyped activity. After pinealectomy even low dose amphetamine produced the behavioural pattern of stereotyped activity resembling a high dose amphetamine-induced behaviour. This differential effect of amphetamine, seen in pinealectomized rats, was completely restored after transplantation. On the other hand, melatonin treatment did not generate a significant alteration of behavioural profile either in the control or pinealectomized group of rats. Results are discussed with regard to the general regulatory function of the pineal gland.

Complement (C3, C4) and C-reactive protein responses to cardiopulmonary bypass and protamine administration.

Complement activation has been deemed responsible for the damaging effects of cardiopulmonary bypass (CPB) in patients undergoing open heart surgery. We studied C3, C4 and C-reactive protein (CRP) in 22 patients undergoing CPB. In Group 1 (11 patients), protamine was given intravenously and in Group 2 (11 patients), via the aortic root after CPB. Significant decreases were observed in C3 and C4 during CPB in both groups indicating complement activation primarily by the classic pathway. Protamine did not lead to further activation of the complement system. In both groups, C3 levels gradually returned toward baseline within 24 hours but C4 levels were still lower than baseline 24 hours postoperatively. CPB and protamine administration did not cause any significant changes in CRP levels, but CRP increased abruptly 24 hours after operation. Although activation of complement system during CPB is expected to invoke an acute phase response, we conclude that this period is not long enough to induce an increased production of CRP in response to tissue injury or inflammation.