Differential Role of Neurohypophysial Hormones in Hypotension and Nitric Oxide Production During Endotoxaemia.

Besides their well-established endocrine roles, vasopressin and oxytocin are also important regulators of immune function, participating in a complex neuroendocrine-immune network. In the present study, we investigated whether and how vasopressin and oxytocin could modulate lipopolysaccharide (LPS)-induced nitric oxide (NO) production in a well-established model of experimental endotoxaemia. Male Wistar rats were previously treated i.v. with vasopressin V1 or oxytocin receptor antagonists and then received either an i.v. LPS injection to induce endotoxaemia or a saline imjection as a control. The animals were divided into two groups: in the first group, blood was collected at 2, 4 and 6 h after LPS injection; in the second group, mean arterial blood pressure (MABP) and heart rate (HR) were recorded over 6 h. Plasma vasopressin and oxytocin values were higher in LPS- compared to saline-injected animals at 2 and 4 h but returned to basal levels at 6 h. NO levels exhibited an opposite pattern, showing a progressive increase over the entire period. The previous administration of a vasopressin V1 receptor antagonist significantly reduced NO plasma concentrations at 2 and 4 h but not at 6 h. By contrast, oxytocin receptor agonist pre-treatment had no effect on the NO plasma concentration. In relation to MABP, previous treatment with vasopressin V1 receptor antagonist reversed the LPS-induced hypotension at 4 h, although this was not the case for oxytocin antagonist-treated animals. None of the antagonists affected HR. Our findings indicate that vasopressin (but not oxytocin) has effects on NO production during endotoxaemia in rats, although they do not lend support to the proposed anti-inflammatory actions of vasopressin during endotoxaemia.

Interaction between the carbon monoxide and nitric oxide pathways in the locus coeruleus during fever.

We have documented that the locus coeruleus (LC), the main noradrenergic nucleus in the brain, is part of a thermoeffector neuronal pathway in fever induced by lipopolysaccharide (LPS). Following this pioneering study, we have investigated the role of the LC carbon monoxide (CO) and nitric oxide (NO) pathways in fever. Interestingly, despite both CO and NO are capable of activating the same intracellular target, soluble guanylate cyclase (sGC), our data have shown that LC CO is an antipyretic molecule, whereas LC NO is propyretic. Thus, aiming at further exploring the mechanisms underlying their anti- and propyretic properties, we investigated the putative interplay between the LC CO and NO pathways. Male Wistar rats were implanted with a guide cannula in the fourth ventricle (4V) and a temperature datalogger capsule in the peritoneal cavity. The animals were microinjected into the 4V with an inhibitor of heme oxygenase (HO) (ZnDPBG [zinc(II)deuteroporphyrin IX 2,4 bis ethylene glycol]), or a CO donor (CORM-2 [tricarbonyldichlororuthenium-(II)-dimer]), or an inhibitor of nitric oxide synthase (NOS) (l-NMMA [N(G)-monomethyl-L-arginine acetate]), or an NO donor (NOC12 [3-ethyl-3-(ethylaminoethyl)-1-hydroxy-2-oxo-1-triazene]), and injected with LPS (100 µg/kg i.p.). Two hours later, the rats were decapitated, and the brains were frozen and cut in a cryostat. LC punches were processed to assess LC bilirubin and nitrite/nitrate (NOx) levels. Microinjection of ZnDPBG reduced LC bilirubin and increased LC NOx, whereas l-NMMA diminished LC NOx and reduced LC bilirubin. Furthermore, NOC12 caused an increase in LC bilirubin, whereas CORM-2 caused a reduction in LC NOx. These findings are consistent with the notion that in the LC during LPS fever the CO pathway downmodulates NOS activity and the NO pathway upmodulates HO activity, and, together with previous data, allow us to conjecture that LC CO blunts fever by downmodulating NOS (antipyretic property), LC NO upmodulates HO and sGC activities favoring the development of LPS fever (propyretic effect).

Hydrogen sulfide as a cryogenic mediator of hypoxia-induced anapyrexia.

Hypoxia causes a regulated decrease in body temperature (Tb), a response that has been aptly called anapyrexia, but the mechanisms involved are not completely understood. The roles played by nitric oxide (NO) and other neurotransmitters have been documented during hypoxia-induced anapyrexia, but no information exists with respect to hydrogen sulfide (H(2)S), a gaseous molecule endogenously produced by cystathionine ß-synthase (CBS). We tested the hypothesis that H(2)S production is enhanced during hypoxia and that the gas acts in the anteroventral preoptic region (AVPO; the most important thermosensitive and thermointegrative region of the CNS) modulating hypoxia-induced anapyrexia. Thus, we assessed CBS and nitric oxide synthase (NOS) activities [by means of H(2)S and nitrite/nitrate (NO(x)) production, respectively] as well as cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) levels in the anteroventral third ventricle region (AV3V; where the AVPO is located) during normoxia and hypoxia. Furthermore, we evaluated the effects of pharmacological modifiers of the H(2)S pathway given i.c.v. or intra-AVPO. I.c.v. or intra-AVPO microinjection of CBS inhibitor caused no change in Tb under normoxia but significantly attenuated hypoxia-induced anapyrexia. During hypoxia there were concurrent increases in H(2)S production, which could be prevented by CBS inhibitor, indicating the endogenous source of the gas. cAMP concentration, but not cGMP and NO(x), correlated with CBS activity. CBS inhibition increased NOS activity, whereas H(2)S donor decreased NO(x) production. In conclusion, hypoxia activates H(2)S endogenous production through the CBS-H(2)S pathway in the AVPO, having a cryogenic effect. Moreover, the present data are consistent with the notion that the two gaseous molecules, H(2)S and NO, play a key role in mediating the drop in Tb caused by hypoxia and that a fine-balanced interplay between NOS-NO and CBS-H(2)S pathways takes place in the AVPO of rats exposed to hypoxia.

Role of dexamethasone on vasopressin release during endotoxemic shock.

The present study was designed to assess the hypothesis that dexamethasone (DEX) through the control of nitric oxide (NO) synthesis could regulate the release of vasopressin (AVP), which plays an important role in the regulation of arterial pressure and plasma osmolality. Endotoxemic shock was induced by intravenous (i.v.) injection of 1.5 mg/kg lipopolisaccharide (LPS) in male Wistar rats weighing 250-300 g. After LPS administration, a group of animals were treated with DEX (1.0 mg/kg of body weight), whereas saline-injected rats served as controls. The LPS administration induced a significant decrease in mean arterial pressure (MAP) with a concomitant increase in heart rate (HR) (Delta VMAP: -16.1+/-4.2 mm Hg; Delta VHR: 47.3+/-8.1 bpm). An increase in plasma AVP concentration occurred and was present for 2 h after LPS administration (11.1+/-0.9 pg/mL) returning close to basal levels thereafter and remaining unchanged until the end of the experiment. When LPS was combined with i.v. administration of a low dose of DEX, we observed an attenuation in the drop of MAP (Delta VMAP: -2.2+/-1.9 mm Hg) and a decrease in NO plasma concentration [NO] after LPS administration (1098.1+/-68.1 microM) compared to [NO] after DEX administration (523.4+/-75.2 microM). However, this attenuation in the drop of MAP was accompanied by a decrease in AVP plasma concentration (3.7+/-0.4 pg/mL). These data suggest that AVP does not participate in the recovery of MAP when DEX is administered in this endotoxemic shock model.