Hypotensive acute effect of photobiomodulation therapy on hypertensive rats.

The purpose of this study was to evaluate the acute effect of photobiomodulation therapy (PBM) on arterial pressure in hypertensive and normotensive rats with application in an abdominal region. Normotensive (2K) and hypertensive (2K-1C) wistar rats were treated with PBM. Systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP) and heart rate (HR) were measured before, during and after PBM application. The nitric oxide (NO) serum concentration was measured before and after PBM application. Vascular reactivity study was performed in isolated thoracic aortas. Aluminum gallium arsenide (GaAlAs) diode laser was used, at 660nm wavelength and 100mW optical output. The PBM application induced a decrease of SAP in 2K-1C rats. In 2K rats, the PBM application had no effect on SAP, DAP and MAP. Moreover, the magnitude of hypotensive effect was higher in 2K-1C than in 2K rats. The PBM application induced a decrease of HR in 2K-1C and 2K, with higher effect in 2K-1C rats. In 2K-1C, the hypotensive effect induced by PBM was longer than that obtained in 2K rats. PBM application induced an elevation of NO concentration in serum from 2K-1C and 2K rats, with higher effect in 2K-1C. In isolated aortic rings PBM effect is dependent of NO release, and is not dependent of nitric oxide synthase (NOS) activation. Our results indicate that the abdominal acute application of PBM at 660nm is able to induce a long lasting hypotensive effect in hypertensive rats and vasodilation by a NO dependent mechanism.

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.

Endogenous preoptic hydrogen sulphide attenuates hypoxia-induced hyperventilation.

AIM: We hypothesized that hydrogen sulphide (H2 S), acting specifically in the anteroventral preoptic region (AVPO - an important integrating site of thermal and cardiorespiratory responses to hypoxia in which H2 S synthesis has been shown to be increased under hypoxic conditions), modulates the hypoxic ventilatory response. METHODS: To test this hypothesis, we measured pulmonary ventilation (V˙E) and deep body temperature of rats before and after intracerebroventricular (icv) or intra-AVPO microinjection of aminooxyacetate (AOA; CBS inhibitor) or Na2 S (H2 S donor) followed by 60 min of hypoxia exposure (7% O2 ). Furthermore, we assessed the AVPO levels of H2 S of rats exposed to hypoxia. Control rats were kept under normoxia. RESULTS: Microinjection of vehicle, AOA or Na2 S did not change V˙E under normoxic conditions. Hypoxia caused an increase in ventilation, which was potentiated by microinjection of AOA because of a further augmented tidal volume. Conversely, treatment with Na2 S significantly attenuated this response. The in vivo H2 S data indicated that during hypoxia the lower the deep body temperature the smaller the degree of hyperventilation. Under hypoxia, H2 S production was found to be increased in the AVPO, indicating that its production is responsive to hypoxia. The CBS inhibitor attenuated the hypoxia-induced increase in the H2 S synthesis, suggesting an endogenous synthesis of the gas. CONCLUSION: These data provide solid evidence that AVPO H2 S production is stimulated by hypoxia, and this gaseous messenger exerts an inhibitory modulation of the hypoxic ventilatory response. It is probable that the H2 S modulation of hypoxia-induced hyperventilation is at least in part in proportion to metabolism.

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.

Estradiol and thermoregulation in adult endotoxemic rats exposed to lipopolysaccharide in neonatal life.

AIMS: Early life immune challenge has been considered an adaptive defense strategy against potential pathogens when the innate immune system is not completely developed. This study assesses whether neonatal endotoxin challenge alters body temperature response in adult female rats during endotoxemic shock and also, whether ovarian hormones may participate in this response. METHODS: Rats were intraperitoneally injected with lipopolysacharide (LPS) or saline at post-natal day 14, then as adults they were submitted to endotoxemic shock. RESULTS: The LPS injection in adult neonatal Saline rats caused an initial hypothermia, followed by a febrile response. However, neonatal LPS showed an increased hypothermic response and an attenuation of fever. The bilateral ovariectomy abolished the difference in body temperature between the neonatal LPS and saline rats. To determine the dependence of ovarian hormones, ovariectomized rats treated with estradiol cypionate (ECP) restored hypothermia and the suppressed febrile response. However, the same results were not obtained when the animals were supplemented with ECP and medroxyprogesterone acetate (MPA). The neonatal LPS rats displayed a significant reduction in TNF-α levels and an increase in IL-10 levels when compared with saline animals. The ECP injection significantly enhanced IL-10 and suppressed TNF-α in neonatal LPS, but it did not change the inflammatory response in the saline rats. The ECP + MPA regiment in the neonatal LPS rats reduced TNF-α, but eliminated IL-10 stimulation in comparison with the saline group. CONCLUSION: The present investigation shows that neonatal LPS challenge alters the thermoregulatory response during endotoxemic shock in adulthood and the mechanism for this difference could be mediated by sex hormones, especially estradiol.

Role of brain nitric oxide in the thermoregulation of broiler chicks.

Nitric oxide (NO) plays a key role in body temperature (Tb) regulation of mammals, acting on the brain to stimulate heat loss. Regarding birds, the putative participation of NO in the maintenance of Tb in thermoneutrality or during heat stress and the site of its action (periphery or brain) is unknown. Thus, we tested if NO participates in the maintenance of chicks' Tb in those conditions. We investigated the effect of intramuscular (im; 25, 50, 100mg/kg) or intracerebroventricular (icv; 22.5, 45, 90, 180 microg/animal) injections of the non selective NO synthase inhibitor L-NAME on Tb of 5-day-old chicks at thermoneutral zone (TNZ; 31-32 degrees C) and under heat stress (37 degrees C for 5-6h). We also verified plasma and diencephalic nitrite/nitrate levels in non-injected chicks under both conditions. At TNZ, 100mg/kg (im) or 45, 90, 180 microg (icv) of L-NAME decreased Tb. A significant correlation between Tb and diencephalic, but not plasma, nitrite/nitrate levels was observed. Heat stress-induced hyperthermia was inhibited by all tested doses of L-NAME (im and icv). Tb was correlated neither with plasma nor with diencephalic nitrite/nitrate levels during heat stress. These results indicate the involvement of brain NO in the maintenance of Tb of chicks, an opposite action of that observed in mammals, and may modulate hyperthermia.

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.

Neuro-immune-endocrine mechanisms during septic shock: role for nitric oxide in vasopressin and oxytocin release.

Septic shock is a major cause of death following trauma and a persistent problem in surgical patients. It is a challenge to the critical care medicine specialist and carries an unacceptably high mortality rate, despite adequate antibiotic and vasopressor therapy. The prevalent hypothesis regarding its mechanism is that the syndrome is caused by an excessive defensive and inflammatory response. During the acute phase some signalling mechanisms are activated, particularly hormone release, which function to restore the host homeostasis that has been disturbed by the infection. Since the neuroendocrine and immune systems are functionally related, so the exposure to antigens induces a synchronized response, which allows the organism to successfully endure immunology changes. An important characteristic of this communication includes the appearance of proteins released into the circulation by activated immune cells. These proteins, called cytokines can enter the circulation and reach neuroendocrine organs, where they act either themselves or through the release of intermediates such as prostaglandin, catecholamines and nitric oxide. The synthesis of nitric oxide may be induced in brain as a consequence of infection and may alter the function of the hypothalamic-pituitary axis. In this review we discuss the physiologic roles of the nitric oxide in central nervous system controlling the regulation of vasopressin and oxytocin during the pathophysiology of sepsis.

Nitrergic modulation of vasopressin, oxytocin and atrial natriuretic peptide secretion in response to sodium intake and hypertonic blood volume expansion.

The central nervous system plays an important role in the control of renal sodium excretion. We present here a brief review of physiologic regulation of hydromineral balance and discuss recent results from our laboratory that focus on the participation of nitrergic, vasopressinergic, and oxytocinergic systems in the regulation of water and sodium excretion under different salt intake and hypertonic blood volume expansion (BVE) conditions. High sodium intake induced a significant increase in nitric oxide synthase (NOS) activity in the medial basal hypothalamus and neural lobe, while a low sodium diet decreased NOS activity in the neural lobe, suggesting that central NOS is involved in the control of sodium balance. An increase in plasma concentrations in vasopressin (AVP), oxytocin (OT), atrial natriuretic peptide (ANP), and nitrate after hypertonic BVE was also demonstrated. The central inhibition of NOS by L-NAME caused a decrease in plasma AVP and no change in plasma OT or ANP levels after BVE. These data indicate that the increase in AVP release after hypertonic BVE depends on nitric oxide production. In contrast, the pattern of OT secretion was similar to that of ANP secretion, supporting the view that OT is a neuromodulator of ANP secretion during hypertonic BVE. Thus, neurohypophyseal hormones and ANP are secreted under hypertonic BVE in order to correct the changes induced in blood volume and osmolality, and the secretion of AVP in this particular situation depends on NOS activity.

Nitrergic modulation of vasopressin, oxytocin and atrial natriuretic peptide secretion in response to sodium intake and hypertonic blood volume expansion

The central nervous system plays an important role in the control of renal sodium excretion. We present here a brief review of physiologic regulation of hydromineral balance and discuss recent results from our laboratory that focus on the participation of nitrergic, vasopressinergic, and oxytocinergic systems in the regulation of water and sodium excretion under different salt intake and hypertonic blood volume expansion (BVE) conditions. High sodium intake induced a significant increase in nitric oxide synthase (NOS) activity in the medial basal hypothalamus and neural lobe, while a low sodium diet decreased NOS activity in the neural lobe, suggesting that central NOS is involved in the control of sodium balance. An increase in plasma concentrations in vasopressin (AVP), oxytocin (OT), atrial natriuretic peptide (ANP), and nitrate after hypertonic BVE was also demonstrated. The central inhibition of NOS by L-NAME caused a decrease in plasma AVP and no change in plasma OT or ANP levels after BVE. These data indicate that the increase in AVP release after hypertonic BVE depends on nitric oxide production. In contrast, the pattern of OT secretion was similar to that of ANP secretion, supporting the view that OT is a neuromodulator of ANP secretion during hypertonic BVE. Thus, neurohypophyseal hormones and ANP are secreted under hypertonic BVE in order to correct the changes induced in blood volume and osmolality, and the secretion of AVP in this particular situation depends on NOS activity

Role of neuronal nitric oxide synthase in hypoxia-induced anapyrexia in rats.

Anapyrexia (a regulated decrease in body temperature) is a response to hypoxia that occurs in organisms ranging from protozoans to mammals, but very little is known about the mechanisms involved. Recently, it has been shown that the NO pathway plays a major role in hypoxia-induced anapyrexia. However, very little is known about which of the three different nitric oxide synthase isoforms (neuronal, endothelial, or inducible) is involved. The present study was designed to test the hypothesis that neuronal nitric oxide synthase (nNOS) plays a role in hypoxia-induced anapyrexia. Body core temperature (T(c)) of awake, unrestrained rats was measured continuously using biotelemetry. Rats were submitted to hypoxia, 7-nitroindazole (7-NI; a selective nNOS inhibitor) injection, or both treatments together. Control animals received vehicle injections of the same volume. We observed a significant (P < 0.05) reduction in T(c) of approximately 2.8 degrees C after hypoxia (7% inspired O(2)), whereas intraperitoneal injection of 7-NI at 25 mg/kg caused no significant change in T(c). 7-NI at 30 mg/kg elicited a reduction in T(c) and was abandoned in further experiments. When the two treatments were combined (25 mg/kg of 7-NI and 7% inspired O(2)), we observed a significant attenuation of hypoxia-induced anapyrexia. The data indicate that nNOS plays a role in hypoxia-induced anapyrexia.

Antipyretic effect of arginine vasotocin in toads.

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an important antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a temperature probe were placed in a thermal gradient, and preferred body temperature was recorded continuously. A behavioral fever was observed after lipopolysaccharide (LPS) was injected systemically (200 microg/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temperature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT (10 pmol/kg), which did not affect LPS-induced fever when injected peripherally, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion that AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.

[Therapeutic use of nitric oxide: implications for nursing]. / Utilização do óxido nítrico como terapêutica: implicações para a enfermagem.

Nitric oxide (NO) is a gas that transmits signals in the organism. Such signal transmission takes place by means of the gas synthesis and release in different cell types. After it is released, the gas penetrates the membrane of a neighboring cell and regulates its function. Such mechanism represents an entirely new signaling principle in biological systems. The discoverers of NO as a signaling molecule were awarded the Nobel Prize in Medicine and Physiology in 1998. This discovery has revolutionized medicine and originated new treatments for old problems. In this study, we review the role of NO in some pathologies such as sepsis, arterial hypertension and pulmonary hypertension and Nitric Oxide is explained in terms of its current merit for treatment and its impact on nursing care.

Role of nitric oxide in hypoxia inhibition of fever.

Hypoxia causes a regulated decrease in body temperature (T(b)), and nitric oxide (NO) is now known to participate in hypoxia-induced hypothermia. Hypoxia also inhibits lipopolysaccharide (LPS)-induced fever. We tested the hypothesis that NO may participate in the hypoxia inhibition of fever. The rectal temperature of awake, unrestrained rats was measured before and after injection of LPS, with or without concomitant exposure to hypoxia, in an experimental group treated with N(omega)-nitro-L-arginine (L-NNA) for 4 consecutive days before the experiment and in a saline-treated group (control). L-NNA is a nonspecific NO synthase inhibitor that blocks NO production. LPS caused a dose-dependent typical biphasic rise in T(b) that was completely prevented by hypoxia (7% inspired oxygen). L-NNA caused a significant drop in T(b) during days 2-4 of treatment. When LPS was injected into L-NNA-treated rats, inhibition of fever was observed. Moreover, the effect of hypoxia during fever was significantly reduced. The data indicate that the NO pathway plays a role in hypoxia inhibition of fever.

Tolerance to lipopolysaccharide is related to the nitric oxide pathway.

Repeated administration of lipopolysaccharide (LPS) induces a refractory state to its usual pyrogenic effects which is called endotoxin tolerance. We tested the hypothesis that nitric oxide (NO) participates in the endotoxin tolerance. Single injection of LPS resulted in an elevation in body temperature (Tb), whereas a significant reduction of the thermoregulatory response to LPS was observed to repeated administration of LPS (administered at 48 h intervals). Intracerebroventricular (i.c.v.) injection of L-NAME (a non-selective NO inhibitor of nitric oxide synthesis) markedly enhanced the febrile response to LPS in tolerant rats. The data suggest that NO pathway in the central nervous system plays a role in endotoxin tolerance.

Role of nitric oxide in 2-deoxy-D-glucose-induced hypothermia in rats.

The present study was designed to test the hypothesis that nitric oxide (NO) plays a role in 2-deoxy-D-glucose (2-DG)-induced hypothermia. The body temperature of awake, unrestrained rats was measured before and after the administration of 2-DG, or N(G)-nitro-L-arginine methyl ester (L-NAME; a non-selective NOS inhibitor) or both treatments together. We observed a significant reduction in body temperature after 2-DG injection. L-NAME alone caused no significant change in body temperature. When the two treatments were combined, a reduction in the magnitude of 2-DG-induced hypothermia was observed. The neuronal NOS inhibitor 7-nitroindazole also inhibited 2-DG-induced hypothermia. The data indicate that NO, probably produced by neuronal NOS, plays a role in 2-DG-induced hypothermia.

Effects of a neuronal nitric oxide synthase inhibitor on lipopolysaccharide-induced fever.

It has been demonstrated that nitric oxide (NO) has a thermoregulatory action, but very little is known about the mechanisms involved. In the present study we determined the effect of neuronal nitric oxide synthase (nNOS) inhibition on thermoregulation. We used 7-nitroindazole (7-NI, 1, 10 and 30 mg/kg body weight), a selective nNOS inhibitor, injected intraperitoneally into normothermic Wistar rats (200-250 g) and rats with fever induced by lipopolysaccharide (LPS) (100 microg/kg body weight) administration. It has been demonstrated that the effects of 30 mg/kg of 7-NI given intraperitoneally may inhibit 60% of nNOS activity in rats. In all experiments the colonic temperature of awake unrestrained rats was measured over a period of 5 h at 15-min intervals after intraperitoneal injection of 7-NI. We observed that the injection of 30 mg/kg of 7-NI induced a 1.5 degrees C drop in body temperature, which was statistically significant 1 h after injection (P<0.02). The coinjection of LPS and 7-NI was followed by a significant (P<0.02) hypothermia about 0.5 degrees C below baseline. These findings show that an nNOS isoform is required for thermoregulation and participates in the production of fever in rats.

Effects of a neuronal nitric oxide synthase inhibitor on lipopolysaccharide-induced fever

It has been demonstrated that nitric oxide (NO) has a thermoregulatory action, but very little is known about the mechanisms involved. In the present study we determined the effect of neuronal nitric oxide synthase (nNOS) inhibition on thermoregulation. We used 7-nitroindazole (7-NI, 1, 10 and 30 mg/kg body weight), a selective nNOS inhibitor, injected intraperitoneally into normothermic Wistar rats (200-250 g) and rats with fever induced by lipopolysaccharide (LPS) (100 µg/kg body weight) administration. It has been demonstrated that the effects of 30 mg/kg of 7-NI given intraperitoneally may inhibit 60 per cent of nNOS activity in rats. In all experiments the colonic temperature of awake unrestrained rats was measured over a period of 5 h at 15-min intervals after intraperitoneal injection of 7-NI. We observed that the injection of 30 mg/kg of 7-NI induced a 1.5oC drop in body temperature, which was statistically significant 1 h after injection (P<0.02). The coinjection of LPS and 7-NI was followed by a significant (P<0.02) hypothermia about 0.5oC below baseline. These findings show that an nNOS isoform is required for thermoregulation and participates in the production of fever in rats.

Endogenous vasopressin does not mediate hypoxia-induced anapyrexia in rats.

The present study was designed to test the hypothesis that arginine vasopressin (AVP) mediates hypoxia-induced anapyrexia. The rectal temperature of awake, unrestrained rats was measured before and after hypoxic hypoxia, AVP-blocker injection, or a combination of the two. Control animals received saline injections of the same volume. Basal body temperature was 36.52 +/- 0.29 degreesC. We observed a significant (P < 0.05) reduction in body temperature of 1. 45 +/- 0.33 degreesC after hypoxia (7% inspired O2), whereas systemic and central injections of AVP V1- and AVP V2-receptor blockers caused no change in body temperature. When intravenous injection of AVP blockers was combined with hypoxia, we observed a reduction in body temperature of 1.49 +/- 0.41 degreesC (V1-receptor blocker) and of 1.30 +/- 0.13 degreesC (V2-receptor blocker), similar to that obtained by application of hypoxia only. Similar results were observed when the blockers were injected intracerebroventricularly. The data indicate that endogenous AVP does not mediate hypoxia-induced anapyrexia in rats.