Evidence supporting a role for endogenous vasopressin in fever suppression in the rat

Fever of unknown origin associated with immune checkpoint inhibitors

Since the approval for the treatment of melanoma in 2014, immune checkpoint inhibitors (ICIs) have revolutionized the therapy pattern across various malignancies. Coinciding with their frequent usage, their adverse effects, including fever, cannot be neglected. In the context of cancer diseases and cancer treatments, fever of unknown origin (FUO), which has long posed a challenge for clinicians in terms of diagnosis and management, brings forth new connotation and significance. In this paper review, we present the concept of ICIs-associated FUO, consider activated immune system and elevated cytokines as common mechanisms by which ICIs induce fever and various immune-related adverse events (irAEs), summarize and compare the primary etiologies of ICI-associated FUO, and compare it with conventional types of FUO.

Cytokines in Febrile Diseases

The human body has a perfect thermoregulatory system to meet the needs of normal life activities. The central regulation of body temperature is mainly explained by the theory of "setting point (setpoint, SP)". Fever is a positive but nonspecific response of the body to infections and other pyrogens, which causes immune cells to release cytokines, leading to a brain protein-mediated rise in body temperature. Cytokines can be roughly divided into 2 categories: proinflammatory cytokines and anti-inflammatory cytokines. IL-1, TNF-α, and IL-6 are proinflammatory cytokines, whereas IL-4 and IL-10 are anti-inflammatory cytokines. IL-2 is a cytokine that can both activate and inhibit immunity. IL-8 is a neutrophil chemotactic factor, and IFN is a cytokine that plays a key role in the proper induction and maintenance of innate and acquired immunity. This article reviews the pathophysiological characteristics of fever and the cytokines related to fever (IL-2, 4, 6, 8, 10, IFN, TNF, etc.).

Postnatal expression of V2 vasopressin receptor splice variants in the rat cerebellum

The V(2) vasopressin receptor gene contains an alternative splice site in exon-3, which leads to the generation of two splice variants (V(2a) and V(2b)) first identified in the kidney. The open reading frame of the alternatively spliced V(2b) transcript encodes a truncated receptor, showing the same amino acid sequence as the canonical V(2a) receptor up to the sixth transmembrane segment, but displaying a distinct sequence to the corresponding seventh transmembrane segment and C-terminal domain relative to the V(2a) receptor. Here, we demonstrate the postnatal expression of V(2a) and V(2b) variants in the rat cerebellum. Most importantly, we showed by in situ hybridization and immunocytochemistry that both V(2) splice variants were preferentially expressed in Purkinje cells, from early to late postnatal development. In addition, both variants were transiently expressed in the neuroblastic external granule cells and Bergmann fibers. These results indicate that the cellular distributions of both splice variants are developmentally regulated, and suggest that the transient expression of the V(2) receptor is involved in the mechanisms of cerebellar cytodifferentiation by AVP. Finally, transfected CHO-K1 expressing similar amounts of both V(2) splice variants, as that found in the cerebellum, showed a significant reduction in the surface expression of V(2a) receptors, suggesting that the differential expression of the V(2) splice variants regulates the vasopressin signaling in the cerebellum.

Vasopressin vs. terlipressin in the treatment of cardiovascular failure in sepsis

BACKGROUND

Arginine vasopressin (AVP) and terlipressin (TP) are increasingly used as adjunct vasopressors in the treatment of septic shock. Despite important pharmacological differences between the two drugs (e.g., receptor selectivity, effective half-life) the use of either substance is determined mainly by local availability and institutional inventory. We briefly describe the pathophysiology and pharmacology of septic shock relevant to the treatment with vasopressin analogues. In addition, differences in pharmacokinetics and pharmacodynamics between AVP and TP are discussed.

DISCUSSION

The current literature suggests that neither AVP nor TP should be administered in high doses in patients with septic shock. Furthermore, increasing evidence indicates that early administration of vasopressin analogues may improve outcome as compared to a last-resort treatment. Low-dose infusion of AVP (0.6-2.4 U/h) has been demonstrated to be a safe adjunct in the management of septic shock. The V2 agonistic effects of AVP may exert favorable effects on hepatosplanchnic, renal, pulmonary, and coronary perfusion. However, the higher V1 receptor selectivity of TP may prove more potent in restoring arterial blood pressure and avoiding rebound hypotension, while carrying the risk of sustained global and regional vasoconstriction after bolus injection.

CONCLUSIONS

Evidence from experimental studies and initial clinical reports suggests that continuous low-dose infusion of TP may stabilize hemodynamics in septic shock with reduced side effects. However, randomized, controlled trials are necessary to determine the role of bolus or continuous infusion of TP in the treatment of septic shock before this approach can be recommended for routine clinical use.

Body water balance and body temperature in vasopressin V1b receptor knockout mice

In an attempt to determine whether there is a specific vasopressin receptor (V(1b)) subtype involved in the regulation of body water balance and temperature, vasopressin V(1b) receptor knockout mice were used. Daily drinking behavior and renal excretory function were examined in V(1b)-deficient (V(1b)(-/-)) and control (V(1b)(+/+)) mice under the basal and stress-induced condition. In addition, body temperature and locomotor activity were measured with a biotelemetry system. The baseline daily water intake and urine volume were larger in V(1b)(-/-) mice than in V(1b)(+/+) mice. V(1b)(-/-) mice (V(1b)(-/-)) had significantly higher locomotor activity than wild-type, whereas the body temperature and oxygen consumption were lower in V(1b)(-/-) than in the V(1b)(+/+) mice. Next, the V(1b)(-/-) and V(1b)(+/+) mice were subjected to water deprivation for 48 hr. Under this condition, their body temperature decreased with the time course, which was significantly larger for V(1b)(-/-) than for V(1b)(+/+) mice. Central vasopressin has been reported to elicit drinking behavior and antipyretic action, and the V(1b) receptor has been reported to be located in the kidney. Thus, the findings suggest that the V(1b) receptor may be, at least in part, involved in body water balance and body temperature regulation.

Effects of electrical stimulation of ventral septal area on firing rates of pyrogen-treated thermosensitive neurons in preoptic anterior hypothalamus from rabbits

Although there is considerable evidence supporting that fever evolved as a host defense response, it is important that the rise in body temperature would not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified. Endogenous antipyretics attenuate fever by influencing the thermoregulatory neurons in the preoptic anterior hypothalamus (POAH) and in adjacent septal areas including ventral septal area (VSA). Our previous study showed that intracerebroventricular (I.C.V.) injection of interleukin-1beta (IL-1beta) affected electrophysiological activities of thermosensitive neurons in VSA regions, and electrical stimulation of POAH reversed the effect of IL-1beta. To further investigate the functional electrophysiological connection between POAH and VSA and its mechanisms in thermoregulation, the firing rates of thermosensitive neurons in POAH of forty-seven unit discharge were recorded by using extracellular microelectrode technique in New Zealand white rabbits. Our results show that the firing rates of the warm-sensitive neurons decreased significantly and those of the cold-sensitive neurons increased in POAH when the pyrogen (IL-1beta) was injected I.C.V. The effects of IL-1beta on firing rates in thermosensitive neurons of POAH were reversed by electrical stimulation of VSA. An arginine vasopressin (AVP) V1 antagonist abolished the regulatory effects of VSA on the firing rates in thermosensitive neurons of POAH evoked by IL-1beta. However, an AVP V2 antagonist had no effects. These data indicated that VSA regulates the activities of the thermosensitive neurons of POAH through AVP V1 but not AVP V2 receptor.

Thermoregulatory role of inducible nitric oxide synthase in lipopolysaccharide-induced hypothermia

We have tested the hypothesis that nitric oxide (NO) arising from inducible nitric oxide synthase (iNOS) plays a role in hypothermia during endotoxemia by regulating vasopressin (AVP) release. Wild-type (WT) and iNOS knockout mice (KO) were intraperitoneally injected with either saline or Escherichia coli lipopolysaccharide (LPS) 10.0 mg/kg in a final volume of 0.02 mL. Body temperature was measured continuously by biotelemetry during 24 h after injection. Three hours after LPS administration, we observed a significant drop in body temperature (hypothermic response) in WT mice, which remained until the seventh hour, returning then close to the basal level. In iNOS KO mice, we found a significant fall in body temperature after the fourth hour of LPS administration; however, the hypothermic response persisted until the end of the 24 h of the experiment. The pre-treatment with beta-mercapto-beta,beta-cyclopentamethylenepropionyl(1), O-Et-Tyr2, Val4, Arg8-Vasopressin, an AVP V1 receptor antagonist (10 microg/kg) administered intraperitoneally, abolished the persistent hypothermia induced by LPS in iNOS KO mice, suggesting the regulation of iNOS under the vasopressin release in this experimental model. In conclusion, our data suggest that the iNOS isoform plays a role in LPS-induced hypothermia, apparently through the regulation of AVP release.

Low-dose terlipressin during long-term hyperdynamic porcine endotoxemia: effects on hepatosplanchnic perfusion, oxygen exchange, and metabolism

OBJECTIVE

To investigate whether the vasopressin analog terlipressin might induce hepatosplanchnic ischemia during long-term, hyperdynamic, volume-resuscitated porcine endotoxemia.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Eighteen pigs were divided into two groups receiving either endotoxin alone (control group, n = 10) or endotoxin and terlipressin (n = 8).

INTERVENTIONS

Pigs were anesthetized, mechanically ventilated, and instrumented and received a continuous intravenous infusion of Escherichia coli endotoxin. Animals were resuscitated with hydroxyethyl starch targeted to maintain mean arterial pressure >60 mm Hg. Twelve hours after the start of the endotoxin infusion, terlipressin (5-15 microg.kg.hr titrated to maintain mean arterial pressure at preendotoxin levels) or its vehicle was administered for 12 hrs.

MEASUREMENTS AND MAIN RESULTS

Terlipressin increased mean arterial pressure and systemic vascular resistances, which was affiliated with a decrease in cardiac output and global oxygen consumption. Terlipressin restored the hepatic artery buffer response, which led to an increase in hepatic artery flow, ultimately resulting in well-maintained liver oxygen delivery, oxygen uptake, and all other variables of regional metabolism and organ function. Terlipressin markedly attenuated the hepatosplanchnic venous acidosis but was associated with pronounced hyperlactatemia.

CONCLUSIONS

During long-term hyperdynamic porcine endotoxemia, the well-known vasoconstrictor properties of terlipressin blunted the progressive decrease in mean arterial pressure without any detrimental effect on hepatosplanchnic perfusion, oxygen exchange, and metabolism. The marked terlipressin-induced hyperlactatemia did not originate from the hepatosplanchnic organs but from extrasplanchnic tissues, possibly muscle and skin.

Hodological characterization of the septum in anuran amphibians: II. Efferent connections

The efferent connections of the septum of the gray treefrog Hyla versicolor were studied by combining anterograde and retrograde tracing with biotin ethylendiamine (Neurobiotin). The lateral septal complex projects mainly to the medial pallium, limbic regions (e.g., amygdala and nucleus accumbens), and hypothalamic areas but also to sensory nuclei in the diencephalon and midbrain. The central septal complex strongly innervates the medial pallium, limbic, and hypothalamic areas but also specific sensory (including olfactory) regions. The medial septal complex sends major projections to all olfactory nuclei and a weaker projection to the hypothalamus. Our results indicate that all septal nuclei may modify the animal's internal state via efferents to limbic and hypothalamic areas. Via projections to the medial pallium, lateral and central septal complexes may be involved in learning processes as well. Because of their connections to specific sensory areas, all septal areas are in a position to influence sensory processing. Furthermore, our data suggest that both the postolfactory eminence and the bed nucleus of the pallial commissure are not part of the septal complex, rather, the postolfactory eminence seems to be comparable to the mammalian primary olfactory cortex, whereas the bed nucleus may be analogous to the mammalian subfornical organ.

Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 microg/1 microl) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When L-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with beta-mercapto-beta,beta-cyclopentamethylenepropionyl1, O-Et-Tyr2, Val4, Arg8-vasopressin, an AVP V1 receptor blocker (10 microg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.

Systemic salt loading decreases body temperature and increases heat-escape/cold-seeking behaviour via the central AT1 and V1 receptors in rats

Salt loading decreases body core temperature (T(core)) at neutral ambient temperature (26 degrees C) and increases heat-escape/cold-seeking behaviour in desalivated rats. In this study, we tested the hypothesis that brain angiotensin II (AII) and arginine vasopressin (AVP) are associated with these responses. Surgically desalivated rats (n = 28) were administered an injection (S.C., 10 ml kg(-1)) of either normal saline (154 mM, NS) or hypertonic saline (2500 mM, HS) following an intracerebroventricular injection (10 microl kg(-1)) of an AII AT(1)-receptor antagonist (candesartan, 5 microg microl(-1)), an AVP V(1)-receptor antagonist ((beta-mercapto-beta, beta-cyclopenta-methylene propionyl(1), O-Me-Tyr(2), Arg(8))-vasopressin, 0.5 microg microl(-1)), or normal saline (154 mM). Each rat was placed in a behaviour box, first at 26 degrees C for 1 h to allow the measurement of baseline T(core) and movement. The ambient temperature was then elevated to 40 degrees C for the next 2 h, during which time the rat was able to trigger a 0 degrees C air reward for 30 s by moving into a specific area of the box (operant behaviour). The S.C. HS significantly decreased baseline T(core) at 26 degrees C (36.5 +/- 0.1 degrees C) and increased counts of operant behaviour at 40 degrees C (57 +/- 3) compared with results obtained following S.C. NS injection (37.4 +/- 0.1 degrees C and 42 +/- 1, respectively). These responses to s.c. HS were inhibited by the intracerebroventricular injection of AT(1) (37.3 +/- 0.1 degrees C and 43 +/- 2, respectively; P < 0.05) and V(1) antagonists (37.2 +/- 0.2 degrees C and 42 +/- 2, respectively; P < 0.05), although administration of both antagonists with S.C. NS had no effect. These results suggest that brain AII and AVP are involved in the decrease in T(core) observed at neutral ambient temperature and the increase in heat-escape/cold-seeking behaviour in response to osmotic stimulation, via the central AT(1) and V(1) receptors, respectively

Peri-OVLT E-series prostaglandins and core temperature do not increase after intravenous IL-1beta in pregnant rats

Rats have an attenuated febrile response to endogenous pyrogen near the term of pregnancy. Given the fundamental role of E-series prostaglandins (PGEs) in mediating the febrile response to blood-borne endogenous pyrogen, the present experiments were carried out to determine whether PGEs increase in the area surrounding the organum vasculosum laminae terminalis (peri-OVLT) of near-term pregnant (P) rats as in nonpregnant (NP) rats after intravenous (iv) administration of recombinant rat interleukin-1beta (rrIL-1beta). Core temperature was measured by telemetry and peri-OVLT interstitial fluid was sampled in 12 NP and 12 P chronically instrumented, Sprague-Dawley rats by microdialysis for determination of total PGEs by radioimmunoassay. Basal core temperatures were higher in NP compared with P rats (NP 37.9 degrees C +/- 0.5, P 36.9 degrees C +/- 0.4; P < 0.05), but basal peri-OVLT PGEs were similar in both groups (NP 260 +/- 153 pg/ml, P 278 +/- 177 pg/ml; P =not significant). Intravenous administration of rrIL-1beta to NP rats produced a significant increase in core temperature with a latency, magnitude, and duration of 10 min, 0.87 degrees C, and at least 170 min, respectively; peri-OVLT PGEs were increased significantly by 30 min and averaged 270% above basal levels throughout the experiment. In P rats, however, neither core temperature nor peri-OVLT PGEs increased significantly after iv administration of rrIL-1beta. Intravenous administration of vehicle did not significantly alter core temperature or peri-OVLT PGEs in either group of rats. Thus peri-OVLT PGEs do not increase in P rats as they do in NP rats after iv administration of rrIL-1beta. The mechanism of this interesting component of the maternal adaptation to pregnancy, which likely plays a major role in mediating the attenuated febrile response to endogenous pyrogen near the term of pregnancy, warrants further investigation.

Arginine vasopressin, fever and temperature regulation

While central administration of arginine vasopressin (VP) to the non-febrile rat at high doses can cause hypothermia, there is little evidence for a role for endogenous VP in normal thermoregulation. In contrast, VP arising from cell bodies in the bed nucleus of the stria terminalis and innervating the ventral septal areas and possibly the amygdala appears to be an endogenous antipyretic, i.e. a substance capable of reducing fever. As the synthesis of VP in bed nucleus neurons is dependent upon circulating androgens, female rats have much less VP in these cells and their projections than do male rats. In keeping with this, females may make use of VP to a lesser extent than do males to bring about antipyresis. The phenomenon whereby the VP receptor can become sensitized by previous exposure to VP may be responsible for some states of endogenous antipyresis, in which fevers are suppressed through overactivity of the vasopressinergic system. States of endogenous antipyresis can be revealed around the time of parturition in both the neonate and the mother.

Co-localization of interleukin-1 receptor type I and interleukin-1 receptor antagonist with vasopressin in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus

Interleukin-1 receptor type I and interleukin-1 receptor antagonist were found in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus by immunohistochemical detection. Double-labelling experiments revealed that both proteins occurred in vasopressin-containing neurons. A similar distribution pattern was observed in a group of vasopressin-positive accessory magnocellular neurons. Axons emanating from the interleukin-1 receptor type I- and interleukin-1 receptor antagonist-immunoreactive neuronal cell bodies could be seen within the hypothalamic nuclei, and varicosities expressing interleukin-1 receptor antagonist immunoreactivity were observed in the internal zone of the median eminence, as well as in the hypothalamo-pituitary projection. The co-localization of interleukin-1 receptor type I with vasopressin is in agreement with findings that interleukin-1 has a stimulatory effect on vasopressin synthesis and release. The hypothalamic neurons may serve as a source of interleukin-1 receptor antagonist to balance the effects of interleukin-1.

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.

Arginine vasopressin does not mediate the attenuated febrile response to intravenous IL-1beta in pregnant rats

Rats have an attenuated febrile response to intravenous endogenous pyrogen [e.g., interleukin-1beta (IL-1beta)] near the term of pregnancy. The present experiments were carried out on 25 nonpregnant and 32 pregnant rats to test the hypothesis that arginine vasopressin functioning as an endogenous antipyretic substance in the central nervous system mediates this attenuated febrile response. An intravenous injection of recombinant rat IL-1beta (rrIL-1beta) after intracerebroventricular vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which was greater in the nonpregnant rats. In nonpregnant rats, intravenous rrIL-1beta after intracerebroventricular vasopressin V1-receptor antagonist accentuated the core temperature response compared with that observed with intravenous rrIL-1beta after intracerebroventricular vehicle. In pregnant animals, however, intravenous rrIL-1beta after intracerebroventricular vasopressin V1-receptor antagonist produced a decrease in core temperature rather than an increase in core temperature, which was observed with intravenous rrIL-1beta after intracerebroventricular vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin as an endogenous antipyretic substance in the central nervous system attenuates the febrile response to intravenous rrIL-1beta near the term of pregnancy in rats.

Role of nitric oxide in systemic vasopressin-induced hypothermia

It has been reported that arginine vasopressin (AVP) plays a thermoregulatory action, but very little is known about the mechanisms involved. In the present study, we tested the hypothesis that nitric oxide (NO) plays a role in systemic AVP-induced hypothermia. Rectal temperature was measured before and after AVP, AVP blocker, or NG-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor) injection. Control animals received saline injections of the same volume. The basal body temperature (Tb) measured in control animals was 36.53 +/- 0.08 degreesC. We observed a significant (P < 0.05) reduction in Tb to 35.44 +/- 0.19 degreesC after intravenous injection of AVP (2 micrograms/kg) and to 35.74 +/- 0. 10 degreesC after intravenous injection of L-NAME (30 mg/kg). The systemic injection of the AVP blocker [beta-mercapto-beta, beta-cyclopentamethylenepropionyl1,O-Et-Tyr2,Val4,Arg8]vasopressin (10 micrograms/kg) caused a significant increase in Tb to 37.33 +/- 0.23 degreesC, indicating that AVP plays a tonic role by reducing Tb. When the treatments with AVP and L-NAME were combined, systemically injected L-NAME blunted AVP-induced hypothermia. To assess the role of central thermoregulatory mechanisms, a smaller dose of L-NAME (1 mg/kg) was injected into the third cerebral ventricle. Intracerebroventricular injection of L-NAME caused an increase in Tb, but when intracerebroventricular L-NAME was combined with systemic AVP injection (2 micrograms/kg), no change in Tb was observed. The data indicate that central NO plays a major role mediating systemic AVP-induced hypothermia.

Vasopressin-induced antipyresis. Sex- and experience-dependent febrile responses

There is now good evidence that vasopressin (AVP) acts, in the male rat, as a neurotransmitter in the ventral septal area to reduce fever. In light of the well known sexual dimorphism in the AVP innervation of the brain, we asked if female rats would (a) display fevers different from those seen in male rats, (b) respond to AVP with antipyresis, (c) display evidence of endogenous AVP-induced antipyresis during fever, and (d) display altered fevers and AVP involvement as a function of hormonal status. Our experiments indicate that female rats display larger fevers to intracranial prostaglandin E2 (PGE2) but not to systemic lipopolysaccharide or interleukin-1 beta than do male rats. The larger fevers may be due, in part, to a lack of AVP-induced antipyresis, as an AVP antagonist elevates PGE2 fever in male but not in female rats and dialysates of the ventral septal area show increased AVP levels only in male rats during defervescence. Nonetheless, females respond to exogenous AVP with antipyresis. Throughout late pregnancy, parturition, and lactation, PGE2 fevers are reduced, but this appears to be due to a general suppression of autonomic output not involving enhanced AVP antipyresis. Fevers due to lipopolysaccharide and interleukin-1 beta are also suppressed at this time, and in some animals, fevers are dramatically suppressed at about the time of parturition. Our results indicate that female rats may utilize different strategies for antipyresis than do male rats and that hormonal status may influence both peripherally generated and centrally activated fevers.

AVP mediates the attenuated febrile response to administration of PGE1 in rats near term of pregnancy

Rats have an attenuated febrile response to intracerebroventricular injection of PGE1 near the term of pregnancy, the mechanism of which is unknown. The present experiments were carried out to test the hypothesis that arginine vasopressin (AVP), functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated febrile response. The febrile response to intracerebroventricular injection of 0.2 microg PGE1 was determined in pregnant and nonpregnant rats after an intracerebroventricular injection of either vehicle or a vasopressin V1-receptor antagonist. After intracerebroventricular administration of vehicle, intracerebroventricular administration of 0.2 microg PGE1 produced significant increases in core temperature in both nonpregnant and pregnant animals. The increase in core temperature, however, was attenuated both in magnitude and duration in pregnant compared with nonpregnant animals. After intracerebroventricular administration of a vasopressin V1-receptor antagonist, intracerebroventricular administration of 0.2 microg PGE1 produced significant increases in core temperature that were similar in nonpregnant and pregnant animals. Our data support the hypothesis that a pregnancy-related activation of AVP as an endogenous antipyretic substance in the central nervous system attenuates the febrile response to intracerebroventricular administration of PGE1 near term of pregnancy in rats.

C3H/HeJ mice are refractory to lipopolysaccharide in the brain

C3H/HeJ mice are refractory to lipolysaccharide (LPS) in the periphery, primarily because their macrophages do not respond to LPS and produce pro-inflammatory cytokines such as interleukin-1 (IL-1). To determine if they are also refractory to LPS in the brain, behavior of C3H/HeJ mice was compared to LPS-sensitive C3H/HeOuJ mice following intracerebroventricular (I.C.V.) injection of LPS. Whereas ICV injection of LPS (3-1000 ng/mouse) depressed social behavior, food motivation, object investigation and body weight in C3H/HeOuJ mice, C3H/HeJ mice were entirely refractory to LPS in the brain. To determine if the refractoriness of C3H/HeJ mice could result from an inability to synthesize IL-1, recombinant murine IL-1 was injected I.C.V. in both mouse strains. Central administration of IL-1 (1 or 2 ng/mouse) depressed social behavior and body weight similarly in both endotoxin-sensitive C3H/HeOuJ mice and endotoxin-resistant C3H/HeJ mice. That C3H/HeJ mice were refractory to the behavioral effects of central LPS, but not IL-1, suggests that microglia (and other cells in the brain) in C3H/HeJ mice have in common with peripheral macrophages, an inability to respond to LPS and produce cytokines. These data suggest a genetic basis for sickness behavior and demonstrate the utility of preventing central cytokine production in manipulating LPS-induced sickness behavior.

Arginine vasopressin release by acetylcholine or norepinephrine: region-specific and cytokine-specific regulation

Interferon-alpha and transforming growth factor-beta 1 have been detected in the brain, suggesting their possible regulatory functions. In the present study, we evaluated the effects of these cytokines on the in vitro release of arginine vasopressin, previously reported to be sensitive to neurotransmitters such as acetylcholine, norepinephrine, and corticotropin releasing hormone as well as to cytokines interleukin-1 and interleukin-2. Interferon-alpha was found to enhance arginine vasopressin release from both hypothalamus and amygdala, as was dibutyryl cyclic GMP. Blockade of nitric oxide synthase antagonized the interferon-alpha induced arginine vasopressin release from the amygdala but not from the hypothalamus. Transforming growth factor-beta 1 had no effect on basal release of arginine vasopressin, nor on the arginine vasopressin-release induced by interferon-alpha, interleukin-2 or norepinephrine, but selectively blocked the acetylcholine-induced release in both hypothalamus and amygdala. When the release of arginine vasopressin induced by interferon-alpha, interleukin-2, acetylcholine and norepinephrine was probed with inhibitors of guanylate cyclase, the interactions exhibited regional selectivity: neither the interleukin-2-induced arginine vasopressin release from hypothalamus, nor the norepinephrine-induced release of arginine vasopressin from either amygdala or hypothalamus was affected by guanylate cyclase inhibitors, but all other arginine vasopressin releasers were blocked. Taken with previous reports that interferon-alpha will enhance hypothalamic corticotropin releasing hormone release, our results suggest that arginine vasopressin release enhanced by interferon-alpha may also contribute to the activation of the hypothalamic-pituitary axis, while the ability of transforming growth factor-beta 1 to diminish the arginine vasopressin released by acetylcholine could mediate some of this cytokine's central effects. The extension of these neurotransmitter-cytokine interactions to the amygdala may provide an additional basis for interactions between neuronal and immune systems.

Vasopressin and galanin mRNAs coexist in the nucleus of the horizontal diagonal band: a novel site of vasopressin gene expression

Vasopressin (VP) neurons have been identified in several brain regions where VP has been hypothesized to act as a neurotransmitter or neuromodulator. In many sites, VP is colocalized with the neuropeptide galanin (GAL). Here, using single in situ hybridization histochemistry, we have identified a novel group of neurons within the nucleus of the horizontal diagonal band of Broca (HDB) that express the VP gene and have assessed the distribution of these cells in adult male and female rats (90 days old, n = 7/group). VP mRNA-expressing neurons were scattered throughout the rostrocaudal extent of the HDB, and the number of VP neurons detected unilaterally ranged from 1 to 17 cells per 20 microns section. Using double in situ hybridization histochemistry on alternate sections, we have assessed the number of cells expressing VP and/or GAL mRNA in the diagonal band and have determined the extent of their colocalization. Approximately 50% of all VP-expressing neurons in the HDB coexpressed GAL mRNA, and 33% of GAL-expressing neurons in this region coexpressed VP mRNA. No sex differences were detected in the number of neurons expressing either VP or GAL mRNA or in the incidence of coexpression of VP and GAL mRNAs in this region. VP neurons in the HDB exhibited a low level of expression, and cellular VP mRNA content did not differ between male and female rats. However, sex differences were present in the bed nucleus of the stria terminalis (BNST) of these same rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of the physiological responses to indomethacin by endotoxin tolerance in the rat: a possible role for central vasopressin

1. Previous studies suggest that arginine vasopressin (AVP) is released into the ventral septal area (VSA) of the rat brain during the antipyresis induced by the cyclo-oxygenase inhibitor indomethacin. In addition, there is evidence for increased AVP transmission in the VSA of animals having a reduced pyretic response following three intravenous injections of bacterial endotoxin (LPS) (endotoxin tolerant). Since ventral septal AVP receptors can also become 'sensitized' following exposure to AVP, we questioned whether the antipyretic action of indomethacin would increase, via an action involving central AVP, if this drug were administered into LPS-tolerant rats. 2. Intraperitoneal indomethacin (7.5 mg kg-1) was effectively antipyretic when administered 2 h after an intravenous challenge with LPS (50 micrograms kg-1) into conscious unrestrained rats. This dose of indomethacin had no effect on the core temperature of non-febrile rats given intravenous 0.9% pyrogen-free saline. 3. Three intravenous injections of LPS over a period of 3 days resulted in rats that were tolerant to the pyrogenic effects of LPS. When indomethacin was administered 2 h following the third LPS injection, a dose-dependent hypothermia was observed. This effect was age dependent, as profound hypothermia was seen in 8 week but not 20 week old rats. 4. A mortality rate of 41% (P = 0.02) was observed within 24 h of indomethacin treatment in 8 week old tolerant rats compared with 0% in 8 week old non-tolerant and 20 week old tolerant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Does endogenous peripheral arginine vasopressin have a role in the febrile responses of conscious rabbits?

1. The actions of peripheral arginine vasopressin (AVP) on the febrile responses of conscious rabbits induced by peripherally administered polyinosinic:polycytidylic acid (poly(I).poly(C)) have been studied using an AVP V1 receptor antagonist ([deamino-Pen1, O-Me-Tyr2, Arg8]-vasopressin). 2. Temperature responses were monitored continuously using rectal thermistor probes. Test substances were administered intravenously (i.v.). Blood samples were taken at timed intervals from a marginal ear vein and plasma PGE2 and PGF2 alpha levels determined by radioimmunoassay. 3. Poly(I).poly(C) (2.5 micrograms/kg) stimulated a reproducible biphasic rise in body temperature with a lag phase of 45-60 min and peaks at 90 and 225 min. The febrile response was accompanied by a 5-fold rise in circulating immunoreactive (ir) PGE2, which peaked after 90 min and remained elevated up to 300 min. Poly(I).poly(C) also stimulated a 2.5-fold rise in circulating irPGF2 alpha, which peaked after 150 min and was followed by a return to basal levels after 300 min. 4. The overall magnitude of the febrile response to poly(I).poly(C) (2.5 micrograms/kg, i.v.) was significantly antagonized by the AVP V1 receptor antagonist (250 micrograms/kg, i.v.) administered 5 min prior to the pyrogen. 5. The irPGE2 response to poly(I).poly(C) (2.5 micrograms/kg, i.v.) was significantly antagonized by the AVP V1 receptor antagonist (250 micrograms/kg, i.v.) administered 5 min prior to the pyrogen. The irPGF2 alpha response was only reduced at the peak 150 min time point measurement. 6. In conclusion, these results show a modulatory role for a peripherally administered AVP V1 antagonist in the febrile responses to poly(I).poly(C), suggesting a possible propyretic role for endogenous peripheral AVP. This modulatory role appears to be mediated via actions on prostaglandin E2.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Central effects of interleukin-1 on blood pressure, thermogenesis, and the release of vasopressin, ACTH, and atrial natriuretic peptide

To assess the central role of interleukin 1-beta (IL-1 beta) in the release of ACTH, vasopressin (AVP) and atrial natriuretic peptide (ANP) and in the regulation of blood pressure and thermogenesis, 3 ng (0.173 pM) x 100-1 x BW-1 (LIL), 30 ng (1.73 pM) x 100g-1 x BW-1 (MIL), and 150 ng (8.63 pM) x 100g-1 x BW-1 (HIL) of human IL-1 beta dissolved in sterile saline were injected intracerebroventricularly to conscious rats. In the control rats, saline alone (5 microliters) was administered. In three other groups, rats were pretreated with indomethacin, a cyclooxygenase inhibitor, given i.v. (1 mg x 100g-1 x BW-1); medium and high doses of IL-1 beta or its vehicle were given. In the LIL group, IL-1 beta increased blood pressure, body temperature and plasma AVP and ANP without any changes in heart rate (HR) and plasma ACTH. In the MIL group, plasma ACTH was increased, and changes in the other parameters were similar to those in the LIL group. In the HIL group, however, the pressor and thermogenetic responses were attenuated; plasma AVP, ACTH, and ANP were increased; and HR was unchanged. In the control (CON) group, none of these parameters was changed throughout the studies. Indomethacin abolished the AVP and ACTH responses to IL-1 beta, but potentiated the pressor and hypothermic responses and increased plasma ANP. These data suggest that the actions of IL-1 beta on AVP and ACTH release and thermogenesis, but not on blood pressure and the release of ANP, are modulated by the stimulated central production of prostaglandins.

Extra-hypothalamic vasopressin neurons coexpress galanin messenger RNA as shown by double in situ hybridization histochemistry

Vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BNST) and medial amygdala (AMe) exhibit sexual dimorphism and steroid dependency. VP neurons in the supraoptic nucleus and paraventricular nucleus have been shown to coexpress other transmitters including galanin (GAL). However, little is known about what other neurotransmitters may be colocalized with VP in the BNST and AMe. Here, we have used radio-labeled and digoxigenin-labeled cRNA probes to perform double in situ hybridization histochemistry for VP and GAL in the BNST and AMe of intact, adult male rats. We provide evidence that in the basal state, the majority of VP-synthesizing cells in the BNST and AMe of the adult male rat also express galanin mRNA. Likewise, the majority of GAL-expressing neurons in these regions also contain VP mRNA. These findings give further evidence for the similarity of the BNST and AMe and provide a rationale for studies investigating the role of GAL in functions involving extrahypothalamic VP pathways.

Chronic intracerebral infusions of vasopressin and vasopressin antagonist modulate behavioral effects of interleukin-1 in rat

To assess the role of sex dependent brain vasopressinergic transmission in the modulation of the neural effects of interleukin-1, castrated male rats that are deficient in vasopressin were implanted intracerebroventricularly with an Accurel collodion mini device containing 10 micrograms AVP whereas intact male rats were implanted with a similar device containing 50 micrograms of dPTyr(Me)AVP, a specific antagonist of the vasopressor-like receptors of vasopressin. Control rats in each sex group were implanted with an Accurel device containing distilled water. Acute intracerebroventricular injection of 1.25-2.50 ng recombinant human interleukin-1 beta decreased in a dose and time-dependent manner social investigation of a juvenile conspecific. This effect was more intense in intact rats chronically infused with dPTyr(Me)AVP and less intense in castrates infused with AVP. These results confirm the modulatory role of sex-dependent vasopressinergic neurotransmission on the neural effects of interleukin-1.

Vasopressin perfusion within the medial amygdaloid nucleus attenuates prostaglandin fever in the urethane-anaesthetized rat

The antipyretic effect of arginine vasopressin (AVP) introduced into the ventral septal area (VSA) by push-pull perfusion was investigated in the urethane-anaesthetized rat. In addition, experiments were carried out to determine whether AVP could suppress fever when similarly perfused within the medial amygdaloid nucleus (meA). During push-pull perfusion of artificial cerebrospinal fluid within the VSA or meA, PGE1 injected intracerebroventricularly evoked fevers with respective magnitudes of 1.3 +/- 0.2 degrees C and 1.4 +/- 0.3 degrees C above baseline. Perfusion of AVP (6.5 micrograms/ml) within the VSA had significantly reduced the magnitude of PGE1 fever to 0.3 +/- 0.3 degrees C above baseline, while having no significant effect on afebrile colonic temperature. Perfusion of AVP (6.5 micrograms/ml) within the meA had significantly attenuated the magnitude of PGE1 fever to 0.7 +/- 0.2 degrees C above baseline, while having no significant effect on afebrile colonic temperature. These results support further the utility of the urethane-anaesthetized rat model for future investigations of the central control of fever and antipyresis. In addition, these data are consistent with the hypothesis that AVP may act within the meA as an endogenous antipyretic.

Androgen-dependent vasopressinergic neurotransmission attenuates interleukin-1-induced sickness behavior

Castrated male rats were found to be more sensitive than intact male rats to the depressing effects of recombinant human interleukin-1 beta (Il-1) on social exploration. This was the case whether Il-1 was injected acutely (1-5 micrograms/rat, i.p.) or continuously, via an implanted osmotic mini-pump (2 micrograms Il-1 per day). In this latter case, tolerance developed more rapidly to the behavioral effects of Il-1 than to its effects on body weight. Since there is evidence that extrahypothalamic arginine vasopressin (AVP) acts as an endogenous antipyretic in the brain and the local concentration of AVP is dependent on circulating androgens, we tested the hypothesis that the enhanced sensitivity of male rats to the behavioral effects of Il-1 was caused by a reduced brain concentration of vasopressin. Central injection of AVP (2.5 ng, i.c.v.) attenuated the behavioral effects of Il-1 (5 ng, i.c.v.) and this effect was more marked in castrated than in intact male rats. Conversely, central injection of an antagonist of the vasopressor receptors of AVP, dPTyr(Me)AVP (15 ng, i.c.v.) potentiated the behavioral effects of Il-1 (1 ng, i.c.v.) in intact but not in castrated male rats. These results are consistent with the possibility that androgen-dependent vasopressinergic neurons oppose the neural effects of Il-1.

Vasopressin in the septal area of the golden hamster controls scent marking and grooming

Microinjection of arginine vasopressin into the lateral septum and bed nucleus of the stria terminalis of male hamsters stimulates intense flank marking and flank gland grooming, while microinjections of vasopressin in sites immediately adjacent to these areas or in the lateral ventricle are ineffective. Microinjections of oxytocin, angiotensin II and the behaviorally active C-terminal fragment of vasopressin, metabolite neuropeptide, by comparison, do not stimulate flank marking. Effective sites for vasopressin injection are clearly superimposable upon autoradiographically defined sites of high V1-receptor density. Furthermore, vasopressin-sensitive neurons in the lateral septum and bed nucleus of the stria terminalis are necessary for the expression of naturally elicited flank marking since the microinjection of a V1-receptor antagonist into these sites was able to temporarily block flank marking triggered by odors from conspecifics.

Influence of interleukin-1 beta on the secretion of oxytocin and vasopressin from the isolated rat neurohypophysis

The effect of the cytokine interleukin-1 beta on the secretion of oxytocin and vasopressin from electrically stimulated rat neurohypophysis was examined in vitro. The release of oxytocin and vasopressin was concentration-dependently increased by interleukin-1 beta in the concentration range from 4.4 pM to 440 pM. The effect of interleukin-1 beta on oxytocin secretion was less intense as compared to vasopressin. After 440 pM interleukin-1 beta the electrically evoked release of oxytocin was increased about 22% and had not reached its maximum. The vasopressin response was maximal after 44 pM interleukin-1 beta, the response being increased 43% compared to control. No trace of interleukin-1 beta was found in the posterior pituitary (less than 350 pmol/lobe, radioimmunoassay). The results indicate that interleukin-1 beta might be involved the regulation of oxytocin and vasopressin at the pituitary level.

The effectiveness of arginine vasopressin and sodium salicylate as antipyretics in the Brattleboro rat

The infusion of either 30 micrograms/microliters (approx. 100 micrograms/kg/h) of sodium salicylate or 10 ng/microliters (10(-5) M) arginine vasopressin within the ventral septal area of the Brattleboro rat brain reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. Conversely, the infusion of a related peptide, oxytocin (10 ng/microliters (10(-5) M), or 33 ng/kg/h) failed to alter the rise in core temperature following the PGE1 injection. These results suggest that the vasopressin receptors reported to be present in the Brattleboro rat may respond normally to exogenously administered vasopressin, thus allowing for the antipyretic action. Moreover, the antipyretic effects of sodium salicylate suggest that aspirin-like drugs may induce the release of alpha-melanocyte-stimulating hormone which, in turn, attenuates the PGE1-evoked fever. Given recent evidence, however, which suggests that the Brattleboro rat may contain vasopressin both peripherally and within the brain, the antipyretic action of sodium salicylate may be alternatively explained through the endogenous release of vasopressin.

Interleukin-1 beta stimulates the release of vasopressin from rat neurohypophysis

The release of vasopressin from the isolated superfused rat neurohypophysis was measured. The electrically evoked release of vasopressin after phasic submaximal stimulation was increased on exposure to the cytokine, interleukin-1 beta (44 pM). The release returned to its control level when the peptide was withdrawn. The results indicates a permissive role of interleukin-1 beta in the release of vasopressin.

Indomethacin-induced antipyresis in the rat: role of vasopressin receptors

Infusion of 15 micrograms/microliters (approximately 120 micrograms/kg/h) of indomethacin within the ventral septal area of the rat brain significantly reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. A bolus injection of a V1 receptor antagonist, d(CH2)5Try(Me)AVP, (200, 2000, or 20,000 pmol) within the ventral septal area had no effect of body temperature alone but did suppress the PGE1-induced fever. Similar bolus injections of the V1 receptor antagonist within the ventral septal area failed to alter the antipyretic action of indomethacin on the hyperthermia resulting from centrally administered PGE1. Central injections of a V2 receptor antagonist failed to alter either the PGE1-induced fever or the indomethacin-evoked antipyresis. The results suggest that the V1 receptor antagonist may exert non-specific neurodepressant effects which may interfere with the expression or production of PGE1 hyperthermia and may further mask any contribution of arginine vasopressin to the antipyretic effects of indomethacin.

Physiological antagonism between prostaglandin E2 and neuropeptide Y on thermoregulation in the dog

These experiments were undertaken to determine whether neuropeptide Y (NPY) could suppress a prostaglandin hyperthermia in conscious dogs. Prostaglandin E2 (PGE2) (5 micrograms), injected into the lateral cerebral ventricle (ILV), evoked a hyperthermia of approximately 1 degrees C. Addition of ILV NPY (5 micrograms) significantly attenuated the PGE2-induced hyperthermia, whereas pancreatic polypeptide (PP), another member of the PP family peptide, did not. These results provide evidence for a role of NPY on thermoregulation in the dog.

Single-unit activity in the bed nucleus of the stria terminalis during fever

Arginine vasopressin, released from nerve terminals in the septal region, probably exerts endogenous antipyretic activity. A major source of vasopressin to this area is the bed nucleus of the stria terminalis (BST). In order to characterize electrophysiologically the BST-septal pathway and its potential role in the control of fever, single-unit, extracellular recordings were made from neurons in the BST of anesthetized rats. Afferent and efferent connections were identified by electrical stimulation of the medial amygdaloid nucleus and the ventral septal area (VSA). BST neurons received both inhibitory and excitatory synaptic input from the amygdala and VSA. Efferents to the VSA were identified by stimulus-evoked antidromic spike invasion. Some BST neurons were responsive to peripheral skin temperature (thermoresponsive). The activity of putative vasopressin neurons was studied during prostaglandin E1-induced fever. Although a majority of BST units was unaffected by fever, a proportion of the cells examined increased their firing rates in accordance with reported release of vasopressin in the VSA during fever.