Absence of endotoxin-fever but not hyperthermia in Brattleboro rats

Hypoxia-induced anapyrexia: implications and putative mediators

Hypoxia elicits an array of compensatory responses in animals ranging from protozoa to mammals. Central among these responses is anapyrexia, the regulated decrease of body temperature. The importance of anapyrexia lies in the fact that it reduces oxygen consumption, increases the affinity of hemoglobin for oxygen, and blunts the energetically costly responses to hypoxia. The mechanisms of anapyrexia are of intense interest to physiologists. Several substances, among them lactate, adenosine, opioids, and nitric oxide, have been suggested as putative mediators of anapyrexia, and most appear to act in the central nervous system. Moreover, there is evidence that the drop in body temperature in response to hypoxia, unlike the ventilatory response to hypoxia, does not depend on the activation of peripheral chemoreceptors. The current knowledge of the mechanisms of hypoxia-induced anapyrexia are reviewed.

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.

"Biphasic" fevers often consist of more than two phases

This paper disproves the common belief that all doses of lipopolysaccharide (LPS) that are commonly referred to as biphasic fever inducing (>/=2 microg/kg) cause truly biphasic responses. A catheter was implanted into the right jugular vein of several strains of adult male rats, and the animals were habituated to the experimental conditions. At an ambient temperature of 30.0 degrees C, loosely restrained animals were injected with a 10 microg/kg dose of LPS (various preparations), and their colonic (Tc) and tail skin temperatures were monitored (from >/=1 h before to >/=7 h after the injection). The results are presented as time graphs and phase-plane plots; in the latter case the rate of change of Tc is plotted against Tc. In experiment 1 the intravenous injection of LPS (from Escherichia coli 0111:B4, phenol extract) into the rats (Bkl:Wistar) induced a triphasic febrile response, as is obvious from time graphs of Tc (3 peaks), time graphs of effector activity (3 waves of tail skin vasoconstriction), and phase-plane plots (3 complete loops); the injection of saline (control) induced no Tc changes. We analyzed whether the triphasic pattern was due to some peculiarities of the experimental design, i.e., the pyrogen preparation used (experiment 2) or the rat strain tested (experiment 3) or whether this pattern reflects a more general law. In experiment 2 we used the same (phenol) preparation of different LPS (from Shigella flexneri 1A and Salmonella typhosa) and a different preparation (TCA extract) of the same LPS (E. coli). Regardless of the LPS used, rats of the Bkl:Wistar strain responded to the 10 microg/kg dose with the triphasic fever. In experiment 3, rats of other strains [Bkl:Sprague-Dawley and Sim:(LE)fBR(Black-hooded)] were tested. Again, all animals responded to the 10 microg/kg dose of E. coli LPS (phenol extract) with the triphasic fever. Because all fevers caused by four different LPS preparations in three rat strains were triphasic, the triphasic pattern is likely to constitute an intrinsic characteristic of the febrile response.

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.

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.

E-series prostaglandins and arginine vasopressin in the modulation of male sexual behavior

Studies carried out recently in the author's laboratory have suggested that fever accompanies copulation in the male rat. Given the action of prostaglandin-E (PGE) in the genesis of fever and given the integrative role of the medial preoptic area (MPOA) in the expression of both fever and male sexual behavior, two hypotheses were advanced concerning male copulation. The first concerns PGE in facilitating transmission in MPOA pathways mediating mounting, intromission and ejaculation. The second concerns arginine vasopressin, a presumed "natural antagonist" of PGE, in inhibiting such transmission and eventually making the male refractory to the receptive female. Several experiments were suggested for testing each hypothesis.

Antipyretic doses of centrally administered vasopressin reach physiologically meaningful concentrations in the brain of the rat as evaluated by microdialysis

It was important to determine whether vasopressin (AVP) injected intracerebroventricularly (i.c.v.) in the rat reached the site of action within the ventral septal area (VSA) in sufficient concentrations to account for its physiological effects. Microdialysis was used to evaluate this hypothesis. The exchange rate across the dialysis tubing was determined in vitro to be 0.40%. After placement of the microdialysis cannula in the VSA of the rat the recovery of i.c.v. injected labelled or cold AVP was 0.23 and 0.20%, respectively. Maximum concentrations of AVP in the extracellular fluid of the VSA was determined to be 10.7 nM after 10 ng i.c.v. and hence extrapolated to be 1.07 nM after 1 ng i.c.v. or 2.65 nM after 2.5 ng i.c.v. between which lies the threshold dose of AVP for its antipyretic effects. This can be compared with a reported Kd for these receptors of 1.06 nM as determined by receptor binding assay.

Criteria for establishing a physiological role for brain peptides. A case in point: the role of vasopressin in thermoregulation during fever and antipyresis

This paper has attempted to present and discuss the criteria necessary for the evaluation of a specific physiological role for a peptide in the CNS. These criteria are based on many experimental approaches to the problem and conclusions must be supported by the weight of the evidence. These criteria were illustrated by examining the hypothesis that AVP is an antipyretic neurotransmitter involved in regulating febrile increases in Tb by release and action in the VSA of the brain. The weight of the evidence in this case implies that this hypothesis is essentially correct. The only serious conflicting evidence comes from the work with Brattleboro rats. It is hoped that further research will resolve these discrepancies or result in a suitably modified hypothesis.

Interleukin-1 interaction with neuroregulatory systems: selective enhancement by recombinant human and mouse interleukin-1 of in vitro opioid peptide receptor binding in rat brain

Interleukin-1 (IL-1) exerts a wide variety of biological effects on various cell types and may be regarded as a pleiotropic peptide hormone. Biological evidence suggests that IL-1 participates in the modulation of central nervous system physiology and behaviour in a fashion characteristic of neuroendocrine hormones. In this investigation, recombinant (r) human (h) IL-1 and r mouse (m) IL-1 were examined for their modulation of opioid peptide receptor binding in vitro. Experiments were performed on frozen sections of rat brain. Receptor binding of radiolabeled substance P and of radiolabeled neurotensin were not significantly affected by the presence of rIL-1s. Recombinant IL-1s, however, significantly enhanced specific binding of 125I-beta-endorphin (125I-beta-END) and of D-ala2-(tyrosyl-3,5-3H)enkephalin-(5-D-leucine) (3H-D-ALA), equipotently and in a concentration-dependent manner with maximal activity occurring at a concentration of 10 LAF units/ml. The increased binding of 125I-beta-END and 3H-D-ALA was blocked steroselectively by (-)-naloxone and by etorphine, suggesting detection of opiate receptors. In addition, brain distribution patterns of receptors labeled in the presence of rIL-1s corresponded to patterns previously published for opiate receptors. Autoradiographic visualization of receptors revealed that rIL-1s in the different areas of the brain exert their effect on opioid binding with comparable potencies. The data suggest that certain central nervous system effects of IL-1s may be mediated by their selective interaction with opiatergic systems at the receptor level.(ABSTRACT TRUNCATED AT 250 WORDS)

Antipyresis due to centrally administered vasopressin differentially alters thermoregulatory effectors depending on the ambient temperature

The intracerebroventricular (i.c.v.) administration of arginine vasopressin (AVP), in the febrile rat elicits an antipyresis at cold, warm and neutral ambient temperatures. These experiments were conducted, therefore, to elucidate the thermoregulatory effector mechanisms responsible for this antipyretic effect. At 25 degrees C, AVP-induced antipyresis was mediated by tail skin vasodilation while metabolic rate was unaffected. At 4 degrees C, the antipyresis produced by AVP was approximately double that seen at 25 degrees C. This effect appeared to be mediated exclusively by inhibition of heat production since the metabolic rate decreased markedly following AVP. This antipyresis at 4 degrees C was accompanied by cutaneous vasoconstriction. At 32 degrees C, neither vasomotor tone, metabolic rate nor evaporative heat loss could be shown to contribute to the small antipyretic effect elicited by AVP. We conclude from these data that i.c.v. AVP is producing antipyresis by affecting the febrile body temperature set-point mechanism since the thermoregulatory strategy to lose heat varies at different ambient temperatures and the decrease in body temperature cannot be shown to be due to changes in a single effector mechanism.

The antipyretic effects of centrally administered vasopressin at different ambient temperatures

The antipyretic response to arginine vasopressin (AVP) was investigated at 3 ambient temperatures using unanesthetized freely behaving male rats. Responses of non-febrile and febrile rats to intracerebroventricular (i.c.v.) injections of AVP and s.c. injection of indomethacin were observed at cold (4 degrees C), thermoneutral (25 degrees C) and warm (32 degrees C) ambient temperatures. In agreement with previous reports i.c.v. AVP at 25 degrees C decreased brain temperature of febrile but not non-febrile rats. This antipyretic effect was also observed at the warm ambient temperature and during cold exposure. Responses to s.c. indomethacin were qualitatively similar to i.c.v. AVP at neutral and warm temperatures. In the cold, however, indomethacin decreased the brain temperature of both non-febrile and febrile animals, although unlike AVP, brain temperature of non-febrile animals were decreased somewhat more than that of febrile animals. These data show that AVP decreases brain temperature of febrile more than non-febrile rats at all ambient temperatures and may therefore be acting partially on febrile set point. It is likewise clear that AVP affects specific effector mechanisms since antipyretic effects were of different magnitudes at different ambient temperatures. The observation that AVP and indomethacin have qualitatively similar effects on fever at the 3 ambient temperatures suggest that they may act via a common neural pathway.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

Potent stimuli for vasopressin release, hypertonic saline and hemorrhage, cause antipyresis in the rat

Two potent stimuli for AVP release into the blood, hemorrhage and hypertonic saline, were evaluated for their antipyretic effects in the rat. Hemorrhage of 20% of estimated blood volume reduced brain temperature of febrile but not afebrile rats confirming earlier research in the sheep. Hypertonic saline was also antipyretic in the rat. Hypertonic urea was somewhat less antipyretic whereas hypertonic glucose had no effect on febrile temperatures. AVP release into the peripheral circulation showed the relationship saline greater than urea greater than glucose and parallelled the antipyretic effectiveness of these solutes. The antipyresis caused by hypertonic saline was not significantly different in rats passively immunized intravenously with AVP antiserum than in rats which received hypertonic saline alone. These results provide indirect evidence that endogenous AVP is released in the brain following hemorrhage or hypertonic challenge and that this endogenous AVP can affect central febrile pathways.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published since 1979, but data from many earlier papers are also tabulated.

Perfusion of vasopressin within the rat brain suppresses prostaglandin E-hyperthermia

These experiments were undertaken to determine whether arginine vasopressin (AVP) could suppress a prostaglandin hyperthermia and to localize sites of these actions in the rat. Prostaglandin E2 (PGE2) sensitive sites were localized in the ventral-septal area by microinjecting 200 ng/0.5 microliter of prostaglandin E2. During perfusion with an artificial CSF, PGE2 injected into the lateral cerebral ventricle evoked a hyperthermia of more than 1 degree C. Perfusion of 6.5 micrograms/ml of AVP markedly attenuated the PGE2-induced hyperthermia. These results suggest that AVP suppresses PGE2-induced hyperthermia in sites in which PGE2 evokes an increase in core temperature.

The effect of intraseptally applied vasopressin on thermoregulation in the rat

The thermoregulatory effects of intraseptal injection of arginine vasopressin were studied in eight rats in which a thermode and a bilateral cannula had been chronically implanted into the preoptic area and lateral septa, respectively. Intraseptal injection of vasopressin completely suppressed the increase in heat production and body temperature elicited by cooling the preoptic area, but did not appear to affect vasomotor tone. Vasopressin also inhibited heat production in a cold environment, and thus induced a marked drop in core temperature; skin temperature did not, however, fall as much as core temperature suggesting that some vasodilatation occurred. At an ambient temperature in the upper range of thermoneutrality vasopressin had no effect on the thermoregulatory variables studied. It is concluded that vasopressin does not reduce the normal set point temperature and that its main effect is to inhibit thermoregulatory heat production. This effect may explain its antipyretic action.