Blockade of prostaglandin E1 hyperthermia by sodium salicylate given into the ventral septal area of the rat brain

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.

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.

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.

Sodium salicylate: alternate mechanism of central antipyretic action in the rat

Infusion of sodium salicylate (50.0 or 100.0 micrograms/microliters) into the ventral septal area (VSA) of the rat brain suppressed Prostaglandin-E1-induced hyperthermia. Infusion of artificial cerebrospinal fluid (aCSF) or 10.0 micrograms doses of salicylate did not. The suppression of intracerebroventricularly-induced (icv) Prostaglandin E1 (PGE1) hyperthermia was not due to a hypothermic action of salicylate since salicylate infusions given during cold exposure (10.0 degrees C) did not lower core body temperatures. A possible interaction between salicylate and endogenous arginine vasopressin (AVP) was investigated. Infusion of both salicylate (50.0 micrograms/microliters) and either AVP antiserum or AVP antagonist into the VSA resulted in PGE hyperthermias occurring at levels which were not different from control levels as opposed to enhanced hyperthermia (antiserum or antagonist alone) or suppressed hyperthermia (salicylate alone). These results are consistent with the notion that sodium salicylate infusions within the VSA enhance AVP action and thus bring about the attenuation of PGE-induced hyperthermia.

Comparative pyrogenic potency of endogenous prostanoids and of prostanoid-mimetics injected into the anterior hypothalamic/preoptic region of the cat

In both pyrogen-induced fever and fever subsequent to acute hypothalamic trauma, pyrexia is believed to be mediated by cyclooxygenase products acting within the anterior hypothalamic/preoptic (AH/PO) region of the brain. The goal of the present study was to assess, through a potency analysis, the likely contributions of various prostanoids to pyrexia production. Prostanoids and prostanoid-mimetics were injected bilaterally into the AH/PO region of conscious, indomethacin pretreated cats, and partial dose-response curves for pyrexic activity were obtained. ED1 degrees doses (doses producing a 1 degree C fever) for PGE2, PGE1 and 6-keto-PGE1 (a metabolite of PGI2 and/or of the PGI2 hydrolysis product, 6-keto-PGF1 alpha) ranged between 2 and 15 pmol. PGF2 alpha and the stable PGI2-mimetics, iloprost and 6-beta-PGI1, required doses of 900-1100 pmol. PGD2 and 6-keto-PGF1 alpha had ED1 degrees doses of 2200-2400 pmol. PGI2, thromboxane (TX) B2 and the TXA2/PGH2-mimetics, SQ26655, 9,11-azo-PGH2 and U46619, were incapable of producing a 1 degrees C rise at the maximum dose of 30,000 pmol. The results offer no support for an involvement in fever of PGF2 alpha, PGD2, TXA2, TXB2, PGH2, PGI2 or 6-keto-PGF1 alpha. Only the 3 E-series prostaglandins were sufficiently potent to merit serious consideration as mediators of pyrexia. Of these, only PGE2 is known to be produced in abundance by cat brain; no information is available regarding PGE1 production, and our results with PGI2 and 6-keto-PGF1 alpha indicate that cat brain may not synthesize 6-keto-PGE1. The results thus suggest an important role for PGE2 in fever production in the cat and are compatible with an involvement of PGE1.