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

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)

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.

Indomethacin-induced urinary flow rate reduction in the ovine fetus is associated with reduced free water clearance and elevated plasma arginine vasopressin levels

OBJECTIVE

The purpose of our study was to explore the urinary responses of the ovine fetus to indomethacin levels comparable with those used therapeutically in the human fetus.

STUDY DESIGN

After a 1-hour control period, chronically catheterized ovine fetuses between 125 and 139 days of gestation were given an intravenous bolus of indomethacin (0.05 mg/kg estimated fetal weight) followed by a 0.0025 mg/kg/min continuous infusion for 5 hours. The experimental group (n = 9) was compared with a vehicle-only infusion group (n = 10).

RESULTS

There was a sustained 55.7% +/- 9.5% (mean +/- SEM) decrease in urinary output by 2 hours of indomethacin infusion (p < 0.00001, analysis of variance). Urinary osmolality, potassium, and chloride concentrations underwent sustained increases during the infusion period (p < 0.005). Free water clearance decreased by 67.5% +/- 12.0% (p < 0.001). Fetal arterial pressure increased only transiently (p < 0.05), and increases in venous pressure (p = 0.013) and heart rate (p < 0.0001) were sustained. Fetal plasma arginine vasopressin concentration increased during indomethacin infusion (p < 0.05) and was correlated with the fall in urinary flow rate and free water clearance (p = 0.002). During vehicle infusion no significant changes were observed in any of the variables.

CONCLUSIONS

Our data indicate that the fetus undergoes antidiuresis when exposed to low levels of indomethacin and that the observed antidiuresis is mediated by a decrease in free water clearance. The reduction in free water clearance may be mediated by increases in plasma arginine vasopressin concentrations.