Intracerebroventricular taurine in rabbits: effects of normal body temperature, endotoxin fever and hyperthermia produced by PGE1 and amphetamine.

Abstract

Intracerebroventricular (i.c.v.) injections of taurine into rabbits resting at an ambient temperature (Ta) of 10.degree. or 23.degree. C caused hypothermia but at 30.degree. C ambient temperature, rectal temperature was unchanged. An i.c.v. bolus of 0.5 mg taurine immediately followed by a slow infusion of taurine (0.01-0.2 mg/min) into rabbits at 23.degree. C ambient temperature caused sedation and peripheral vasodilation and blocked the febrile response to Salmonella typhosa endotoxin (1 .mu.g/kg i.v.). Sustained fevers, characteristic of fevers caused by central administration of pyrogens, developed after taurine infusions were stopped. Control infusions of taurine at the same rates in the same rabbits when they were afebrile had little effect on rectal temperature. An i.c.v. injection of 0.5 mg taurine reduced the hyperthermia caused by prostaglandin E1 (PGE1; 2 .mu.g) given i.c.v. A dose of 5.0 mg not only blocked PGE1 hyperthermia but also caused marked hypothermia. Bilateral injections of taurine into the preoptic/anterior hypothalamic region, at sites where injections of S. typhosa endotoxin caused long-lasting fevers, had no effect on rectal temperature. Similar injections into the reticular substance of the medulla oblongata, in the region believed to be concerned with a secondary temperature control function, were also without effect on body temperature. Taurine (0.5 and 5.0 mg, i.c.v.) had no consistent effect on hyperthermia induced by amphetamine (2 mg/kg, i.v.). The hypothermic effect of taurine is not due to an action on the central neuron pool or pools concerned with the integrative control of thermoregulatory effectors. This amino acid appears to inhibit neuronal activity in efferent pathways which control peripheral vasomotor tone and heat production; it also appears to depress the level of arousal. Taurine delays the onset and extends the duration of endotoxin-induced fever, perhaps by 2 separate actions: by inhibiting activity in central thermoregulatory pathways and by promoting accumulation of endogenous pyrogen in the brain.