Central administration of serine causes hypothermia and inhibits fever in rabbits

When serine, a precursor of taurine, was injected into the lateral ventricle (ICV), it caused dose-related decreases in rectal temperature of rabbits in a cold environment (10 degrees C) but had little effect in a thermoneutral environment or in the heat (30 degrees C). Induction of fever by IV leukocytic pyrogen was inhibited by serine given ICV in a single injection, in two injections 30 min apart, or when infused for one hour in a thermoneutral environment; a single injection also inhibited fever in the heat. Reduction of body temperature in the cold and prevention of fever development in a thermoneutral environment were associated with vasodilatation of the ears; the inhibition of fever development in the heat, with suppression of vasoconstriction. The hyperthermic response to ICV PGE2 (500 ng) was also inhibited by pretreatment with serine in both thermoneutral and hot environments. When serine and taurine were injected together ICV in a cold environment, the reductions in body temperature were consistent with an additive action of the two amino acids. The increased effects of acute serine injections over infusions of even greater amounts of the amino acid suggest that large doses of serine can influence early inward transport of endogenous pyrogen. Serine appears to inhibit activity in central pathways which mediate both heat production and heat conservation, possibly at the same receptor sites as taurine. Unlike taurine, however, serine infusion does not augment and prolong fever when infusion is stopped and it is unlikely that this amino acid influences inactivation of endogenous pyrogen that reaches the brain.