Comparison of the effects of central administration of serine and glycine on body temperature of the rabbit.

In previous research, intracerebroventricular (ICV) injection of serine (1-4 mg) caused dose-related hypothermia in rabbits and reduced rises in body temperature caused by leukocytic pyrogen (LP) and prostaglandin E2 (PGEs). Since serine is the major precursor of the putative neurotransmitter glycine, these effects of serine may be due to its conversion to glycine. To assess this possibility, glycine was administered centrally to see if its effects on body temperature are similar to those of serine. ICV injections of glycine (0.25-1.0 mg) caused dose-related decreased in body temperature in a 10 degrees C environment but had no significant effect at 23 degrees C. Glycine (1 mg) delayed the normal rise in temperature in 30 degrees C environment and reduced LP fever and PGE2 hyperthermia. ICV glycine and serine in combination were, however, subadditive in producing hypothermia, which suggests that these amino acids act at different central sites. A difference in the interaction of serine and glycine with strychnine in producing hypothermia also suggests that the action of serine is not entirely mediated by glycine. Since serine and glycine have similar effects on normal body temperature and fever some portion of the effects of serine may be caused by its conversion to glycine. The subadditivity data and the difference in temperature effects when the amino acids are given with strychnine suggest that serine and glycine probably have separate central sites of action.