EFFECTS OF INTRAVENTRICULAR TAURINE, HOMOTAURINE AND GABA ON SERUM PROLACTIN AND THYROTROPIN LEVELS IN FEMALE AND IN MALE-RATS

Serum prolactin and thyrotropin levels of conscious, unrestrained male and female rats were compared after intracerebroventricular (i.c.v.) administration of taurine, gamma-aminobutyric acid (GABA) and homotaur ine. The amino acids studied had no clear effect on serum basal thyrot ropin levels in male or female rats. All amino acids elevated serum pr olactin levels in female rats at the dose of 5 mu mol/rat; homotaurine by about 18-fold, taurine and GABA by 3-fold. Only homotaurine elevat ed serum prolactin of male rats at this dose, but its effect was less pronounced (p < 0.01) in male than in female rats. Although homotaurin e was clearly more potent than the two other amino acids, at the dose of 10 mu mol/rat taurine and GABA also elevated serum prolactin in mal e rats. These findings show that there are gender-related differences in the responses of serum prolactin levels to homotaurine, taurine and GABA in rats. The tuberoinfundibular dopaminergic pathway, which exer ts tonic inhibitory influence on prolactin secretion, is sexually diff erentiated. Hence the gender-related differences in the effects of the amino acids on prolactin secretion suggest that they might inhibit do pamine release from the median eminence. In case of homotaurine, the g ender effect was most pronounced. The less clear dependence of GABA's effect on the gender is in accordance with the suggestions that GABA i nfluences the secretion of serum prolactin by more than one mechanism.