Brain serotonin turnover in the hypophysectomized rat

Brain serotonin turnover, as measured from the rate of decline of 5-hydroxyindoleacetic acid after pargyline administration, was higher in hypophysectomized rats than in intact age-matched controls. As a consequence brain 5-HIAA concentrations were also increased after hypophysectomy. The increased brain 5-HT turnover was neither dependent on the duration of hormonal deprivation nor it was related to the extent of sexual maturation of the animal when the pituitary ablation was performed. The finding that hypophysectomy markedly affected the disposal of tryptophan both in the plasma and the brain suggest that the increased brain 5-HT turnover found in hypophysectomized rats may be ascribed to an enhanced availability of this amino acid by brain 5-HT neurons.