FURTHER EVIDENCE THAT PROLACTIN SECRETION IN ADULT FEMALE RATS IS DIFFERENTLY MODIFIED AFTER NEONATAL ESTROGENIZATION OR ANDROGENIZATION - RESPONSES TO METHYSERGIDE, QUIPAZINE, AND PIZOTIFEN

The role of the serotoninergic system in the control of prolactin secretion was investigated in adult female rats treated on the first day of life with estradiol benzoate (EB) (100 mug), testosterone propionate (TP) (25 or 100 mug), or olive oil. Blood of rats was obtained through a chronic intraatrial cannula at 0, 30, 60, 90, and 120 min after the IP administration of the serotoninergic blockers methysergide (0.75, 2.5, and 7.5 mg/kg) or pizotifen (2 mg/kg), the agonist quipazine (3 or 30 mg/kg), or saline. We have found that 1) the anovulatory syndrome induced by EB or 100 mug injection of TP was associated with hyperprolactinaemia, whereas normal prolactin concentrations in plasma were observed in females injected with 25 mug of TP; 2) methysergide administration increased plasma prolactin concentrations in control and androgenized females but not in the estrogenized ones. This different response may be related to the antidopaminergic action of methysergide, because both estrogenized and androgenized females responded similarly after pizotifen injection; 3) after quipazine injection, an initial stimulation was observed in females injected with estradiol or 100 mug of TP, but not in other groups, whereas a delayed inhibition occurred in androgenized females. These results suggest that the effects of estrogenization and androgenization on both the dopaminergic and serotoninergic control of prolactin secretion are qualitatively different.