Inhibition of prolactin secretion by moderate and high doses of testosterone.

The effects of different doses of testosterone on basal and stimulated secretion of prolactin (PRL) were investigated. Intact female mice of the S/W strain were injected sc with 0, 1, 10, 20, 50, 250, 500, 1000, 2500, or 5000 micrograms of testosterone propionate (TP) once daily for 4 weeks. Serum testosterone concentrations of TP injected mice rose 2- to 5-fold above those of controls at 1- to 50-micrograms doses, and 25- to 600-fold over controls in mice given higher doses of the steroid. Administration of 1 microgram of TP, the lowest dose tested, had no significant effects on basal serum PRL concentrations and only slightly inhibited the release of PRL induced by perphenazine, but the weight and PRL concentration of the pituitary gland were significantly depressed. However, at doses of 10, 20, and 50 micrograms TP, perphenazine-induced PRL release, pituitary PRL concentration, and pituitary gland weight were all reduced in a dose-related manner. The basal serum PRL concentrations decreased by the time the dose of TP reached 50 micrograms. In contrast, higher doses of TP (250 micrograms and above) reversed the suppression of these parameters: pituitary gland weight and basal serum PRL levels were restored to control levels, whereas pituitary PRL concentrations and perphenazine-induced PRL release were partially restored. These results suggest that administration of moderate and large doses of testosterone may suppress natural episodic and acute releases of PRL.