Inhibition of brain catecholamine synthesis and release of prolactin and luteinizing hormone in the ovariectomized rat.

The effects of alpha-methyl-p-tyrosine (alpha-MT) on brain catecholamine synthesis and plasma prolactin and luteinizing hormone levels were determined in ovariectomized rats to ascertain whether the release of either hormone from the anterior pituitary is dependent on the release of newly synthesized dopamine and norepinephrine. Doses of alpha-MT ranging from 3.15 to 25 mg/kg were administered via a carotid cannula to unrestrained ovariectomized rats. Within 10 minutes, alpha-MT caused a significant dose-related increase in plasma concentrations of prolactin which became maximal 20 to 25 minutes after the injection. Plasma levels of luteinizing hormone were not affected. Alpha-MT caused a dose-related decrease in the accumulation of 3-H-norepinephrine and 3-H-dopamine in the brain after the administration of 3-H-tyrosine. The time course of the inhibition of catecholamine synthesis closely paralleled the increase in plasma prolactin concentration. Alpha-MT had no effect on endogenous catecholamines. The results suggest that catecholamine-containing neurons exert a tonic inhibitory influence on the release of prolactin in ovariectomized rats.