Effects of Biogenic Amines and TRH on Release of Prolactin and TSH in the Rat1

The effects of a single injection of drugs on serum prolactin and TSH were determinedin male and in estrogen-primed ovariectomized rats. The precursor of serotonin, 5-hydroxytryptophan (5-HTP), produced a significant rise in serum prolactin and TSH, whereas para chloroamphetamine,a depletor of serotonin, elicited a fall in serum prolactin and TSH. α-methylmetatyrosine (α-MMT) and reserpine, both depressors of brain catecholamine (CA) and serotonin levels, evoked significant increases in serum prolactin and reductions in serum TSH. Injection of α-MMT or reserpine together with 5-HTP further elevated serum prolactin but prevented any significant change in serum TSH. This suggests that the ability of α-MMT and reserpine to inhibit TSH release is mediated through a reduction in brain serotonin and not via a decrease in CA. α-methylparatyrosine, which inhibits CA synthesis without altering serotonin, evoked a marked increase in serum prolactin but had no effect on serum TSH. L-dopa administration significantly...