EFFECT OF CARBIDOPA ON PROLACTIN, GROWTH-HORMONE AND CORTISOL SECRETION IN MAN

Serum prolactin [PRL], growth hormone [GH] and cortisol [F] levels were examined in normal volunteers following administration of carbidopa, a peripheral decarboxylase inhibitor. Twenty-four hour urinary tryptamine levels dropped markedly indicating that inhibition of decarboxylase was effective. PRL levels rose while GH and F remained unchanged. Since the tuberoinfundibular dopamine nerve terminals lie outside the blood brain barrier, these neurons may be involved in PRL but not in GH or F regulation. These findings are compatible with 2 alternate hypotheses.sbd.either dopamine is a physiologic prolactin inhibiting factor (PIF) or tuberoinfundibular dopamine neurons regulate PIF release.