Prolactin.

Prolactin exists in man as a distinct and separate anterior pituitary hormone from growth hormone. It is important in lactation and the control of gonadal function, although it may have a much wider and basic metabolic role, similar to its role in lower forms. In clinical endocrinology it is important as an index of pituitary and hypothalamic diseases; thus prolactin levels are elevated in association with these conditions and this reflects the normal tonic inhibitory hypothalamic control of prolactin by PIF; DA is the most important PIF. Hyperprolactinaemia causes hypogonadism in both men and women; it may present in women with amenorrhoea, oligomenorrhoea, polymenorrhoea, regular cycles with anovulation or a defective luteal phase, and impotence in men. In either sex galactorrhoea is reported to occur in only 30 per cent of patients. Neurotransmitter therapy, with dopamine agonists which act as functional analogues of PIF, restores prolactin levels to normal and leads to a return of normal gonadal function. The mechanism of the hypogonadism is not clear and is discussed together with the problems associated with inducing pregnancy in these patients, who may harbour microadenomata of the pituitary.