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.