Metoclopramide-mediated prolactin secretion in patients with idiopathic hypogonadotropic hypogonadism: effect of testosterone therapy.

The secretion of prolactin (PRL) after intravenous metoclopramide was evaluated in six prepubertal subjects with idiopathic isolated hypogonadotropic hypogonadism before and after repeated testosterone (T) injections. The PRL response to metoclopramide was markedly blunted before T treatment, but both the basal and metoclopramide-stimulated PRL secretion became normal after 4 to 15 months of intramuscular T enanthate, although in three of the subjects, serum T was low at the time of the repeat study. These results confirm that the pituitary lactotrophs are normal in this disorder and suggest that the attenuated response observed in the untreated patients is due to the chronic and persistent exposure of the lactotrophs to an environment low in T. The effect of exogenous T on the lactotrophs persists for several weeks after T is discontinued.