Serum prolactin in patients with Laron-type dwarfism: effect of insulin-like growth factor I.

Prolactin (PRL) secretion was studied in Laron-type dwarfism (LTD) patients (8 children and 9 adults) in basal condition, after acute insulin-like growth factor (IGF-I) or TRH injections and during 2 months of daily IGF-I treatment. Basal PRL was repeatedly higher (12.6 +/- 1.6 micrograms/l) than that in control subjects (7.6 +/- 1.2 micrograms/l, p < 0.05). Acute IGF-I injection caused an immediate slight decrease in serum PRL and growth hormone (GH), followed by a progressive rise to mean peak levels of 33.3 +/- 4.5 micrograms/l again parallel to serum hGH which rose to 86 +/- 20 micrograms/l--a response to the IGF-I-induced hypoglycemia. Intravenous TRH in LTD children induced a marked response in serum PRL, similar to that registered in estrogenized adult females. Serum PRL did not show consistent changes during chronic IGF-I treatment. It is suggested that the higher-than-normal PRL levels and release in LTD patients are due to a drift phenomenon of the mammosomatotropes which produce large amounts of hGH.