Diminished prolactin reserve in acromegaly.

Overview

Prolactin (PRL) secretion has been evaluated in twenty acromegalic patients. All had intact LH, FSH, and cortisol levels and normal thyroid function. Five patients had persistent hyperprolactinemia. The remainder had decreased basal PRL levels with impaired PRL responses to TRH and the dopaminergic antagonist metoclopramide (MET). Despite adequate hypoglycemia and an intact cortisol response, there was no PRL rise following insulin hypoglycemia. The imparied PRL response to TRH was evident in treated and untreated patients and was independent of GH levels. Basal hyperprolactinemia may be related to PRL secretion by the tumor cells or interference with the transport of PIF by the tumor. The decreased PRL reserve noted in the majority of the patients may be related to a decrease in lactotrope cell mass or, alternatively, to enhanced dopaminergic activity.