Prolactin concentrations in patients with acromegaly: clinical significance and response to surgery

Basal serum prolactin and growth hormone (GH) concentrations were measured by radioimmunoassay in forty patients with acromegaly. GH concentrations were elevated in all patients studied before treatment and prolactin levels were raised in seven of twenty-six patients. Of the thirty-two patients reviewed after treatment (which in most cases was transsphenoidal hypophysectomy) twenty-five had GH concentrations below 5 ng/ml and twenty-nine had normal prolactin levels. In eighteen patients hormone measurements were made both before and after hypophysectomy: though GH levels fell in all but one, prolactin fell in only six patients. They were not significantly changed in eleven patients. There was no correlation of GH and prolactin either before or after surgery. Seven patients had greatly elevated prolactin levels and in four of these there was evidence of upward extension of a pituitary tumour on air encephalogram (AEG). Only one patient with a normal prolactin level had an abnormal AEG. Two patients with elevated prolactin concentrations and normal AEGs had a parallel fall of prolactin and GH in response to surgery. Four of the five hyperprolactinaemic men complained of loss of libido: in three gonadotrophin concentrations before and after treatment were normal. We conclude that there is no overall correlation of GH and prolactin levels in patients with acromegaly. Seven of twenty-six untreated patients (27%) had hyperprolactinaemia. We suggest that in these patients a raised prolactin level may be due either to interference with the normal inhibitory control mechanism of prolactin by suprasellar extension or, more rarely, to secretion of both GH and prolactin by the tumour itself. A high prolactin concentration may be the cause of the impotence of which some patients with acromegaly complain.