Absence of suppressive effect of somatostatin on prolactin levels in patients with hyperprolactinemia.

The effect of somatostatin (SRIF: 10 micrograms/min during 120 min) on serum prolactin (PRL) levels was studied in eleven patients with hyperprolactinemia of varying causes: 2 patients with acromegaly; 2 with primary hypothyroidism; 4 with prolactinoma and 3 with drug (sulpiride) induced hyperprolactinemia. During SRIF infusion, no significant change in PRL levels was observed in any of the 4 groups studied except in one female patient with a prolactinoma. The biological activity of SRIF was demonstrated by the significant inhibition (P less than 0.05) of insulin levels seen in all 11 patients (52% fall in relation to basal) without simultaneous modification of glycemia. These data suggest that SRIF does not decrease PRL secretion in most patients with hyperprolactinemia.