CALCIUM AND PROLACTIN SECRETION IN HUMANS - EFFECTS OF THE CHANNEL BLOCKER, VERAPAMIL, IN THE SPONTANEOUS AND DRUG-INDUCED HYPERPROLACTINEMIA

The effects of the intravenous administration of a calcium channel blocker, verapamil (0.0833 mg/min for 2-3 h after a 5 mg bolus) on prolactin (PRL) and thyrotrophin (TSH) circulating levels were assessed in 7 normal subjects and in 17 patients with hyperprolactinemia (11 with prolactinoma and 6 sulpiride-induced). In the normal group a non-significant increase in PRL levels occurred (mean+/-SEM= 11.7+/-2.9 mu g/l verapamil vs. 8.5+/-1.4 mu g/l saline). In this control group the peak response of PRL and TSH to TRH (thyrotrophin releasing hormone) during verapamil or saline was also determined: PRL = 112.0+/-27.0 mu g/l on verapamil vs. 53.6 mu g/l on saline, p = 0.02; TSH 7.1+/-0.7 mu U/l on verapamil vs. 9.0+/-0.6 mU/l on saline, p = 0.01. In the hyperprolactinemic subjects verapamil induced opposite effects on PRL levels, the prolactinoma group exhibiting an increase in the mean values (168.5+/-22.3 mu g/l vs. 150.8+/-23.6 mu g/l on saline, p = 0.04) whereas in the sulpiride-induced there was a reduction in the mean PRL levels (61.1+/-13.8 mu g/l vs. 78.5+/-19.3 mu g/l on saline, p = 0.002). In both groups of hyperprolactinemic patients no effects on TSH levels were observed. The authors discuss the possibility that the divergent effects of verapamil in hyperprolactinemia of different etiologies could be related to the balance between dopamine and calcium channel effects on hypothalamus and/or pituitary.