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 blo cker, verapamil (0.0833 mg/min for 2-3 h after a 5 mg bolus) on prolac tin (PRL) and thyrotrophin (TSH) circulating levels were assessed in 7 normal subjects and in 17 patients with hyperprolactinemia (11 with p rolactinoma and 6 sulpiride-induced). In the normal group a non-signif icant increase in PRL levels occurred (mean+/-SEM= 11.7+/-2.9 mu g/l v erapamil 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 o n verapamil vs. 9.0+/-0.6 mU/l on saline, p = 0.01. In the hyperprolac tinemic 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 t he 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 ob served. The authors discuss the possibility that the divergent effects of verapamil in hyperprolactinemia of different etiologies could be r elated to the balance between dopamine and calcium channel effects on hypothalamus and/or pituitary.