Calcium antagonists and hormone release: effect of nifedipine on luteinizing hormone-releasing hormone and thyrotropin-releasing hormone-induced pituitary hormone release.

In vitro evidence suggests that calcium is involved in the release of anterior pituitary hormones. Therefore, we studied the effect of the slow calcium channel blocker or calcium antagonist nifedipine on the FSH and LH responses to LRH and the TSH and PRL responses to TRH in vivo. Nine normal male subjects were studied on two occasions, and nifedipine (20 mg, by mouth, or matching placebo) was administered in a randomized single blind manner. Blood pressure and heart rate were measured at 0 and 30 min. The patients then received TRH (200 micrograms) and LRH (100 micrograms) iv. Blood levels of FSH, LH, TSH, and PRL were measured by RIA at 0, 30, 50, 60, and 120 min. Nifedipine lowered diastolic blood pressure significantly (--12 +/- 8 mm Hg; P less than 0.005) and increased heart rate (+ 17 /*- 10 beats/min; P less than 0.005), but had no effect on either baseline hormone levels or the incremental response of any hormone to its secretagogue. In contrast to the results of previous studies with verapamil, nifedipine does not inhibit the release of pituitary hormones. More information is required on the precise intracellular actions of these drugs before they can be used to study the role of calcium in hormone release. Nifedipine, however, may be less likely to influence pituitary function than verapamil.