Effect of calcium channel antagonist (nicardipine) on growth hormone and prolactin secretion in pituitary adenomas

: This study was designed to investigate the effect of calcium channel antagonist (nicardipine) on basal and bromocriptine-inhibited GH or PRL secretion in eight patients with pituitary adenomas (six GH producing adenomas and two prolactinomas). GH or PRL was measured in blood collected at intervals for 12 hours after oral administration of nicardipine (Nc) (40 mg) and/or bromocriptine (Br) (2.5 mg) in each case. In vitro, pituitary adenoma cells were incubated in media containing Nc (200 ng/ml) and/or Br (200 ng/ml) over a 72-h period, and then in drugs-free media for three days. Media were collected at 24-h intervals and assayed for GH or PRL. In three of six GH producing pituitary adenomas, GH secretion was inhibited by Nc both in vivo and in vitro. In prolactinomas, PRL secretion was inhibited by Nc in vitro, but in vivo, an increase of plasma PRL levels was observed after Nc administration in one of two cases. In two acromegalic patients and one patient with prolactinoma, Nc reduced the suppression of GH or PRL secretion induced by Br. These findings indicate that influx of extracellular calcium plays an important part in both GH and PRL secretion in functioning pituitary adenomas, and that Nc effects on GH and PRL secretion in pituitary adenomas by blocking of influx of calcium and/or antidopaminergic action. It is considered that the combined administration of calcium channel antagonist (Nc) and Br for acromegalic patients and administration of Nc for patients with prolactinomas should be avoided.