We studied the effect of acute administration of two different calcium channel antagonists - verapamil and nilvadipine - on cell proliferation and steroidogenesis in intact adrenal glands. Verapamil and nilvadipine were administered subcutaneously at three dosage amounts over a period of 24 hours to adult male Wistar rats. Colchicine or vincristine was administered intraperitoneally 22 and 20 hours after the first injection of the calcium channel antagonist, respectively. The animals were sacrificed 24 hours after the initial injection. Plasma corticosterone was measured by radioimmunological assay in trunk blood collected from each animal. The adrenal glands were removed and cell proliferation was measured in each zone of the cortex by a metaphase arrest technique. Mitoses were counted and a mitotic index was calculated. Both verapamil (50 mg/kg) and nilvadipine (1 and 10 mg/kg) significantly reduced plasma corticosterone and cell proliferation in adrenal cortex. The greatest inhibition of mitotic activity was seen in the zona glomerulosa. However, nilvadipine, but not verapamil, also inhibited mitosis in the zona fasciculata. The mitotic index in zona reticularis was very low and remained unaffected by either of the drugs. The study found that acute administration of calcium channel antagonists inhibits cell proliferation and corticosterone secretion of the adrenal cortex.

Keywords: verapami, nilvadipine, Corticosterone, Adrenal Cortex