AJP - Endocrinology and Metabolism, Vol 257, Issue 5 E632-E638, Copyright © 1989 by American Physiological Society
Oral verapamil and calcium and vitamin D metabolism in rats: effect of dietary calcium
J. Fox and C. P. Della-Santina
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Prior studies showed that chronic oral verapamil administration increased
plasma immunoreactive parathyroid hormone (irPTH) but decreased
1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels in rats fed a high (1.2%)-Ca
diet. These and other findings suggested that verapamil may induce
target-organ PTH resistance. This study determined the effects of verapamil
(4, 20, or 100 mumol.kg-1.day-1 for 2 wk) in rats fed high (1.2%)-,
low-normal (0.47%)-, and low (0.02%)-Ca diets (higher irPTH levels). With
1.2 and 0.47% Ca diets, verapamil administration was associated with
increases in irPTH (92 and 44%, respectively) and decreases in 1,25(OH)2D3
levels (22 and 21%, respectively), increases in duodenal Ca transport (13
and 8%, respectively), and increases in tibia mineral content (1.3 and
2.8%, respectively). The decrease in 1,25(OH)2D3 levels was caused by
decreased production, not by increased clearance. In contrast, verapamil
was without effect in rats fed the 0.02% Ca diet. Thus severe dietary Ca
deficiency abolished the stimulatory effects of verapamil on irPTH levels,
Ca absorption, and tibia mineral content. Importantly, these results
indicate that verapamil, in contrast to nifedipine, appears not to have
adverse effects on Ca homeostasis in rats, irrespective of dietary Ca
intake.
