AJP - Endocrinology and Metabolism, Vol 272, Issue 1 E18-E24, Copyright © 1997 by American Physiological Society
Effects of dihydropyridines on aldosterone secretion in adrenal capsule preparations from pregnant rats
M. Brochu, S. Picard, S. Jodoin and J. St-Louis
Research Center, Sainte-Justine's Hospital, Montreal, Quebec, Canada.
The primary aim of this study was to determine when sensitivity in the
aldosterone response to extracellular potassium (K+) decreases during
pregnancy. Second, it tested the hypothesis that calcium channel
alterations occur in the adrenal cortex during pregnancy. The decreased
sensitivity to K+, observed at 22 days of gestation, was not evident at 15
days and between 18 and 36 h postpartum. Increases in extracellular calcium
concentration heightened sensitivity to K+ in adrenal capsule preparations
derived from nonpregnant rats but had no effect in pregnant animals. The
influence of nifedipine and BAY K 8644 (blocker and activator,
respectively, of voltage-operated calcium channels) on the aldosterone
response to K+ and to adrenocorticotropic hormone (ACTH) was studied.
Sensitivity to K+ in nonpregnant rats decreased in the presence of
nifedipine and became similar to that in pregnant rats. Responses to ACTH
were not affected by nifedipine. BAY K 8644 produced a larger increase in
sensitivity in adrenal capsule preparations from pregnant than from
nonpregnant rats, leading to superposition of the two dose-response curves
to K+. These results indicate that voltage-operated calcium channels
involved in aldosterone secretion are functionally impaired during
pregnancy.
