RESUMO
Plasma aldosterone levels increase markedly during pregnancy, but not in proportion to the rise in plasma renin activity (PRA). We have developed a reliable in vitro method to investigate aldosterone secretion during pregnancy. With this method, we have assessed the potency and effectiveness of ACTH and potassium to stimulate this secretion during pregnancy. Adrenal capsules from pregnant and nonpregnant rats were incubated in 1 ml of culture medium within wells of tissues culture plates. The cortex was transferred every 20 min to another well containing fresh medium with or without ACTH or potassium. Basal and stimulated aldosterone secretions were not significantly affected by time under our experimental conditions. The glands remained responsive to stimulants throughout the study period (360 min). Plasma aldosterone levels and PRA were increased during pregnancy. Basal aldosterone secretion in adrenal cortex suspensions from pregnant rats showed a 1.6-fold increment (P < 0.001) in comparison with nonpregnant controls. The dose-response curves of ACTH were not significantly different between pregnant and nonpregnant animals. However, sensitivity to potassium was significantly reduced during pregnancy, as demonstrated by an elevated ED50 (4.01 +/- 0.08 vs 4.71 +/- 0.07 mM for nonpregnant versus pregnant rats respectively, P < 0.001). These data indicate that adrenal cortex suspensions are a reliable and reproducible way to study aldosterone secretion during pregnancy. They reveal that, during pregnancy, sensitivity of potassium to stimulate aldosterone secretion is decreased while the response to ACTH is not affected.
