INCREASE OF ALDOSTERONE SECRETION IN ADRENAL-CORTEX SUSPENSIONS DERIVED FROM PREGNANT RATS

Plasma aldosterone levels increase markedly during pregnancy, but not in proportion to the rise in plasma renin activity (PRA). We have deve loped a reliable in vitro method to investigate aldosterone secretion during pregnancy, With this method, we have assessed the potency and e ffectiveness of ACTH and potassium to stimulate this secretion during pregnancy, Adrenal capsules from pregnant and nonpregnant rats were in cubated in 1 ml of culture medium within wells of tissues culture plat es. 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 o ur experimental conditions, The glands remained responsive to stimulan ts throughout the study period (360 min), Plasma aldosterone levels an d PRA were increased during pregnancy, Basal aldosterone secretion in adrenal cortex suspensions from pregnant rats showed a 1.6-fold increm ent (P < 0.001) in comparison with nonpregnant controls, The dose-resp onse curves of ACTH were not significantly different between pregnant and nonpregnant animals, However, sensitivity to potassium was signifi cantly reduced during pregnancy, as demonstrated by an elevated ED(50) (4.01 +/- 0.08 vs 4.71 +/- 0.07 mM for nonpregnant versus pregnant ra ts respectively, P < 0.001). These data indicate that adrenal cortex s uspensions are a reliable and reproducible way to study aldosterone se cretion during pregnancy, They reveal that, during pregnancy, sensitiv ity of potassium to stimulate aldosterone secretion is decreased while the response to ACTH is not affected.