Progesterone-cortisol interaction in control of renin activity but not aldosterone.

In addition to its effect of inhibiting adrenocorticotropic hormone (ACTH) secretion, cortisol (hydrocortisone) inhibits the renin-angiotensin system in both fetal and adult sheep. We have found that progesterone attenuates the inhibition of ACTH by cortisol. These studies test whether progesterone interacts with cortisol in control of the renin-angiotensin-aldosterone system. Conscious adult ewes were infused with vehicle, cortisol (4 micrograms.kg-1.min-1), progesterone (0.5 microgram.kg-1.min-1), or cortisol with progesterone for 60 min. Beginning 120 min after the start of the infusion, renin secretion was stimulated by infusing sodium nitroprusside (10 micrograms.kg-1.min-1 iv). Cortisol infusion decreased plasma K+ concentration and reduced the plasma renin activity (PRA) and aldosterone responses to nitroprusside. Progesterone alone had no effect on PRA, aldosterone, or K+. Progesterone reduced the inhibition of PRA, but not aldosterone or K+, by cortisol. The data also indicate that the suppression of renin, as well as the suppression of ACTH, involves receptors or intracellular mechanisms with which progesterone interacts, whereas the inhibition of aldosterone involves a mechanism that progesterone does not affect.