Inhibition of the aldosterone-suppressant activity of atrial natriuretic factor by progesterone and pregnancy in rats.

Angiotensin II (AII) caused concentration-dependent increase in aldosterone secretion by dispersed zona glomerulosa cells from non-ovariectomized (non-OVX) and ovariectomized (OVX) rats treated with the vehicle (peanut oil), beta-estradiol (0.1 mg/kg/d x 3) or progesterone (2 mg/kg/d x 3); this effect of AII was greater on cells from progesterone- than from estrogen-treated animals. In contrast, atrial natriuretic factor (ANF) was 100- to 1,000-fold less effective in suppressing AII-stimulated aldosterone production by cells from progesterone-treated (both non-OVX and OVX) and pregnant (17-20 day) rats than by cells from nonpregnant controls and estrogen-treated animals. To our knowledge, this is the first demonstration of an inhibition of an important action of ANF by another hormone and our data suggest that increased circulating levels of progesterone during pregnancy produce a relative refractoriness to the aldosterone-suppressant activity of ANF, which favors fluid/salt expansion.