Abstract:

The effect of progesterone and six other C21 -deoxysteroids on renal sodium retention by male adrenaleotomized rats was compared with the effect exerted by the natural corticoids aldosterone, 11-deoxycorticosterone, and corticosterone. Steroids were active in the following order: aldosterone > 11,19-oxidoprogesterone > 5αH-3,20-pregnanedione ≥ 5βH-3,20-pregnanedione > progesterone = 11-ketoprogesterone > 6,19-oxidoprogesterone = 11-keto- 6,19-oxidoprogesterone ≥ corticosterone. All C21-deoxysteroids, except 11,19-oxidoprogesterone, exhibited parabolic log dose-response functions, indicating an effect that opposes renal sodium retention at high doses. 11,19-Oxidoprogesterone and the natural corticoids exhibited normal, exponential, log dose-response curves. Diverse geometric parameters related to molecular planarity were calculated and their correlation with biopharmacological properties was attempted. The best linear regression was obtained for correlation of the concavity of log dose-response parabolas (second-order coefficients) of C21-deoxysteroids with the C3=O/ring D angle of these molecules. A good linear regression could also be obtained for correlation of the affinity of C21-deoxysteroids, except 11,19- oxidoprogesterone, for purified type I mineralocorticoid receptors with those angles. The latter correlation deteriorated upon incorporation of the affinity data for the three natural corticoids, due to similar affinities of these hormones for type I mineralocorticoid receptors, but could be restored when the binding data for the unpurified, corticosterone-binding globulin- containing stage of the receptors were considered. In vivo binding data followed the same trend as that for unpurified receptors.