[Arguments for the existence of an endogenous inhibitor of renal Na-K ATPase with steroid structure and natriuretic action].

In order to explain the opposite effect of 6,7-dihydroxylated isomers of 6, 7 - dihydrocanrenone on the urinary sodium and potassium excretion, we have tested the effect of these substances isolated from human urine on the Na(+)-K+ pump from different tissue preparation: rabbit kidney slices as well as NA-K ATPase purified from the kidney. Our results show an inhibition of pump as well as enzyme activity by the 6 beta 7 alpha isomer while the 2 other isomers are either uneffective or slightly stimulating. The 6 beta 7 alpha dihydroxy-6, 7-dihydrocanrenone could be one of the plasma ouabain-like substance incriminated in the pathogenesis of volume-expanded hypertension.