Actions of two aldosterone antagonists on cat perfused kidneys

The actions of a closed-ring [spironolactone, SC-9420, beta-(7alpha-acetylthio-17beta-hydroxy-3-oxoandrost-4-en-17alpha-yl)propionic acid lactone] and of an open-ring [SC-11480, potassium beta-(17beta-hydroxy-3-oxoandrosta-1,4-dien-17alpha-yl)propionate] spirolactone have been examined on the cat perfused kidney, in concentrations ranging from 5 to 20 mg per 150 ml. of blood. Both compounds had weak aldosterone-like effects and caused antidiuresis with retention of sodium, potassium and chloride. The urinary changes they induced summed with those of aldosterone, without competition. Neither spironolactone nor SC-11480 affected renal blood flow or glomerular filtration rate. Both compounds antagonized the reduction in renal vascular resistance caused by aldosterone in these preparations.