Natriuretic and smooth muscle contracting activities isolated from human urine

Human urine contains a small molecular weight natriuretic substance and similar material isolated from the kidney inhibits Na/K ATPase. Such action on blood vessels would cause contraction. Human urinary natriuretic material isolated from a Sephadex G-25 column contracted smooth muscle in the rat anococcygeus muscle. Known vasoactive substances could not explain the activity of the natriuretic fraction on the anococcygeus muscle. In subsequent studies the natriuretic fraction from the Sephadex G-25 column was run on a Sephadex G-10 column and natriuretic activity was found before the sodium was eluted. The same fractions inhibited Na/K ATPase but did not cause contraction of the anococcygeus muscle. The fractions which did cause contraction of the anococcygeus muscle were eluted long after the salts and these fractions did not inhibit Na/K ATPase and were not natriuretic. The postulated defect in sodium excretion in hypertensive patients might be related to their low kallikrein excretion. Since ANP stimulates increased kallikrein release in rats and does not inhibit Na/K ATPase, it is suggested that the natriuretic pathway via inhibition of renal Na/K ATPase is independent in the kidney of the kallikrein/kinin natriuretic pathway.