Effects of natriuretic fractions of human urine on the isolated anococcygeus muscle of the rat.

Freeze-dried samples of human urine were reconstituted and chromatographed on Sephadex G-25 columns. Fractions possessing natriuretic activity were eluted after the salts. Application of aliquots of these fractions, after further freeze drying and reconstitution, to the isolated anococcygeus muscle of the rat produced dose-dependent contractions of this smooth muscle. The potency of these samples in causing contractions was positively correlated with their ability to cause natriuresis in water-loaded conscious rats. Use of selective antagonists of possible agonistic agents showed that the ability of the samples to contract smooth muscle was not due to catecholamines, acetylcholine, 5-hydroxytryptamine, prostaglandin E and angiotensin II.