A smooth muscle active factor isolated from renal cortex of the rabbit

Homogenates of rabbit renal cortex contained a water-soluble material with striking activity on smooth muscle derived from the rabbit aorta, rat stomach, and guinea pig ileum--but not rat colon or chick rectum. Evidence derived from the spectrum of its pharmacologic activity, the influence of specific competitive antagonists on the smooth muscle responses to the factor, the influence of proteolytic enzymes and its elution position during molecular sieve filtration on Sephadex G-10 made it unlikely that the factor was a prostaglandin, renin, angiotensin, a catecholamine, serotonin, bradykinin, a nucleotide, a small organic product of local metabolism, or a small ion. The agent was not found in extracts of renal medulla, spleen, myocardium, or lung. The smooth muscle response to the factor was blocked by phenoxybenzamine. The renal cortical factor in subthreshold concentration also potentiated responses of the rabbit aorta to angiotensin and norepinephrine. The factor's intrinsic activity and ability to potentiate the smooth muscle actions of endogenous vasoconstrictors make it a candidate as a mediator of smooth muscle responses in a number of states.