The continuous estimation of angiotensin formed in the circulation of the dog

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Abstract
The use of the isolated rat colon as a blood-bathed organ is the technique described for detecting changes in angiotensin concentration in the circulating blood of dogs. Partial occlusion of the aorta by a ballon inflated above the renal arteries leads to a contraction of the blood-bathed rat colon. From the experimental evidence, it is concluded that this contraction is due to an increased concentration of circulating angiotensin, brought about by the liberation of renin from the kidneys, which occurs within seconds of reducing the blood pressure to the kidneys and is proportional to the degree of reduction of blood pressure. With a prolonged reduction of renal blood pressure the concentration of angiotensin increases over the first 10-12 min. and then reaches a stable level. After a small hemorrhage angiotensin often appears in the circulation without a concomitant release of catecholamines. Greater hemorrhages induce the secretion of catecholamines as well as of renin. The catecholamine secretion is inhibited by ganglion block, but the renin secretion is not. It is concluded that the secretion of renin by the kidneys in response to a fall of renal blood pressure is a physiological response, probably of importance in homeostasis.