Natriuretic Effect of Angiotensin in Dogs Revealed after Administration of Reserpine and Guanethidine

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Abstract
In untreated dogs anesthetized with morphine-chloralose, a small dose of angiotensin (0.0375 µg/kg per min) produced a large reduction in renal blood flow, a smaller reduction in glomerular filtration rate and an antinatriuresis. A graded change in the excretion of sodium in response to angiotensin occurred after the successive administration of reserpine and guanethidine. In reserpinetreated dogs, angiotensin did not produce an antinatriuresis, whereas in the same dogs after giving guanethidine, a natriuresis occurred in response to angiotensin (from a control of 60 to 189 µEq Na/min). The effects of angiotensin on blood pressure and glomerular filtration rate were similar in all dogs. The renal vasoconstrictor effect of angiotensin was decreased in 3 of 8 dogs after guanethidine. At the high dose of angiotensin (0.375 µg/kg per min), the natriuresis was larger (from a control of 75 to 353 µEq Na/min) and was unrelated to changes in glomerular filtration rate or renal blood flow. In reserpine- and guanethidine-treated dogs, angiotensin increased sodium excretion sufficiently during renal arterial constriction to produce a large reduction in renal blood flow and the filtered load of sodium. These results suggest that angiotensin has a renal tubular action that is uncovered by sympathetic blockade produced by reserpine and guanethidine.

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