Fate of angiotensin I in the toad Bufo melanostictus

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Abstract
Summary: The effects of angiotensin I and II on the blood pressure of pithed toads and the disappearance of angiotensin I and II in the perfused organs of the toad were studied. Angiotensin I was relatively inactive on the blood pressure of pithed toads; it exhibited less than 3% of the pressor activity of angiotensin II. Angiotensin I was not converted to angiotensin II during passage through the lungs. There was also no evidence of net conversion during passage through the kidney and hind quarters. During passage through the lungs, 33–50% of angiotensin I was removed and 25–50% was removed during passage through the hind quarters. No loss of activity was detected when angiotensin II passed through the kidneys. Angiotensin II passed through the lungs and kidneys without loss but 25–50% disappeared during passage through the hind quarters. The relatively low pressor activity of angiotensin I together with its lack of conversion to angiotensin II in isolated perfused organs suggest that the converting enzyme is absent in the toad, Bufo melanostictus.