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SUMMARYWe measured arterial plasma angiotensin II concentration, renal blood flow, and arterial blood pressure in six conscious dogs during intravenous infusion of angiotensin II (5, 10, and 20 ng/kg per min). The same measurements were made on a different occasion in the same six animals, while they were conscious, before and during constriction of a main renal artery. Arterial blood pressure and plasma angiotensin II rose and renal blood flow decreased in both experiments. The similarity of regressions for plasma angiotensin II concentration and arterial blood pressure in the two experiments strongly suggests that the rise of circulating angiotensin II after renal artery constriction is sufficient to account for the hypertension by its direct pressor action. As discussed, a different mechanism seems likely to be involved in the later stages of renal hypertension. Angiotensin II is more likely to be in the 5-isoleucine form than in the 5-valine form in the dog. In contrast to the rat, plasma concentrations of the heptapeptide (angiotensin III), hexapeptide, and pentapeptide fragments of angiotensin II are low in the dog.THE ROLE of renin in the pathogenesis of hypertension remains uncertain: after renal artery constriction in animals arterial pressure and plasma levels of renin and renin activity increase but thereafter hypertension persists while the renin level falls. "5 Recent experiments with inhibitors of the renin-angiotensin system suggest its involvement in the early stages of renal hypertension.6 '" The purpose of the experiments described here was to determine whether the plasma concentrations of angiotensin II (the vasoactive component of the renin-angiotensin system) also rises in these circumstances and whether the levels reached are sufficient to account for the increase in arterial pressure in the early stages of renal hypertension. Scornik and Paladini 12 used bioassay to show angiotensin blood levels to be high in early stages of renal hypertension, but normal in the later stages.We measured arterial pressure and plasma concentrations of renin and angiotensin II in conscious dogs before and shortly after constriction of the main artery to one kidney; the results were compared with similar measurements in the same animals before and during pressor infusions of angiotensin II. The experiment was then repeated after removal of the contralateral kidney because of evidence (see Discussion) that hypertension of this type is less dependent on renin and angiotensin. To validate the angiotensin assay, we studied the immunoreactive breakdown fragments of angiotensin II in dog plasma and the reactivity of canine angiotensin II with the antisera used. Methods TERMINOLOGYDogs with one renal artery constricted and the opposite kidney removed are described as one-kidney hypertensive dogs; dogs with unilateral renal artery constriction but with the opposite or "untouched" kidney in situ as two-kidney hypertensive dogs. TECHNIQUES FOR EXPERIMENTS ON DOGSSix male mongrel dogs were housed prior to and during the ...

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