Effect of angiotensin on the pressor response to tyramine in normotensive subjects and hypertensive patients

Arterial blood pressure was recorded directly in 11 normotensive subjects, in 11 patients with essential hypertension and in 10 patients with renovascular hypertension. The pressor response to intravenous injections of norepinephrine, tyramine, angiotensin and ephedrine was compared in these three groups. An infusion of angiotensin was then given and the pressor response to injections of norepinephrine, tyramine, and ephedrine was again measured; in some cases, a comparison of the effects of the cold pressor test was made.

In normotensive subjects, angiotensin infusion caused a significant increase in the responses to tyramine and ephedrine but not to norepinephrine; this occurred with subpressor doses and was unrelated to the level of blood pressure. In patients with renovascular hypertension, the mean pressor responses to injections of tyramine and ephedrine and the ratio of response to tyramine to that to norepinephrine were significantly increased, and the infusion of angiotensin failed to cause any further increase in these responses. In contrast, in patients with essential hypertension, the average response to injections of tyramine was not significantly increased, but during angiotensin infusion the response to tyramine increased as in normotensive subjects. It is proposed that increased response to tyramine, and lack of the potentiating effect of angiotensin demonstrated in renovascular hypertension, may be caused by increased formation of endogenous angiotensin due to renin secretion in this disease.