CARDIOVASCULAR ACTIONS OF ANGIOTENSIN IN MAN

Angiotensin exerts a direct action on the smooth muscle of the blood vessels of the human hand and forearm, the latter being the more sensitive. In addition, angiotensin has a central sympathetic stimulating action which, in the case of the hands and feet, is responsible for all of the vasoconstriction seen on intravenous administration. The central action does not play a significant part in the pressor effect of angiotensin given intravenously for short periods of time. In contrast to observations in animals, angiotensin in man does not appear to cause release of adrenal medullary hormones, nor does it act on the peripheral sympathetic nerve endings to discharge the transmitter. Angiotensin causes a modest potentiation of the response of the hand vessels to intra-arterial noradrenaline, which is, however, much less marked than that seen with the isolated perfused digital artery. The blood vessels of the hands of patients with renovascular hypertension show a very marked reduction in sensitivity to angiotensin, whereas the sensitivity in patients with essential hypertension is within the normal range. The phenomenon of tachyphylaxis to angiotensin is widely recognized in animals and isolated preparations, but its occurrence or significance has not been investigated in man. © 1969.