Agents which block the action of the renin-angiotensin system.

• The role of the renin-angiotensin system in the control of arterial blood pressure and aldosterone secretion has been studied extensively in homeostasis, hypertensive disease, and edematous states. For many years it has been realized that the availability of effective blocking agents for renin or for angiotensin II might help greatly in the study of this system and might have important value in the treatment of conditions such as renal hypertension and heart failure. During the past few years, an increasing number of blocking agents for the reninangiotensin system have been developed. These agents act at one of three sites: (1) they block the action of renin in plasma, (2) they prevent converting enzyme from forming angiotensin II from angiotensin I, or (3) they block the receptor sites for angiotensin II in arteriolar smooth muscle and adrenal cortex. In addition, adrenergic blocking agents such as propranolol decrease the release of renin from the renal juxtaglomerular cells. This review is concerned only with the agents which block the action of the renin-angiotensin system, not with those that decrease the release of renin. The new observations with blocking agents have helped solve several specific problems under investigation, and, in addition, new important functions of the renin-angiotensin system have been uncovered. For example, it is now recognized (1-5) that in low output states angiotensin II acts directly on the peripheral arterioles including the renal vasculature to increase peripheral resistance, decrease renal blood flow, and maintain arterial blood pressure. In this review, the recent findings have been collated to present this new knowledge on the physiology of angiotensin II, to evaluate the present state of our knowledge on such important problems as the pathogenesis of experimental renal hypertension, and to stimulate additional research on the physiology of the renin-angiotensin system.