Two major hormonal peptide systems appear to play opposite roles in the regulation of electrolyte balance and blood pressure, so that their imbalance might be responsible for cardiovascular and salt-retention disorders affecting a large fraction of the population (1). The first one is the reninangiotensin-aldosterone system, whose critical role in sodium retention and vasoconstriction was largely evidenced through the use of inhibitors of the membra~ne metallopeptidase angiotensin-converting enzyme (ACE; EC 3.4.15.1) (2, 3). These drugs, which prevent the formation of angiotensin II, a vasoactive, antidiuretic, and antinatriuretic peptide, and decrease blood pressure and aldosterone secretion, have gained wide application in the treatment of essential hypertension and congestive heart failure. The second hormonal system is constituted by the atrial natriuretic factor (ANF), a peptide secreted by the heart into the circulation to decrease blood pressure, raise the urinary excretion of water and sodium, and lower plasma renin and aldosterone levels (4). Recently, the role of another metallopeptidase, enkephalinase (EC 3.4.24.11, membrane metalloendopeptidase), in the inactivation of endogenous ANF was shown by the effects of inhibitors (reviewed in ref. 5). These drugs enhance the circulating level of the hormone in healthy volunteers as well as in patients with congestive heart failure or cirrhosis; induce diuresis, natriuresis, and urinary excretion of cGMP (6-10); and may exert antihypertensive activity (11).Hence it appears that two cell surface, zinc-containing peptidases play a key role in the activation or inactivation pathways of the two hormonal systems. Although many compounds are highly selective inhibitors of either ACE or enkephalinase, some mercaptoalkyl inhibitors display limited but significant crossreactivity toward the two peptidases (12,13). This partial overlap suggested that a careful analysis of structure-activity relationships would enable the design of a single molecular structure able to potently inhibit both enzymes in vivo and, thereby, lead to a class of potentially useful cardiovascular agents blocking both the generation of angiotensin II and the inactivation of ANF.We have now designed such mixed inhibitors which interact with the two peptidases at nanomolar concentrations in vitro and at low dosage per os. These drugs elicit the characteristic actions ofthe two classes ofenzyme inhibitors: prevention of angiotensin I-induced hypertension, protection of ANF, enhancement of diuresis and natriuresis, and increase in urinary cGMP excretion.
