Pulmonary angiotensin-converting enzyme and its inhibition: a historical survey.

Angiotensin-converting enzyme, the peptidase hydrolysing angiotensin I to angiotensin II and first discovered in plasma, has been demonstrated in lung tissue on the luminal surface of endothelial cells lining pulmonary blood vessels. Because converting enzyme is the final activating step in the renin-angiotensin system its inhibition prevents the pressor and other effects of increased renin secretion. Lung converting enzyme activity is inhibited specifically by a nonapeptide (BPP9a:SQ 20 881) contained in Bothrops jararaca venom. This peptide inhibits the pressor effects of injected angiotensin I in humans and lowers blood pressure in patients with high-renin hypertension. Recently a synthetic inhibitor, captopril, was devised which is effective, given orally, in reducing the blood pressure of high-renin hypertensives and of a proportion of hypertensives with normal renin levels. The latter finding suggests that blood pressure may be maintained by renin-dependent mechanisms without increased renin secretion.