1. Blood pressure and plasma renin activity were studied after bilateral nephrectomy in groups of rats with hypertension caused by unilateral renal ischaemia with the opposite kidney left intact.
2. Although blood pressure showed only a small fall in the first hour after bilateral nephrectomy, plasma renin activity fell rapidly with a half-life of 10 min.
3. Infusion of converting enzyme inhibitor (SQ20881) produced a 26·1% fall in blood pressure 1 h after nephrectomy, 24·0% at 2 h and 4·6% at 6 h.
4. An angiotensin antagonist (Sar1-Ala8-angiotensin II) was infused into hypertensive rats 1 h after nephrectomy; this blocked the vasodepressor action of the converting enzyme inhibitor, indicating that the fall in blood pressure produced by the inhibitor was due to its action upon the renin-angiotensin system.
5. The renin—angiotensin system maintains blood pressure in this model even after plasma renin has fallen to insignificant levels. This supports the view that vascular renin activity has a longer half-life than circulating renin and is important in the control of blood pressure.