1. Complete ligation of the aorta between the origins of the two renal arteries in the rat produces a predictable form of accelerated hypertension. Changes in the blood pressure, plasma renin activity and renal histological lesions have been studied.
2. Group 1 rats and their control group (group 2) received tap water, and group 3 and its control group (group 4) received sodium chloride solution (0·154 mol/l) in place of tap water, for 4 weeks before aortic ligation. In the experimental groups 1 and 3, complete ligation was carried out. In groups 2 and 4 the aorta and renal arteries were exposed, but not ligated. Interlobular artery lesions were studied on a blind basis and graded 0–4 according to severity.
3. Groups 1 and 3 developed severe hypertension. In group 1 the raised mean arterial pressure showed a significant correlation with increased plasma renin activity. Both mean arterial pressure and plasma renin activity also showed a significant correlation with changes in interlobular arteries. In group 3 the raised mean arterial blood pressure did not show a significant correlation with the depressed plasma renin activity, or with changes in interlobular arteries. A significant correlation was, however, found between plasma renin activity and interlobular artery lesions in group 3.
4. These results suggest that the renin-angiotensin system may influence renal vascular lesions through some mechanism independent of the blood pressure.