High salt diet ameliorates effects of angiotensin converting enzyme inhibition in spontaneously hypertensive streptozotocin diabetic rats

1. To dissociate the effects on the development of diabetic renal injury of angiotensin converting enzyme (ACE) inhibition per se, and a reduction in systemic blood pressure, we have studied the effects of chronic ramapril treatment in streptozotocin diabetic spontaneously hypertensive rats, with modulation of the hypotensive effect by a high salt diet. 2. Three weeks following uninephrectomy and induction of diabetes with streptozotocin, spontaneously hypertensive rats were allocated to three treatment groups. Groups 1 and 2 received 1% sodium chloride and Group 3 water as drinking solution. Groups 2 and 3 received 0.4 mg/kg per day ramapril in drinking solution over the subsequent 2 month study period. 3. Sodium chloride drinking solution (1%) completely prevented any hypotensive effect of ramapril. Blood pressure was reduced in Group 3 rats over the entire period of study, when compared with Group 2 rats (P less than 0.001). 4. Urinary protein excretion progressively increased in Group 1 and 2 rats, and was significantly reduced (P less than 0.001) in Group 3. After 2 months treatment, urinary protein (expressed as mean and s.e.m.) was 160 +/- 30 mg/day in Group 1, 240 +/- 50 mg/day in Group 2, and 60 +/- 11 mg/day in Group 3. 5. Angiotensin converting enzyme inhibition per se was not associated with a reduced protein excretion in diabetic nephropathy, requiring concomitant control of systemic blood pressure to become renoprotective.