Background: The beneficial effect of a low-protein diet on the course of renal failure after ablation nephropathy in the rat is known; also calcium channel antagonists (CaA) and angiotensin I converting enzyme inhibitors (ACEI) have a protective effect. Because even simple energy restriction retards the development of spontaneous or ablation-induced glomerulosclerosis the authors decided to replace the lacking dietary protein in the low protein diet by starch (disaccharide) and by fat (cereal oil) and compare these two low-protein diets as to their effect on the development of chronic renal failure (CRI) caused by surgical removal of 5/6 of renal parenchyma (5/6 NX).
Methods and results: In Wistar rats just after weaning, 5/6 of renal parenchyma were removed surgically. Thereafter, the rats were fed either a "high-protein" (21%) or two types of a "low-protein" (6%) diet, in one of the latter, the lack of protein was substituted by saccharide, in the other by fat making the substitution "isocaloric" in either case. In all three diet groups, subgroups drinking either tap water or water containing either the ACE-inhibitor enalapril (ena) or the calcium antagonist diltiazem (dil) or both (ena+dil) were formed. On the high-protein diet, an increase in the weight of kidney remnants, in proteinuria and in systolic blood pressure (SBP) was seen. This was prevented by feeding either type of the low-protein diet but also by ena and ena+dil. Ena and ena+dil not only prevented the increase in SBP but actually lowered it significantly. Dil alone also had a SBP-lowering action but offered no protection from kidney hypertrophy and it significantly. Dil alone also had a SBP-lowering action but offered no protection from kidney hypertrophy and proteinuria. No additive protective action of ena+dil or ena+low-protein or ena+dil+low-protein was seen suggesting that the lower limit of these protective actions was reached by the low-protein diet alone. There was no substantial difference between either type of low-protein diet except a small and transient decrease in body weight in the first week on a fat-rich diet.
Conclusions: In the described experiments and with the set-up used the low-protein diet had no effect on the plasma creatinine and urea levels nor on creatinine clearance. The weight of the kidney remnants and proteinuria were significantly higher in animals on a high-protein diet who drank water or water with diltiazem. These changes were suppressed by administration of angiotensin converting enzyme inhibitors either alone or combined with diltiazem. A low- protein diet (both types tested) as well as angiotensin converting enzyme inhibitors improve the course of chronic renal failure in ablation nephropathy in the rat; the authors did not prove an additive effect of the combination of this diet with angiotensin converting enzyme inhibitors.