Effects of dietary lipids on renal function of aged rats.

Normal aging is accompanied by renal functional and morphological deterioration and dietetic manipulation has been used to delay this age-related decline. We examined the effects of chronic administration of diets containing 5% lipid-enriched diet (LD, w/w) on renal function of rats at different ages. Three types of LD were tested: canola oil, fish oil and butter. Mean systemic tail-cuff blood pressure and glycemia remained within the normal range whatever the age and the diet of the animals. Proteinuria began to rise from the 8th month in the groups ingesting LD, while in the control group it increased significantly (above 10 mg/24 h) only after the 10th month. With age, a significant and progressive decline in glomerular filtration rate (GFR) and renal plasma flow was observed in the LD groups but after 6 months of lipid supplementation, the decline in these parameters was more marked in the butter and fish oil groups. By the 18th month, the lowest GFR level was observed in the group ingesting the butter diet (2.93 +/- 0.22 vs 5.01 +/- 0.21 ml min(-1) kg(-1) in control, P<0.05). Net acid excretion, evaluated in 9- and 18-month-old rats, was stimulated in the fish oil group when compared both to control and to the other two LD groups. These results suggest that even low levels of LD in a chronic nutritional regimen can modify the age-related changes in renal function and that the impact of different types of lipid-supplemented diets on renal function depends on the kind of lipid present in the diet.