Effects of nephrectomy and high-protein diets on glomerular hemodynamics and urinary protein excretion in diabetic rats

Renal blood flow, GFR, albumin clearance, and urinary excretion of proteins were assessed in intact control and streptozotocin-diabetic rats (group 1), unilaterally nephrectomized control and diabetic rats (group 2), and nephrectomized control and diabetic rats (divided into high (a) and low (b) glycemia subgroups) fed a 50% protein diet (group 3). After 8 months of diabetes, blood flow did not differ from control rats within each experimental group, although it was increased significantly in both controls and diabetics of groups 2 and 3 versus group 1. GFR in control rats was increased ∼2x by nephrectomy and ∼3x by nephrectomy plus the high protein diet. Diabetes increased GFR ∼50% above control values in group 1; GFR values in diabetic rats of groups 2 and 3a were virtually identical and similar to those of group 2 controls; GFR in group 3b diabetics was increased ∼1.4x versus group 2 diabetics. ¹²⁵I-BSA clearance was increased 3.4x in groups 2 and 3 control rats versus group 1 controls. Both nephrectomy and consumption of the high protein diet caused marked increases in ¹²⁵I-BSA clearance and urinary excretion of albumin in diabetic rats. Urinary excretion of IgG was increased by diabetes in group 1 and remained essentially at this level in groups 2 and 3 diabetic rats. These results demonstrate: 1) additive effects of nephrectomy and increased protein consumption on renal blood flow, GFR, and urinary excretion of albumin and IgG in nondiabetic rats, but only on albumin clearance and excretion in diabetic rats; and 2) consumption of a protein rich diet by nephrectomized diabetic rats was associated with substantial increases in renal blood flow and GFR and with a doubling of albumin clearance and albuminuria despite a substantial amelioration of the diabetic state.