EFFECT OF DIETARY-PROTEIN AND ENALAPRIL ON PROXIMAL TUBULAR DELIVERY AND ABSORPTION OF ALBUMIN IN NEPHROTIC RATS

In passive Heymann nephritis (PHN), angiotensin-converting enzyme inhi bition (ACEI) or a low dietary protein intake decreases albuminuria (U A1bV). Although this reduction in albuminuria appears to result from a n improvement in glomerular permselectivity, the effect of these treat ; ments on albumin permeation and absorption by the nephron has not be en clarified. This study used micropuncture techniques to examine the effect of these two treatments on albumin permeation (by measuring the delivery of albumin to the proximal tubule) and the tubular absorptio n of albumin. PHN rats (12-18 days after injection of FX1A) were switc hed from 23% to either 40% protein diet (HP), 40% protein diet and con comitantly treated with enalapril (40 mg . kg(-1). day(-1)) (HPE), or to 8% (LP) protein diet for 4-6 days. Although left kidney glomerular filtration rate (GFR) did not differ among the groups, UA1bV from the left kidney in LP and HPE was only 20-40% of that observed for the HP group. In protocol 1, the fractional recovery of albumin (FR(A1b)) in urine was calculated following injection of artificial tubular fluid c ontaining [C-14]inulin and I-125-labeled albumin into the earliest ide ntifiable proximal loops. There were no differences in FR(A1b) among t he three groups. In protocol 2, timed quantitative collections of tubu lar fluid were obtained from proximal tubular loops. The rate of album in delivery to the earliest accessible loops of the proximal tubule wa s significantly lower for the LP and HPE groups compared with the HP g roup. For each group, albumin concentration corrected for water absorp tion was not altered along the proximal tubule. The data indicate that alterations of dietary protein intake or ACEI treatment results in la rge changes in the delivery of albumin at the proximal tubule that cou ld singularly account for the changes in urinary albumin excretion.