Converting enzyme inhibition and glomerular size selectivity in diabetic nephropathy

Differential solute clearances were used to examine the effects of enalapril on glomerular barrier function in 16 proteinuria patients with diabetic glomerulopathy. In these patients, a 90-day course of enalapril reduced arterial pressure without lowering renal plasma flow or glomerular filtration rate. Glomerular clearances of dextrans of broad size distribution (28 to 60 A) were lowered significantly. Theoretical analysis of the dextran clearance profiles revealed that enalapril shifted glomerular pore size distribution to a smaller size. This change in barrier size selectivity was associated with a reduction in fractional albumin and immunoglobulin G clearances during enalapril therapy; urinary protein excretion tended to decrease in parallel. These results indicate that converting enzyme inhibition diminishes glomerular permeability to proteins in diabetic nephropathy by enhancing barrier size selectivity. Because enalapril therapy did not alter the renal plasma flow rate or glomerular filtration rate, these results further suggest that the primary action of enalapril may be to modulate the intrinsic membrane properties of the glomerular barrier.