Effective hydraulic permeability of the glomerular capillary wall in rats after uninephrectomy.

The effective hydraulic permeability (k) of glomerular capillaries was studied in 2-month-old Wistar rats 4 weeks after uninephrectomy in comparison to age-matched control rats. Isolated kidneys were perfused with a cell-free solution containing 5% albumin. In this preparation the rise of colloid osmotic pressure along the glomerular capillaries can be neglected because the filtration fraction is low (3%) due to high perfusion rates at normal filtration rates. Single nephron filtration rates (SNGFR) and effective filtration pressures were estimated by micropuncture to calculate the ultrafiltration coefficient (Kf). Glomerular capillary surface area was measured morphometrically to obtain k (k = Kf/S). We found that the effective hydraulic permeability in uninephrectomized rats was higher than in rats of comparable age (26.0 vs 18.0 nl/mm Hg X s X cm2). This can contribute to the adaptive rise in SNGFR after uninephrectomy.