Ultrafiltration coefficient of isolated glomeruli of rats aged 4 days to maturation.

In the developing rat, RBF and GFR increase in parallel. We have calculated filtration coefficient (Kf) and hydraulic conductivity (Lp) of the glomerular capillary using glomeruli isolated from Munich-Wistar rats aged 4 days to adult. Lp derived as the quotient of Kf and total basement membrane area (LpS) may represent a minimum estimate, while the quotient of Kf and the peripheral basement membrane area (LpP) may more accurately represent the value that is operative in vivo. Rats in Group 1 (age 4 to 9 days) had an average glomerular diameter of 87 +/- 3 microns, Kf of 1.7 +/- 0.3 nl/min . mm Hg and LpS and LpP, 1.9 +/- 0.2 and 4.4 +/- 0.6 microliter/min . mm Hg . cm2, respectively. Glomerular diameter and Kf were not significantly increased in rats of Group 2 (22 to 36 days), but LpS and LpP diminished to 1.5 +/- 0.1 and 2.6 +/- 0.2 microliter/min . mm Hg . cm2 because of an increase in basement membrane surface density. In older rats of Groups 3 (69 to 84 days) and 4 (about 120 days, wt 205 +/- 4 g), glomerular diameter and Kf increased progressively. Kf and diameter were greater in deep than in superficial glomeruli of Group 4. In superficial glomeruli of Group 4, LpS averaged 1.1 +/- 0.1 and LpP 2.0 +/- 0.1 microliter/min . mm Hg . cm2, and were significantly lower than the values for Group 2 but not different from those of deep glomeruli of Group 4. Relative erythrocyte ejection increased with increasing glomerular diameter, indicating decreasing capillary resistance. Our observations at consistent with the previous reports that renal perfusion, Kf, and filtration rate increase in parallel, but do not support the hypothesis that glomerular capillary hydraulic conductivity increases as the filtration barrier matures.