Correlation between single nephron glomerular filtration rate and filtration area in superficial glomeruli of developing rats.

Single nephron glomerular filtration rate (SNGFR) was correlated to the area of the glomerular basement membrane (GBM) determined by stereological techniques in rats between 20 and 40 days of age. Single nephron glomerular filtration rate increased 8.4 times in parallel with a twofold increase in GBM area. The much greater postnatal increase in SNGFR than in GBM area demonstrates that the increase in GBM area cannot account for the entire increase in SNGFR. Instead a combination of other factors influencing SNGFR most likely determines the largest part of the increase in SNGFR during this period. Thus, the drop in vascular resistance known to occur during maturation will increase the renal blood flow and may cause the filtration process to turn from a state of filtration equilibrium to or close to disequilibrium, thereby increasing GFR. Additional increase in GFR may be due to an increased net driving force for filtration and/or changed hydraulic permeability.