GLOMERULAR HEMODYNAMICS IN RATS WITH CHRONIC SODIUM DEPLETION - EFFECT OF SARALASIN

In chronic sodium depletion the glomerular filtration rate may be reduced, and alterations in proximal tubular function may contribute to the maintenance of antinatriuresis. Measurements were made by micropuncture technique in superficial nephrons of the Munich-Wistar rat of the determinants of glomerular filtration rate, peritubular capillary hydrostatic and oncotic pressure, and proximal tubular fractional and absolute reabsorption in both a control group (group 1, n=12) and a group of chronically sodium-depleted rats (group 2, n=12). Single nephron filtration rate (sngfr) was 37.2 ± 1.2 in group 1 and 31.6 ± 1.0 nl/min/g kidney wt (P<0.05) in group 2. Of the factors potentially responsible for the observed reduction in sngfr, there was no change in systemic oncotic pressure or the transglomerular hydrostatic pressure gradient. Sngfr was lower in group 2 because of both a reduced single nephron plasma flow (rpf) (128 ± 6 vs. 112 ±5 nl/min per g kidney wt, P<0.05) and additionally to a decrease in the glomerular permeability coefficient, L(p)A, from a minimum value of 0.105 ± 0.012 in group 1 to 0.054 ±0.01 nl/s per g kidney wt per mm Hg (P<0.01) after chronic sodium depletion. There was no difference in fractional proximal tubular reabsorption between group 1 and group 2. Absolute proximal reabsorption (APR) was reduced from 20.8±1.3 in group 1 to 16.3±0.9 nl/min per g kidney wt in group 2.