PROXIMAL REABSORPTION WITH CHANGING TUBULAR FLUID INFLOW IN RAT NEPHRONS

The relative contribution of intraluminal versus peritubular factors i n mediating glomerulo-tubular balance (GTB) is still controversial. We modulated the load of tubular fluid to the proximal tubule of single nephrons of rats by injecting oil into the efferent arteries (EAO). In fifty nephrons the changes in reabsorption induced by obstruction occ urred in the same direction as, and were significantly correlated with , the simultaneous changes in single nephron glomerular filtration rat e (SNGFR) (y = -0.54 + 0.92x, R = 0.91, P < 0.0001). In an additional set of thirty nine nephrons the load of tubular fluid was changed, dur ing EAO, by partial collection from Bowman's space or from the early p roximal convolution. Thus, the rare of tubular fluid delivery along th e proximal tubule was changed in an experimental situation that preven ted any modification in the oncotic pressure of peritubular capillarie s. The changes in proximal deliveries during this experimental conditi on were significantly correlated with those during reabsorption (y = - 2.87 + 0.71x, R = 0.82, P < 0.0001). These data demonstrate that GTB i s fully expressed even when the native peritubular environment is kept constant while the rate of perfusion of proximal tubular segments wit h native tubular fluid is changed.