Effect of peritubular capillary perfusion rate on proximal sodium reabsorption

Effect of peritubular capillary perfusion rate on proximal sodium reabsorption.The effect of changes in peritubular capillary flow rate on fluid reabsorption by the renal proximal tubule was studied in rats.Absolute and fractional water reabsorption was measured by the recollection technique in end proximal convolutions while the adjacent peritubular capillaries were being microperfused at different rates.Pooled rat plasma with a protein concentration of either 5.3 or 11.6 g/100 ml was used to perfuse the capillary network branching from the efferent arteriole at the center of a vascular "star".Fractional and absolute reabsorption fell consistently when the capillary perfusion rate was raised.This occurred with both the low and high protein solutions.When the capillaries were perfused first at a high rate and then at a lower rate, absolute and fractional reabsorption rose during the second tubular collection, suggesting that the results were not due to an artifact of the recollection method or non-specific effects of capillary perfusion.Although part of the inhibition observed with the low protein solution might have been due to dilution of the normal peritubular capillary proteins (a colloid oncotic effect), the magnitude of inhibition seemed too great to be accounted for by this alone.Furthermore, since inhibition was also found when the hyperoncotic plasma was used to perfuse the capillaries at a high rate, a factor other than colloid oncotic pressure changes seemed evident.The observations are consistent with the view that changes in capillary hydrostatic pressure produced by the different perfusion rates played a role in the changes in sodium and water reabsorption under these experimental conditions. Effet du debit de perfusion capillaire peritubulaire sur la reabsorption proximale du sodium.L'effet des variations du debit capillaire peritubulaire sur la reabsorption du sodium par le tube proximal renal a ete etudie chez des rats.La reabsorption d'eau absolue et fractionnelle a ete mesuree a la fin des tubes proximaux accessibles a differents debits de perfusion des capillaires peritubulaires en utilisant la technique des recollections.Du plasma de rat provenant de pools contenant soit 5,3 soit 11,6 g/100 ml de proteines a ete utilise pour perfuser le reseau capillaire issu d'une arterioleefferente au centre d'une etoile vasculaire.Les reabsorptions fractionelle et absolue ont diminue nettement quand le debit de perfusion capillaire a ete augmente.Cela a ete observe avec les deux concentrations de proteines.Quand les capillaires ont ete perfuses d'abord a un debit eleve puis a un debit plus faible, les reabsorptions absolue et fractionnelle ont augmente au cours de la deuxieme collection, ce qui suggere que les resultats ne sont pas dus a un artifice de la technique de recollection ou a un effet non specifique de la perfusion capillaire.Une partie de l'inhibition observee avec la solution a faible concentration de proteines peut aboir ete liee a la dilution des proteines propres du capillaire peritubulaire (effet colloido-oncotique).Cependant l'importance de l'inhibition semble trop grande pour que ce processus en tende compte exclusivement.De plus, le fait que l'inhibition ait ete obtenue aussi lors de la perfusion du capillaire, a debit eleve, avec du plasma hyperoncotique rend evident l'existence d'un facteur autre que les modifications de pression colloido-oncotique.Ces constatations sont compatibles avec l'idee que les modifications de la pression hydrostatique capillaire produites par les differents debits de perfusion jouent un role dans les modifications de la reabsorption du sodium et de l'eau dans les conditions experimentales utilisees.