Effects of saline infusion on glomerulotubular balance

Effects of saline infusion on glomerulotubular balance.The purpose of this study was to determine the relative contributions of superficial nephron filtration rate (NFR) and the absolute rates of proximal tubular reabsorption to the maintenance of relatively constant fractional reabsorption when kidney glomerular filtration rate (GFR) is decreased experimentally, and the extent to which glomerulotubular balance occurs in the presence of saline infusion which decreases fractional reabsorption in the proximal tubule.NFR and proximal tubular fractional reabsorption were measured by collection and recollection of total tubular fluid, before and after reducing kidney GFR in hydropenic rats.These measurements were repeated for a different group of nephrons in the same animals after saline infusion.Glomerulotubular balance, expressed as constancy of fractional reabsorption when kidney GFR was decreased by aortic constriction, was 88% complete in hydropenic animals, but only 36% complete after saline infusion.On the average, NFR and kidney GFR decreased proportionately during aortic constriction (-54% and -50%, respectively, during hydropenia and -52% and -47% during saline infusion).Therefore, the high degree of glomerulotubular balance in hydropenic animals was accounted for almost entirely by a fall in calculated absolute reabsorptive rate, which paralleled the fall in NFR and kidney GFR.Less complete glomerulotubular balance during saline infusion was due to failure of calculated reabsorptive rates to decrease in near proportion to the decreases in NFR and kidney GFR.Saline infusion alone decreased absolute reabsorption an average of 48% and this may have precluded or blunted any further decrease during aortic constriction.The data indicate: 1) proportionality between changes in NFR and kidney GFR after saline infusion and during aortic constriction in the absence and presence of saline infusion, 2) near proportionality between changes in NFR and absolute proximal tubular reabsorptive rate during aortic constriction in hydropenic rats but not in saline loaded rats, 3) saline infusion depresses the absolute rate of proximal tubular reabsorption and this accounts largely for the fall in fractional reabsorption, and 4) reduced glomerulotubular balance during aortic constriction after saline infusion due to a limitation in further downward adjustment of absolute reabsorption as NFR is reduced. Effet de la perfusion de solution saline sur la balance glomerulotubulaire.Le but de cette etude etait de determiner les contributions relatives du taux de filtration par les nephrons superficiels (NFR) et des taux absolus de reabsorption tubulaire proximale au maintien d'une reabsorption fractionelle relativement constante lorsque la filtration glomerulaire (GFR) du rein est diminuee de facon experimentale, et dans quelle mesure on peut obtenir l'equilibre quand une perfusion de solution saline diminue la reabsorption fractionelle dans le tubule proximal.NFR et la reabsorptionnelle tubulaire proximale ont ete mesures par collection et recollection de la totalite du liquide tubulaire chez des rats hydropeniques avant at apres diminution de la GFR du rein.Ces mesures ont ete repetees pour un groupe different de nephrons, chez le meme animal, apres perfusion de solution saline.L'equilibre glomerulotubulaire, exprime par la constante de la reabsorption fractionnelle lorsque la GFR du rein est diminuee par constriction aortique, se trouvait maintenu a 88% chez les rats hydropeniques, mais ne l'est plus qu'a 36% apres perfusion de solution saline.En moyenne, la NFR et la GFR du rein avarent diminue de facon proportionnelle au cours de la constriction aortique (-54% et -50%) respectivement durant l'hydropenie et -52% et -47% durant la perfusion de solution saline.Le degre eleve d'equilibre glomerulotubulaire chez les animaux hydropeniques est donc attribue en majeure partie a une diminution du taux absolu de reabsorption (calcule), lequel varie de facon parallele avec la diminution de la NFR et de la GFR du rein.La deficience de l'equilibre glomerulotubulaire au cours de la perfusion de solution saline est due au fait que les taux (calcules) reabsorption ne diminuent pas proportionnellement au NFR et a la GFR due rein.Pas elle meme, la perfusion de solution saline provoque une diminution moyenne de 48% de la reabsorption absolue et ceci peut avoir empeche ou minimise toute diminution subsequente au cours de la constriction aortique.Les resultats indiquent: 1) la proportionnalite des variations du NFR et de la GFR due rein apres perfusion de solution saline et au cours de la constriction aortique en presence ou non de perfusion de solution saline, 2) la presque proportionnalite des variations du NFR et du taux de reabsorption tubulaire proximale absolue au cours de la constriction aortique chez les rats hydropeniques mais non chez des rats surcharges en sel, 3) la perfusion de solution saline diminue le taux absolu de reabsorption tubulaire proximale, ce qui explique en grande partie la diminution de la reabsorption fractionnelle, 4) la diminution de l'equilibre glomerulotubulaire au cours de la constriction aortique apres perfusion de solution saline, du fait de l'impossibilite de diminuer davantage la reabsorption absolue pendant la reduction du NFR.