Renal brush border membrane adaptation to phosphorus deprivation: Effects of fasting versus low-phosphorus diet

Renal brush border membrane adaptation to phosphorus deprivation: Effects of fasting versus low-phosphorus diet. limentary phosphorus deprivation due to a low-phosphorus diet (LPD) elicits a profound antiphosphaturia and an increase in sodium-dependent inorganic phosphate (Pi) uptake by renal cortical brush border membrane (BBM) vesicles. But, in alimentary phosphorus deprivation due to total fasting, high urinary excretion of Pi persists. In the present study, we determined whether low tubular reabsorption of Pi in fasting is due to a diminished capacity of the specific Pi transport system with the renal cortical luminal BBM or whether it is due to a reduced transepithelial reabsorption of Pi because of metabolic conditions occurring in proximal tubule cells during fasting. Sodium-dependent Pi transport in BBM vesicles isolated from LPD rats was markedly increased compared with fasted rats or rats fed a normal phosphorus diet. Sodium-dependent uptake of D-glucose was significantly lower in LPD rats, compared with fasted animals or animals fed a normal diet. Thus, in contrast to LPD, fasting does not elicit an increase in Pi transport and a decrease in D-glucose transport across the isolated renal BBM. The same differences in BBM transport of Pi were present also in thyroparathyroidectomized rats. Further experiments demonstrated that the adaptation of renal function and the renal BBM transport to LPD are overridden by a subsequent period of total fasting. Results of the present study show that fasting both prevents and reverses the renal response of rats to alimentary phosphorus deprivation. The differences in Pi excretion between fasted rats, LPD rats, and LPD rats subsequently fasted are attributed, at least in part, to specific adaptive changes in sodium-dependent Pi transport across the luminal BBM, rather than to alterations in other cellular (metabolic) components of transepithelial Pi reabsorption in the proximal tubule. Adaptation de la bordure en brosse rénale à la privation de phosphore: Effets du jeûne comparé à une alimentation pauvre en phosphore. La privation de phosphore alimentaire, obtenue au moyen d'une alimentation pauvre en phosphore (LPD), détermine une chute importante de la phosphaturie et une augmentation de la captation sodium-dépendante de phosphore (Pi) par les vésicules de la membrane de bordure en brosse (BBM). Dans la privation alimentaire de phosphore due au jeûne total, cependant, une excrétion urinaire élevée de phosphore