Bicarbonate reabsorption in experimental renal disease: Effects of proportional reduction of sodium or phosphate intake

Schmidt, R. William; Gavellas, George
December 1977
Kidney International;Dec1977, Vol. 12 Issue 6, p393
Academic Journal
In the dog with an experimental form of advanced renal disease, bicarbonate reabsorption per unit of GFR has been reported to be increased in comparison to the rates of reabsorption obtained in normal dogs. The increase occurs despite high fractional excretory rates for phosphate and for sodium factors which could be expected to be associated with decreased bicarbonate reabsorptive capacity. The present study examines the effect of "proportional reduction" of the intake of either phosphate or sodium on the ability of the dog with experimental renal disease to reabsorb bicarbonate during bicarbonate titration experiments. In the control group receiving a constant diet, GFR was reduced to 15.0 ml/min. The fractional excretion of sodium (FENa) rose to 1.42%, and the fractional excretion of phosphorus (FEp) rose to 32.37%. In a second group, GFR was decreased to 18.0 ml/min, and FENa rose to 1.32%, but FEp remained at a low level as the result of proportional reduction of phosphate intake. The bicarbonate reabsorptive capacity was increased significantly in this latter group in comparison to the control group. In a third group. GFR was decreased to 16.9 ml/min and FHp rose to 24.96%, but FENa remained at a low level as the result of a proportional reduction of sodium intake. In this group, bicarbonate reabsorptive capacity was reduced markedly in comparison to the control group and did not appear to be different from the reabsorptive capacity reported previously in normal dogs. At all comparable levels of fractional excretion of chloride (FECl). bicarbonate reabsorption was increased in group II compared to control and reduced in group III compared to control. The ratio of absolute bicarbonate reabsorption lo absolute sodium reabsorption was examined at multiple points as plasma bicarbonate was increased. At all concentrations of plasma bicarbonate, the ratio was higher in group II and lower in group I than in controls. At all levels of sodium balance during the study, bicarbonate reabsorption was increased in group II and reduced in group III compared to control. A fourth group received a high chloride diet. No correlation between dietary chloride intake and bicarbonate reabsorption was demonstrated. The data demonstrate that proportional reduction of phosphate intake in the dog with experimental renal disease allows for an enhancement of the capacity to reabsorb bicarbonate. Proportional reduction of sodium intake in the dog with experimental renal disease is associated with a decreased capacity to reabsorb bicarbonate. These effects do not appear to be related to the status of the extracellular fluid volume, to differences in plasma carbon dioxide tension, or to differences in plasma potassium.


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