Renal phosphate reabsorption in the rat: effect of inhibitors

The maximum rate of inorganic phosphorus (P1) reabsorption (Tmp1) was measured during phosphate infusion in chronically parathyroidectomized rats. In either initially hydropenic rats or others which underwent moderate preliminary saline loading, Tmp1 tended to rise during early phosphate infusion and then decline, so that steady-state Tmp1 values were similar to the P1 reabsorption rates at the animals' own evelated endogenous plasma P1 concentrations. These results indicate that the "self-depression" of Tmp1 during phosphate infusion is not dependent upon the progressive stimulation of endogenous parathyroid hormone secretion. Parathyroid hormone and dibutyryl cyclic adenosine monophosphate (AMP) decreased Tmp1 substantially, whereas acetazolamide inhibited P1 reabsorption at lower filtered P1 loads but did not diminish Tmp1.