Parathyroid hormone-independent adaptation of the renal handling of phosphate in response to renal mass reduction.
In man as well as in experimental animals progressive renal failure is associated with a decrease in the fractional reabsorption (FR) of inorganic phosphate (Pi). This response has been considered as an adaptation phenomenon and generally attributed to an increase in parathyroid hormone (PTH) secretion. One report indicates that in chronic thyroparathyroidectomized (TPTX) dogs treated with large doses of vitamin D progressive renal failure can also be associated with a fall in FRPi. However, in this latter study the concomittant administration of vitamin D could have accounted for the observed decrease in FRPi. In our study we investigated whether or not chronic reduction in renal mass leads to a similar decrease in maximal net tubular Pi reabsorption per volume of glomerular filtrate (maximal TRPi/ml GF) in the presence and absence of PTH and without pharmacological supplementation in vitamin D. Male rats were either TPTX or sham-operated (intact). One and two weeks later the animals of both groups were either subtotally nephrectomized (NX) in two stages or sham-operated (control). Four weeks after the second renal operation, the glomerular filtration rate (GFR) and the reabsorption of Pi were determined by clearance methodology under acute sodium chloride and Pi infusion, that is, at endogenous and increased plasma Pi concentrations ([Pi]Pl.). Thus maximal TRPi/ml GFR could be determined. In rats with intact parathyroid glands GFR was 1.56 +/- 0.10 (mean +/- SEM) and 0.54 +/- 0.10 ml/min in control and NX respectively, whereas maximal TRPi/ml GF was 2.24 +/- 0.07 in control and 1.57 +/- 0.18 mumol/ml (P less than 0.005) in NX. In TPTX rats GFR was 1.66 +/- 0.27 and 0.62 +/- 0.06 ml/min in control and NX respectively, whereas maximal TRPi/ml GF was 3.80 +/- 0.20 in control and 2.95 +/- 0.13 mumol/ml (P less than 0.005) in NX. The marked decrease in maximal TRPi/ml GF observed in TPTX after subtotal NX could not be ascribed to any consistent change in plasma calcium. Our study provides conclusive evidence that the decrease in maximal TRPi/ml GF in response to renal mass reduction can occur to the same degree in the presence or absence of PTH.
D000222:Adaptation, Physiological; D000818:Animals; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000502:physiology*; D008297:Male; D009392:Nephrectomy; D010280:Parathyroid Glands / Q000601:surgery; D010281:Parathyroid Hormone / Q000502:physiology*; D010710:Phosphates / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013961:Thyroid Gland / Q000601:surgery
D010281:Parathyroid Hormone; D010710:Phosphates