Abstract
ABSTRACT: The renal phosphate (Pi) transport system matures during the 3rd postnatal wk in the rat by an increase in the carrier affinity for sodium-cotransported phosphate. This study examines the ability of pups to adapt their renal Pi transport to the dietary phosphorus content during this period of carrier affinity maturation, corresponding to the weaning period in the rat. Clearance experiments and brush border membrane studies were performed on 21-d-old rats weaned early on d 16 onto a low phosphate diet (LPD, 0.19 g/100 g), a normal phosphate diet (control, 0.78 g/100 g), or a high phosphate diet (HPD, 1.5 g/100 g). In LPD rats, the Pi fractional excretion (0.3 ± 0.1%) was lower than in controls (18 ± 3%, p < 0.001). It remained very low (0.21 ± 0.05% in LPD rats versus 40.5 ± 6.3% in controls, p < 0.001) after Pi perfusion (1.5 μmol·min-1 · 100 g-1) and the reabsorbed Pi per min, corrected for the glomerular filtration rate, was higher than in the two other groups. The calcium fractional excretion (12.6 ± 1.02%) in the LPD rats was much higher than in the controls (0.42 ± 0.2%, p < 0.001). In contrast, HPD rats had an elevated Pi fractional excretion (41 ± 4%, p < 0.001), whereas reabsorbed phosphate per min corrected for the glomerular filtration rate was not increased by a Pi load. The membrane vesicles from 21-d-old LPD rats had a higher Vmax (11 466 ± 1 840 pmol·mg protein-1·10 s-1) than the controls (7 019 ± 1 112 pmol·mg protein-1·10 s-1, p < 0.01), whereas those from HPD rats had a lower Vmax (5 161 ± 956, p < 0.01). The apparent Km values were unchanged. The LPD rats had high plasma calcium levels. The parathyroid hormone level was depressed by this hypercalcemia [21.97 ± 1.9 pg/mL (2.31 ± 0.2 pmol/L) in LPD and 38.54 ± 2.01 pg/mL (4.05 ± 0.21 pmol/L) in normal Pi diet rats, n = 8, p < 0.001]. This plus their LPD explains the lower Pi fractional excretion of these rats and the low Pi Vmax in their brush border membrane. The plasma parathyroid hormonal level of HPD rats was normal [35.07 ± 2.23 pg/mL (3.69 ± 0.23 pmol/L), n = 8]. We conclude that the young 3-wk-old rat can adapt its renal Pi transport capacity to the dietary phosphorus content during the weaning period by varying the number of functional units of the sodium Pi cotrans-porter or by increasing its turnover rate. Changing the Pi content of the diet induces no apparent change in Pi transport maturation during this period, as there was no change in the carrier affinity.
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Lelievre-Pegorier, M., Leroy, B., Moreau, E. et al. Effects of an Early Weaning on Phosphate Transport Maturation in the Rat Kidney: Influence of the Phosphate Content of the Diet. Pediatr Res 32, 704–709 (1992). https://doi.org/10.1203/00006450-199212000-00017
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DOI: https://doi.org/10.1203/00006450-199212000-00017