Effects of an early weaning on phosphate transport maturation in the rat kidney: influence of the phosphate content of the diet.

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 mumol.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.(ABSTRACT TRUNCATED AT 250 WORDS)