Phosphate reabsorption in the kidney: NaPi-IIb or not IIb

Previous micropuncture studies in rats have demonstrated that fractional phosphate delivery (FDP%) from superficial distal nephrons is higher than in urine. To determine whether this apparent reabsorption could be accounted for by a lower FDP% from the deep nephrons, FDP% was determined in free-low micropuncture from deep nephrons (DN) (ascending limb of the loop of Henle in the papilla), superficial nephrons (SN) (distal tubules in the cortex), and urine (duct of Bellini). In six acute thyroparathyroidectomized (TPTX) rats, FDP% in DN was significantly less than SN. The urinary fractional phosphate excretion (FEP%) was significantly less than in the SN, but not significantly different from the DN. In six chronic TPTX rats, FDP% in DN was significantly less than in SN. The urinary FEP% was significantly less than the FDP% in the SN, and significantly less than the FDP% in the DN, evidence which favors phosphate reabsorption in the terminal nephron. We conclude that in TPTX rats, which are conserving phosphate, deep nephrons reabsorb phosphate more avidly than superficial nephrons.

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Nephron heterogeneity of phosphate reabsorption: effect of parathyroid hormone

AJP Renal Physiology ◽

10.1152/ajprenal.1984.246.2.f155 ◽

1984 ◽

Vol 246 (2) ◽

pp. F155-F158

Author(s):

A. Haramati ◽

J. A. Haas ◽

F. G. Knox

Keyword(s):

Parathyroid Hormone ◽

Proximal Tubule ◽

Distal Tubule ◽

Proximal Tubules ◽

Loop Of Henle ◽

Phosphate Reabsorption ◽

Phosphate Excretion ◽

Before And After ◽

Superficial And Deep Nephrons ◽

Nephron Heterogeneity

We evaluated the response of superficial and deep nephron proximal tubules to PTH in thyroparathyroidectomized (TPTX) rats fed a normal phosphate diet (0.7%). As phosphate reabsorption is not detectable in the ascending limb of the loop of Henle, fractional phosphate delivery (FDPi%) to the superficial early distal tubule and papillary loop of Henle reflects delivery from superficial and deep nephron proximal tubules, respectively. Re-collection micropuncture experiments were performed in nine acutely TPTX rats before and after the infusion of PTH (33 U/kg bolus; 1 U X kg-1 X min-1). In response to PTH, fractional phosphate excretion increased from 3.3 to 26.2% (P less than 0.05). FDPi% was less from the deep than from the superficial proximal tubule (5.7 vs. 15.7%, P less than 0.05) prior to PTH, indicating enhanced phosphate reabsorption by deep compared with superficial proximal tubules. During PTH infusion, FDPi% was increased in both nephron groups compared with control (P less than 0.05), but there were no differences in phosphate delivery between deep (28.0%) and superficial (29.7%) proximal tubules. We conclude that in acutely volume-expanded TPTX rats, infusion of a pharmacologic dose of PTH decreases phosphate reabsorption in both superficial and deep nephrons. Furthermore, the heterogeneity of FDPi% from deep compared with superficial proximal tubules seen in TPTX rats is absent during PTH infusion.

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