Nephron heterogeneity of phosphate reabsorption

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.