AJP - Renal Physiology, Vol 233, Issue 2 150-F153, Copyright © 1977 by American Physiological Society
Phosphate transport in superficial and deep nephrons in phosphate-loaded rats
F. G. Knox, J. A. Haas, T. Berndt, G. R. Marchand and S. P. Youngberg
We tested the hypothesis that greater phosphate delivery from deep nephrons
than from superficial nephrons contributes to the addition of phosphate to
the collecting system during phosphate loading. In the first group of eight
anesthetized Munich-Wistar rats infused with phosphate and parathyroid
hormone (PTH), fractional delivery of phosphate (FDP%) from superficial
distal tubules was 56 +/- 6%, significantly less than the amount appearing
in the urine, 67 +/- 6% (P less than 0.01). In the second group of six
rats, we determined whether this addition of phosphate could be accounted
for by a higher FDP% from the deep nephrons. Free-flow micropuncture
collections were taken from deep nephrons (ascending limb of the loop of
Henle in the papilla), superficial nephrons (distal tubules in the cortex),
and urine (duct of Bellini). The FDP% to the ascending limb of the loop of
Henle in deep nephrons was 78 +/- 10%, significantly greater than to the
distal convoluted tubules in superficial nephrons, 51 +/- 6% (P less than
0.005), and the fractional excretion of phosphate in urine, 72 +/- 10% (P
less than 0.05). Although a difference between FDP% in superficial and deep
nephrons due to reabsorption in the ascending limb of the loop of Henle
cannot be ruled out from the present data, other studies indicate that this
interpretation is unlikely. We conclude that greater phosphate delivery by
deep nephrons contributes to the addition of phosphate to the collecting
system of phosphate-loaded rats.
