AJP - Renal Physiology, Vol 258, Issue 6 1650-F1656, Copyright © 1990 by American Physiological Society
Renal adaptation to changes in dietary phosphate during development
S. E. Mulroney and A. Haramati
Department of Physiology and Biophysics, Georgetown University School of Medicine, Washington, DC 20007.
The present study tested the hypothesis that the influence of dietary
phosphate (Pi) on the renal handling of Pi changes during development. We
evaluated whether variations in the dietary Pi content would alter the
tubular capacity of Pi reabsorption [Max RPi/glomerular filtration rate
(GFR)] in immature rats, which have a relatively greater Max RPi/GFR
compared with adult rats. Then we examined the response of immature and
adult Pi-deprived rats to dietary Pi replenishment. Studies were performed
in acutely thyroparathyroidectomized Wistar rats at three different stages
of development: immature (3- to 4-wk old), young (6- to 7-wk old), and
adult (12- to 13-wk old). Animals were fed either low (0.07%)-, normal
(0.7%), or high (1.8%)-phosphate diet (LPD, NPD, and HPD, respectively) for
4 days and were then prepared for renal clearance experiments to determine
the Max RPi/GFR. On all dietary regimens, the Max RPi/GFR was highest in
immature rats and decreased progressively with age. When fed LPD, immature
rats, with an already elevated rate of phosphate transport, displayed a
remarkable 68 +/- 13% increase in the Max RPi/GFR (from 5.58 +/- 0.29 to
9.47 +/- 0.76 mumol/ml, P less than 0.01). This was significantly greater
than the 38 +/- 3% increase observed in adult rats (from 3.50 +/- 0.18 to
4.81 +/- 0.09 mumol/ml). Conversely, in response to HPD, the decrease in
the Max RPi/GFR was smallest in immature rats (-42 +/- 2%) compared with
the decrement in either young (-54 +/- 3%) or adult (-61 +/- 6%)
rats.(ABSTRACT TRUNCATED AT 250 WORDS)
