AJP - Renal Physiology, Vol 248, Issue 2 175-F182, Copyright © 1985 by American Physiological Society
Phosphate excretion in uremic rats: effects of parathyroidectomy and phosphate restriction
E. Kraus, G. Briefel, L. Cheng, B. Sacktor and D. Spector
As progressive renal failure develops, phosphate excretion per functioning
nephron increases, thus preserving homeostasis. To test whether dietary
phosphate supply might contribute to the regulation of renal phosphate
excretion in the uremic setting, groups of male Sprague-Dawley rats that
were either parathyroidectomized (PTX) or sham PTX (S-PTX) and either
five-sixths nephrectomized (Nx) or sham Nx (S-Nx) were studied following a
4-wk dietary regimen consisting of 0.1 or 0.7% phosphate. For Nx rats fed
the 0.7% phosphate diet the fractional excretion of phosphate (FEPi) was
enhanced (47 +/- 6 vs. 21 +/- 3%) and the maximum tubular reabsorption of
phosphate per milliliter GFR (TmPi/GFR) was suppressed (1.65 +/- 0.19 vs.
2.33 +/- 0.19 mumol/ml). FEPi was unchanged by PTX in these Nx animals (42
+/- 6 vs. 47 +/- 6%). TmPi/GFR remained suppressed in PTX, NX animals when
compared with S-Nx, PTX controls (3.38 +/- 0.33 vs. 5.07 +/- 0.41
mumol/ml). For rats fed the 0.1% phosphate diet Nx did not affect TmPi/GFR
in either S-PTX (5.40 +/- 0.43 vs. 4.97 +/- 0.34 mumol/ml) or PTX (7.03 +/-
0.23 vs. 6.98 +/- 0.21 mumol/ml) animals. For both S-Nx and Nx animals the
effects of PTX and dietary phosphate restriction on TmPi/GFR were
independent and additive. In all groups of animals, tubular reabsorption of
phosphate per milliliter GFR (TRPi/GFR) dropped acutely with continued
infusion of phosphate once TmPi/GFR was achieved. Thus, a resetting of
TRPi/GFR occurs among Nx rats in response to both chronic dietary phosphate
deprivation and acute intravenous phosphate loading.(ABSTRACT TRUNCATED AT
250 WORDS)
