AJP - Renal Physiology, Vol 249, Issue 6 912-F918, Copyright © 1985 by American Physiological Society
Extrarenal handling of phosphate: effect of thyroparathyroidectomy, 1,25-dihydroxycholecalciferol, and dietary calcium
U. Troehler, J. P. Bonjour and H. Fleisch
It is known that 1,25-dihydroxycholecalciferol [1,25(OH)2D3] mobilizes
inorganic phosphate (Pi) from gut and bone, thus increasing the entry of Pi
into the extracellular space (ECS). In this work, we have investigated
whether 1,25(OH)2D3 could also facilitate the net exit of Pi out of this
pool into certain soft tissue and/or bone compartments in
thyroparathyroidectomized (TPTX) rats. Sham-operated, TPTX, and TPTX rats
treated with 1,25(OH)2D3 (26 pmol/day ip for 1 wk) were infused with a
known amount of Pi over a given time. The amount of Pi excreted in the
urine in excess of base-line values and the rise of the phosphatemia
([Pi]p) were measured. The difference between these two parameters
corresponded to the net retention of infused Pi in the whole animal (RAPi)
for a given rise in [Pi]p. The results show that RAPi was markedly
diminished in TPTX as compared with sham-operated animals. This decrease
could be corrected by 1,25(OH)2D3 treatment. Chronic reduction in the level
of calcemia in TPTX 1,25(OH)2D3-supplemented rats as induced by decreasing
dietary Ca intake also diminished RAPi. These effects could not be ascribed
to the known actions of the experimental maneuvers on the renal excretion
of Pi. Since infusions were chosen to obtain similar rises in [Pi]p and
started from same levels of [Pi]p in animals of the same weight, the
differences in RAPi were not due to variation of Pi retention in the
ECS.(ABSTRACT TRUNCATED AT 250 WORDS)
