AJP - Renal Physiology, Vol 248, Issue 1 100-F103, Copyright © 1985 by American Physiological Society
Parathyroid hormone contributes to volume expansion-induced inhibition of proximal reabsorption
O. Mercier, M. Bichara, M. Paillard, J. P. Gardin and F. Leviel
Volume expansion inhibits the proximal reabsorption of water, bicarbonate,
and chloride. The present work tested a hypothetical role of parathyroid
hormone (PTH) in the expansion effect. We studied 19 Sprague-Dawley rats
during a plasma-replete euvolemic state and following 10% body wt
colloid-free expansion. In group I, six intact rats, volume expansion
decreased plasma ionized calcium concentration ([Ca2+]P) from 2.28 +/- 0.06
to 2.11 +/- 0.04 meq/liter and increased nephrogenous cAMP (NcAMP) from 29
+/- 5 to 66 +/- 10 pmol X min-1 X g kidney wt-1. In group II, six acutely
thyroparathyroidectomized (TPTX) rats, [Ca2+]P also fell from 2.18 +/- 0.08
to 1.80 +/- 0.08 meq/liter but NcAMP did not rise significantly (9 +/- 3
vs. 17 +/- 5 pmol X min-1 X g kidney wt-1). These data strongly suggest
that stimulation of PTH activity occurred during expansion in intact
animals. In group III, seven TPTX rats, volume expansion inhibited proximal
reabsorption of total CO2 by 11%, of chloride by 24%, and of water by 19%.
Volume expansion-induced reduction in bicarbonate, chloride, and water
reabsorption was smaller in TPTX than in intact rats previously studied. We
conclude that volume expansion inhibits proximal reabsorption in part by
decreasing the active transcellular NaHCO3 and NaCl transport secondary to
stimulation of PTH activity.
