AJP - Renal Physiology, Vol 251, Issue 5 802-F809, Copyright © 1986 by American Physiological Society
Effects of parathyroid hormone and urinary phosphate on collecting duct hydrogen secretion
O. Mercier, M. Bichara, M. Paillard and A. Prigent
Urine-minus-blood PCO2 (U - B PCO2) during alkaline diuresis (urinary pH
greater than 7.8) was determined in paired experiments using
bicarbonate-loaded rats to assess the effects of parathyroid hormone (PTH)
and urinary phosphate concentration [( Pi]u) on collecting duct H+
secretion. U-B PCO2 was higher for any value of urinary bicarbonate
concentration ([HCO3]u) in the presence of PTH [intact rats and
thyroparathyroidectomized (TPTX) PTH-infused rats] than in its absence
(calcium-infused intact rats and TPTX rats). However, when [Pi]u was
maintained constant by prior phosphate infusion, PTH administration in TPTX
rats failed to elevate U-B PCO2. When PTH was infused in TPTX rats to
maintain constant the plasma PTH level, subsequent phosphate infusion
increased [Pi]u and elevated U-B PCO2 for any value of [HCO3]u. Moreover,
when the data were pooled, there was a positive linear relationship between
U-B PCO2 factored for [HCO3]u and [Pi]u (P less than 0.001). In all
experiments, other factors that may affect U-B PCO2, such as plasma
acid-base status, urinary osmolality, and extracellular fluid volume, did
not vary. We conclude that PTH stimulates collecting duct H+ secretion
indirectly via the increase in [Pi]u.
