The effect of hypocalcemia on renal bicarbonate absorption.

The effect of hypocalcemia on renal bicarbonate absorption (RHCO3/GFR) was examined in bicarbonate-loaded dogs. Following the infusion of ethylene-bis(oxyethylenitrilo)tetraacetic acid (EGTA) in intact dogs, RHCO3/GFR fell from 23.8 +/- 0.7 to 20.8 +/- 0.6 (p less than 0.005) and in thyroparathyroidectomized (TPTX) dogs from 25.6 +/- 1.44 to 23.6 +/- 2.15 (p less than 0.025). By contrast, infusion of EGTA which had been titrated with calcium had no effect, RHCO3/GFR being 27.7 +/- 1.14, control and 28.5 +/- 0.38, during EGTA (p less than 0.05). Hypocalcemia also significantly depressed the renal absorption of phosphate. There were no effects on renal hemodynamics or electrolyte excretion. These studies suggest that plasma-ionized calcium may play a role in regulating renal bicarbonate and phosphate absorption.