Calcium metabolism of intact and thyroparathyroidectomized rats fed a bicarbonate enriched diet.

Rats fed a bicarbonate-enriched diet become alkalotic during their feeding period (ca. 10 h/day). Alkalosis produced a significant reduction in the plasmatic concentration of ionized calcium and increased parathyroid hormone secretion confirmed by concurrent hypophosphatemia and increased urinary excretion of cAMP. Three weeks of treatment produced, however, a significant reduction of bone Ca resorption. The increased endogenous fecal excretion of calcium counteracted the enhancement of true calcium absorption. No significant change in the skeletal calcium mass was observed. Thyroparathyroidectomized rats fed the alkaline diet reduced further their rate of bone Ca resorption and increased significantly their skeletal calcium mass.