Relationship between Citrate and Complexed Calcium in Plasma

¹ School of Dentistry, University of North Carolina, Chapel Hill, North Carolina

Hypercalcemia and hypercalcuria consistently occurred in rats fed a low-phosphorus, adequate calcium diet. Measurements of the protein-bound, ionized, and complexed plasma calcium suggested that the excess plasma calcium was distributed among the different portions in a way that the ratio between the fractions and the total plasma calcium remained relatively constant. Alterations in the acid-base balance had the most pronounced effect on the complexed calcium; the ratio between complexed and total calcium was disproportionately high in alkalosis and low in acidosis. Hypercitremia and hypercitruria accompanied the increases in calcium, but only in the alkalotic rats. Most of the elevated plasma citrate combined with calcium to form a calcium citrate complex that accounted for the major portion of the observed rise in complexed calcium in alkalosis.