Plasma calcium distribution in relation to parathyroid function

¹ Department of Biochemistry, Northwestern University Medical School, Chicago, Illinois

The plasma calcium was fractionated into protein-bound and free fractions by means of an ultracentrifuge in normal, hypoparathyroid and hyperparathyroid dogs and normal and hypoparathyroid rats. The proportion of the total plasma calcium that was diffusible was greater in normal and hypercalcemic animals than in the hypoparathyroid state. Recalcification of hypoparathyroid dog plasma in vitro gave a similar calcium distribution to that obtained when parathyroid extract was injected into hypoparathyroid dogs. Although the binding of calcium per gram of plasma protein increased both in vivo and in vitro as the concentration rose, the results did not conform to the simple mass law relationship as usually expressed. The evidence presented indicates that parathyroid function only influences the distribution of plasma calcium indirectly by regulating its concentration.