Studies in calcium metabolism

Abstract

Quantitative analyses were done on true plasma, citrated plasma, serum, and corpuscles, and a study of the physical state of Ca in serum and plasma was made. The animals were cats, anesthetized by paraldehyde and ether. Kramer and Tisdall''s method was used. It was found that the Ca content of true plasma is 10-20% greater than that of the corresponding serum. The Ca of citrated centrifuged plasma is roughly equal to that of the corresponding serum. The corpuscles contain only a trace of Ca. Ionic Ca was determined by the Brinkman and Van Dam method. Some 80% of the serum Ca is present in combination, part with simple inorganic radicles such as phosphate and bicarbonate, and part possibly with protein. In measuring diffusible Ca the collodion filtration method was used. The peritoneum of the cat was used as a semi-permeable membrane, the diffusion being carried out in vivo, in the anesthetized animal, and the findings compared with those in the ultrafiltrate of the corresponding serum. Diffusion between the fluid in the peritoneal cavity and the circulating blood was allowed to go on for 2-6 hrs. In all cases a Ca-containing fluid, in which the Ca concentration equaled that of the diffusible Ca of the serum, was recovered from the peritoneal cavity, irrespective of the Ca in the original fluid. The curve of diffusion definitely tends to reach a constant level. The authors conclude that a fraction of the Ca present in the plasma exists as a non-colloidal diffusible complex partly in the ionized state, and that this diffusible complex and also the ionized Ca is equal in amount to that in the corresponding serum. Conversely, the results suggest that the distribution of Ca in the serum between crystalloid and colloid as determined by collodion ultrafiltration is quantitatively comparable with that in plasma. It appears that some Ca is withdrawn from the plasma during clotting. Since the findings suggest that the amount of diffusible and ionized Ca in the plasma is equal to that of the serum, it seems probable that it is the non-diffusible complex which is involved.