Effect of Vitamin D on Tissue Distribution and Transport of Electrolytes,47Ca and28Mg

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Abstract
The administration of 100,000 to 200,000 units of calciferol to adult dogs daily for 5 wk. caused marked hypercalcemia and significant decreases in plasma concentrations of Na, K, Mg and Cl-. Cellular concentrations of Ca were increased by 30 to 300% in muscle, myocardium, pancreas and aorta andwere unchanged in liver, brain and nerve. Bone uptake of Ca47was increasedby 45%. The exchangeable body and tissue pools of Cawere increasedby 100% but the fractional rate of exchange of tissue Ca was unaltered. The Mg concentrations of liver, pancreas and bone were increased by 16 to 20% by calciferol and the fractional rate of exchange of tissue Mg with Mg28 was increased by 23%. Calciferol administration had a minor effect on tissue concentrations of acid-soluble phosphorus. The Na concentrations of 5 tissues and the Cl- concentrations of 3 tissues were significantly decreased, whereas the K concentrations of 2 tissues were increased significantly. These data support the hypothesis that vitamin D, like parathyroid hormone, stimulates the cellular transport of Ca and Mg. However, the different quantitative effects of these agents on the distribution and transport of divalent cations and the inability of vitamin D, in contradistinction to parathyroid hormone, to influence the tissue concentrations of P and of univalent electrolytes which are usually present in hypercalcemia suggest that different loci and/or modes of action are involved in the effects of vitamin D and parathyroid hormone on cellular transport processes.

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