Calcium-binding protein and vitamin D metabolism in experimental protein malnutrition

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Abstract
1. Intestinal and renal vitamin D-dependent calcium-binding protein (CaBP) activity and cholecalciferol metabolism were investigated in the protein-deficient rat (40 g casein/kg diet) and in control animals (200 g casein/kg diet). Compared to control animals, 3 weeks of protein deprivation resulted in consistently reduced intestinal CaBP activity, while renal CaBP activity was not significantly altered.2. Intestinal CaBP activity was greatly reduced in rats fed on diets deficient in both protein and vitamin D. CaBP activity was doubled by cholecalciferol administration, but did not reach control values. The rate of conversion of intravenously injected [3H]cholecalciferol to 25-hydroxycholecalciferol (25-HCC) and the disappearance rates of plasma 25-HCC were similar in the two groups of animals.3. It is concluded that in the protein-deficient rat: (a) intestinal CaBP activity is reduced; (b) coexistent vitamin D deficiency reduces intestinal CaBP activity still further, but the intestinal mucosa retains the potential to respond to administered cholecalciferol: (c) hepatic and probably renal metabolism of cholecalciferol appear to be normal; (d) reduced CaBP is likely to be the result of reduced CaBP synthesis as a consequence of deficient amino acid substrate.