Phosphopeptides and soluble calcium in the small intestine of rats given a casein diet

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Abstract
1. Semi-synthetic diets containing 200 g protein/kg were meal-fed for 1.5 h to groups of rats. The contents of the whole small intestinal tract were collected and the amount of soluble calcium was determined. 2. In the rats given 200 g casein/kg diet, formation of a fraction containing macrophosphopeptide in the small intestine was confirmed by gelfiltration of the intestinal contents on Sephadex G-25. However, this macrophosphopeptide fraction was not found when casein alone was fed. 3. In the intestinal contents at 2.5 h after ingestion, the amounts of both soluble Ca and phosphorus were significantly higher in rats fed the casein diet than in those fed diets containing egg albumin, isolated soyabean protein or an amino acid mixture. However, the amount of insoluble Ca was least in rats fed the casein diet.