The Influence of the Protein Level of the Diet on Serum Glycoprotein Concentrations in the Rat

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Abstract
The influence of the protein level of the diet on the concentration and distribution of the serum glycoproteins has been investigated by the rat depletion-repletion method. Male rats weighing approximately 400 gm were fed a protein-free diet until they had lost 25% of their weight. They were then repleted with isocaloric diets containing 8, 17, 27, 40, and 64% of casein. When their original weight was regained, the animals were exsanguinated. The protein-bound carbohydrates and proteins of whole serum, and of the seromucoid, albumin, and globulin fractions, and the hemoglobin and hematocrit values of blood were determined. Following depletion, significant decreases occurred in all serum constituents with the exception of the protein-bound carbohydrate of the albumin fraction. Diets containing 17% or more of casein were adequate to restore total glycoprotein and globulin polysaccharide levels to their normal range. Subnormal values for the polysaccharide components of the seromucoid and albumin fractions occurred on repletion diets. With the exception of the 8% level of casein, all other repletion diets were not only adequate for the restoration of the total serum proteins but elicited marked increases due to the elevation of the serum globulins. The differential response of the protein-bound carbohydrates and proteins of the seromucoid and globulin fractions resulted in decreased polysaccharide-protein ratios for the fractions in all repleted groups.