When blood plasma proteins are depleted by bleeding with return of the washed red blood cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a uniform plasma protein production on a basal low protein diet. These dogs are clinically normal. By the introduction of variables into their standardized existence insight into the formation of plasma proteins can be obtained. The liver basal diet maintains health in such hypoproteinemic dogs during periods as long as a year. 17 to 27 per cent of its protein content (entirely liver protein) is presumably converted into plasma protein. Gelatin alone added to the liver basal diet causes very little if any extra plasma protein production. The addition to gelatin of cystine, or tyrosine, or tryptophane, or of both tyrosine and tryptophane has little or no effect on its potency for plasma protein production. When gelatin is supplemented by cystine and either tryptophane or tyrosine, 25 to 40 per cent of the protein content of the combination is converted into plasma protein—an efficiency equaling that of any protein hitherto tested. Preliminary experiments indicate that methionine cannot substitute for cystine nor can phenylalanine substitute for tyrosine in the efficient combination of gelatin plus cystine plus tyrosine. Laked red blood cells given by vein afford little or no material for plasma protein formation. When the reserve stores of plasma protein building material are exhausted the dog can form little if any plasma protein during protein-free diet periods.
When blood plasma proteins are depleted by bleeding, with return of the washed red cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a uniform plasma protein production on a basal low protein diet. These dogs are clinically normal with normal appetite, no anemia and normal nitrogen metabolism. These dogs become test subjects by which various factors relating to plasma protein production may be tested. The normal dog (10 to 13 kg.) has a substantial reserve store of plasma protein building material (10 to 60+ gm.) which requires 2 to 6 weeks plasmapheresis for its complete removal. After this period the dog will produce uniform amounts of plasma protein each week on a fixed basal diet. Dogs previously depleted by plasmapheresis and then permitted to return to normal during a long rest period of many weeks, may show much higher reserve stores of protein building material in subsequent periods of plasma depletion (see Table 1). Under uniform conditions of low protein diet intake when plasmapheresis is discontinued for 2 weeks the plasma protein building material is stored quantitatively in the body and can subsequently be recovered (Table 4) in the next 2 to 3 weeks of plasmapheresis. Given complete depletion of plasma protein building reserve stores the dog can produce very little (2± gm. per week) plasma protein on a protein-free diet. This may be related to the wear and tear of body protein and conservation of these split products. Abscesses produced in a depleted dog during a fast may cause some excess production of plasma protein which is probably related to products of tissue destruction conserved for protein anabolism. Gelatin alone added to the basal diet causes very little plasma protein production but when supplemented by tryptophane gives a large protein output, while tryptophane alone is inert.
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