The Effect of Protein and Amino Acid Metabolism of the Urea and Xylose Clearance

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Abstract
The post-absorptive urea and xylose clearances in dogs maintained on a basal diet are low and constant from day to day, and feeding the basal diet has itself little effect on these clearances. The feeding of meat produces a gradual and prolonged post-prandial rise in both clearances relative to the levels existing before the meal. When meat is used as a maintenance diet over a period of 2 or 3 weeks the post-absorptive clearances are elevated, while the post-prandial effects of eating meat are not obliterated. A casein diet has qualitatively the same effect in elevating the urea and xylose clearances as has meat. The administration of thyroxin to a dog maintained on a basal diet, and the administration of phlorizin to a fasting dog, likewise elevate the urea and xylose clearances above their respective post-absorptive levels. These facts indicate that protein metabolism as such, whether endogenous or exogenous, is responsible for the increase in renal function. Feeding a basal diet in which a part of the carbohydrate has been replaced by glycine has the same qualitative effect upon the post-absorptive and post-prandial urea and xylose clearances as has meat; and the subcutaneous or intravenous administration of glycine, glycylglycine and alanine induces immediate but moderate increases in renal activity, whereas glucose is without effect. It would, therefore, appear that the primary effect of protein upon renal function is a result of the action of the amino acids, or of the hydroxy acids produced in the course of their metabolism, upon glomerular activity.

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