Some Effects of Methionine on the Utilization of Nitrogen in the Adult Dog

Publisher Website
Google Scholar
Abstract
The addition of dl-methionine to a protein-free diet or to diets containing casein or egg white will reduce the excretion of nitrogen in adult dogs. The excretion remains lower than control values for several days after the amino acid has been removed from the diet. The addition, therefore, of methionine to these diets spares nitrogen in the animal, the sparing action being more marked in the presence of casein than of egg white. The relationship in normal adult dogs between nitrogen balance and absorbed casein nitrogen supplemented with methionine is linear in the region of negative nitrogen balance and curvilinear in the region of positive nitrogen balance. The slope of the line in the region of negative nitrogen balance (nitrogen balance index) increases from 0.8 in unsupplemented to from 1.5 to 1.6 in methionine supplemented casein. Slopes greater than unity prove that the addition of methionine to casein spares body and dietary nitrogen in the animal. This sparing action decreases rapidly in the region of positive nitrogen balance where the slope is a decreasing variable. A definite quantity of methionine is required to produce the maximum nitrogen sparing action. The addition of 0.025 gm of methionine nitrogen to 1.0 gm of casein nitrogen produces a maximum nitrogen balance index of approximately 1.5. The addition of larger quantities of methionine to the casein does not alter this index. Methionine produces the nitrogen sparing action through a reduction in the excretion of urea nitrogen, the ratio between ammonia nitrogen and urea nitrogen being increased.