1. Effect of source of dietary nitrogen on nitrogen balance and on plasma and urinary amino acids of man. 2. Effect of high protein or amino acid imbalanced diets on food intake, growth, serine dehydratase activity and plasma amino acids in growing rats
Dissertation Abstracts B, The Sciences and Engineering 30: 1774
Six young men retained similar amounts of N whether 5.50 g of the total daily intake of 6.28 g N was casein or 8 amino acids patterned as in casein, but retained less when that amount of N was supplied as essential amino acids with glycine and diammonium citrate or glycine, diammonium citrate and glutamic acid. Men retained more N with casein or amino acids simulating casein at daily intakes of 3600 to 3800 than at intakes of 3100 to 3300 kcal. After casein meals, most plasma amino acids decreased or remained at fasting levels but after the amino acid mixture simulating casein all plasma amino acids increased during the 1st then decreased during the 2nd h. When the essential amino acid mixture was given with glycine and diammonium citrate with or without glutamic acid, individual essential amino acids of plasma increased during the 1st h and remained high during the 2nd h. Fasting and post-prandial levels of histidine and proline were lower and that of arginine was slightly lower when those amino acids were omitted from the diet. Fasting plasma glycine and threonine, postprandial plasma glycine and urinary glycine, serine, threonine and taurine were higher when glycine and diammonium citrate with or without glutamate supplied all dietary non-essential N. When rats previously on a low protein intake were given a high-protein diet their food intake decreased, although protein intake and plasma amino acids increased. As liver serine-threonine dehydratase, which was low when the rats were on low-protein diet, increased so did food intake. When rats adapted to a low-protein diet were given a diet containing 5% casein and 6% of an amino acid mixture devoid of histidine, most plasma amino acids increased but plasma histidine and initially food intake and growth decreased. With time on the imbalanced diet liver serine-threonine dehydratase increased slowly, plasma serine and threonine decreased progressively and food intake and growth started to increase. Liver serine-threonine dehydratase in rats adapted to a high-protein diet decreased when the animals were given 5% casein and 6% amino acid mixture devoid of histidine. Food intake and growth did not alter initially but decreased when serine-threonine dehydratase had fallen and plasma serine and threonine had risen significantly. When rats adapted to a high-protein diet were given diets containing 12 or 18% of the amino acid mixture devoid of histidine, plasma amino acids rose and food intake and growth decreased.