Carbohydrate Metabolism and Physical Activity in Rats Fed Diets containing Purified Casein Versus a Mixture of Amino Acids Simulating Casein

Publisher Website
Google Scholar
Abstract
The effects of varying energy intake levels on physical activity and glucose metabolism were studied in young growing rats. Male rats 28 days of age were fed for 31 days diets containing either casein or an amino acid mixture simulating casein at 2 levels of calorie intake. Physical activity was measured and 14C recovery from injected glucose-1-14C, -6-14C, and -U-14C was determined as percentage of dose in expired CO2, feces, and urine, from one to 24 hours after giving each rat his daily ration. The average revolutions per day run was higher for calorie-restricted animals, but there was no significant difference in activity due to substituting the mixture of amino acids for casein, although casein-fed rats tended to be more active. This increase in physical activity caused by calorie restriction was due to a significant difference in daytime activity, as all rats were equally active in the dark. There were no significant differences due to calorie level or nitrogen source in 14CO2 recovery from glucose-6-14C and glucose-U-14C, but amino acid-fed rats converted more glucose-1-14C to 14CO2 as measured cumulatively 6 and 23 hours after injection. Calorie-restricted rats expired less glucose-1-14C as 14CO2 during the first 6 hours after injection, but this effect was not evident after 23 hours. There was a trend toward lower 14C recovery from glucose-U-14C in urinary citrate of amino acid-fed rats, although urinary citrate excretion was unaltered by diet. These data indicate a greater utilization of alternative pathways to the glycolytic scheme and tricarboxylic acid cycle for metabolism of glucose in amino acid-fed rats and several possible explanations are discussed.