Abstract
Three experiments were conducted to study effects of the dietary protein level a) on the restoration of hepatic lipogenesis in fasted chicks by the administration of glucose and the amino acid mixture, b) on the 14C incorporation from [U-14C] glucose and [U-14C] tyrosine into hepatic fatty acids and c) on the hepatic activities of glycolytic and gluconeogenic enzymes. In chicks fed the 17% protein diet, the reduced rate of fatty acid synthesis by fasting was completely restored by the administration of glucose. In fasted chicks pre-fed the 67% protein diet, on the contrary, no restoration of lipogenesis occurred by the administration of glucose, but administering the amino acid mixture, which was so made as to correspond to the amino acid composition of soybean protein, increased the reduced rate of lipogenesis to about 33% of the pre-fasting level. The rate of 14C incorporation from [U-14C] glucose into fatty acids was considerably slow in chicks fed the 67% protein diet, whereas the 14C incorporation from [U-14C] tyrosine showed a much higher rate than did that from [U-14C] glucose. The activities of hexokinase, phosphofructokinase and pyruvate kinase (glycolytic enzymes) decreased by increasing the protein level of diet, whereas fructose-1, 6-diphosphatase and phosphoenolpyruvate carboxykinase (gluconeogenic enzymes) activities increased. These results suggest that, in chicks fed a high-protein diet, hepatic fatty acids may be synthesized from amino acids, but not from glucose, which would probably be the result of the decreased avail-ability of glucose due to the lowering of glycolytic enzyme activity.
