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The Effect of Force Feeding a Tryptophan-deficient Diet on Arterio-Venous Difference of Plasma Amino Acids Across Skeletal Muscle of Rats

Department of Agricultural Chemistry, The University of Tokyo, Bunkyo-Ku, Tokyo 113, Japan

Young male rats were fed a tryptophan-free diet ad libitum or by force-feeding for 4 days, and were compared with rats fed a complete diet under similar conditions. Growth and nitrogen retention decreased markedly in rats fed the tryptophan-free diet regardless of differences in feeding method. The large aggregates of hepatic polysomes were decreased when a tryptophan-free diet was fed ad libitum, but they were increased in rats receiving the same diet by force-feeding. In the postabsorptive phase after feeding the tryptophan-free diet, free tryptophan concentration in the liver was significantly decreased. Net release of free tryptophan from the non-hepatic splanchnic bed was increased, as reflected in negative arterio-portal venous differences. Net uptake by hind leg muscle, as reflected in positive arterio-iliac venous differences, was decreased. Similar results were also obtained in rats force-fed the complete diet, which was accompanied by an increase in net release of most amino acids from the hind leg muscle. These findings suggest that the change in free tryptophan concentration in the liver or the supply from extrahepatic tissues into the liver at the postabsorptive phase may not be sufficient to explain the stimulated hepatic polysome aggregation by force-feeding of a tryptophan-free diet, and that the utilization of amino acids by extrahepatic tissues can be influenced by feeding procedures per se.

KEY WORDS: • tryptophan-deficiency • force-feeding • plasma free amino acids • hepatic polysomes

¹ Present address, Laboratory of Nutritional Chemistry, Department of Food Science, Kyoritsu Women's University, Tokyo, Japan.

Manuscript received 30 August 1977.