Influence of quantity of diet on protein synthesis of rats force-fed a threonine-devoid diet.

The influence of the quantity of diet on protein synthesis of rats force-fed a complete diet or one free of threonine for 3 days. Protein synthesis was studied. The results revealed that rats force-fed an adequate amount (6.5 gm. per day) of threonine-devoid diet demonstrated increased hepatic and cardiac protein synthesis and decreased skeletal muscle and splenic protein synthesis in comparison to the results with rats force-fed the complete diet. In contrast, rats force-fed one-half the quantity (3.25 gm. per day) of the diets revealed no or small differences in protein synthesis of the liver, heart, gastrocnemius muscle, and spleen between the rats force-fed the complete and the threonine-devoid diets, although both of the one-half quantity groups had values which were decreased in comparison to those of rats force-fed the adequate quantity of complete diet. The tube feeding of L-threonine (60 mg.) to rats force-fed one-half the quantity of the complete or threonine-devoid diet on the 4th morning 2 hours before killing did not influence the results of organ protein synthesis. Protein synthesis was studied in vivo by measuring 14C-leucine incorporation into organ proteins and in vitro by measuring 14C-leucine incorporation into proteins by using postmitochondrial supernatants or microsomes of livers. Sucrose density gradients of hepatic polyribosomes were studied and revealed that there were more aggregated polyribosomes in rats force-fed adequate quantities of the experimental diets than in those force-fed the control diets. Rats force-fed one-half quantity of the complete and threonine-devoid diets revealed similar polyribosomal patterns which revealed more disaggregation than those in rats ofrce-fed the adequate quantity of complete diet.