MYOFIBRILLAR PROTEIN CATABOLISM IS RAPIDLY SUPPRESSED FOLLOWING PROTEIN FEEDING

The immediate response of protein degradation to food intake and the f actors for its regulation in rat skeletal muscle were examined. The co ncentration of N-tau-methylhistidine (MeHis) in serum and the rates of MeHis release from isolated soleus and extensor digitorum longus musc les were reduced in the period from 3 to 6 h after refeeding, indicati ng that the rate of myofibrillar protein degradation in the rat decrea sed immediately after refeeding. Changes in the serum concentration of insulin and corticosterone were not synchronized with those in the my ofibrillar protein degradation. When rats were fed on a protein-free d iet, no reduction of serum MeHis concentration or of the rate of MeHis release from isolated muscles after refeeding was apparent. Furthermo re, there was a tendency toward suppressing myofibrillar protein degra dation with a higher protein content of the diet. These results sugges t that the suppression of myofibrillar protein degradation by food int ake was regulated by dietary proteins.