Protein synthesis was estimated in vivo in breast (superficial pectoral) and tibia (gastrocnemius) muscles, liver, kidney, pancreas, crop, duodenum, jejunum and ileum, using L-[U-14C]lysine injection. The effect on incorporation of [14C]lysine 1 and 2 h after injection was examined in five chickens adapted or not adapted to intermittent feeding. 2. Incorporation of [14C]lysine into tissue decreased in magnitude in the following descending order: pancreas greater than jejunum, duodenum greater than ileum, crop, liver greater than kidney greater than tibia, breast muscle and blood plasma. 3. The incorporation of [14C]lysine into muscle protein was higher in chicks after 24 h of refeeding than after 24 h of food deprivation. These differences were higher in adapted than in non-adapted birds. On days of refeeding the rate of incorporation exceeded that found in chickens fed ad lib. 4. Bound 14C from lysine in the intestinal segments was less than in control birds after food deprivation and greater after refeeding in non-adapted chicks only. 5. A negative relation was observed between bound and free 14C in muscles and in other tissues. 6. Short- and long-term adaptations to feeding regimens are discussed.
