THE EFFECT OF FASTING ON LEUCINE DEGRADATION IN CHICK SKELETAL MUSCLE

Abstract

In vitro degradation of leucine in intact extensor digitorum communis muscles from fed and from 12- and 24-h-fasted 10-day-old broiler chicks was investigated. The net rate of leucine transamination and the rates of oxidative decarboxylation, oxidation of carbons 2–6 and total CO2 production from 14C-labelled leucine increased (P < 0.01) from 0.57 ± 0.03, 0.42 ± 0.02, 0.95 ± 0.07 and 1.37 ± 0.09 nmol h−1 mg muscle−1 for the fed group to 0.79 ± 0.05, 0.60 ± 0.04, 1.34 ± 0.04 and 1.94 ± 0.10 nmole h−1 mg muscle−1, respectively, following 24 h fasting. The values for the same rates following 12 h fasting were 0.60 ± 0.02, 0.44 ± 0.02, 1.04 ± 0.05 and 1.47 ± 0.06 nmol h−1 mg muscle−1, respectively, and were significantly (P < 0.01) less than the values obtained following the 24 h fast. The values obtained for the rates of leucine catabolism in muscles from the 12-h-fasted group did not differ (P > 0.05) from the values obtained in muscles from the fed group. These results demonstrate that the rate of leucine catabolism in the skeletal musculature of the chick is increased during fasting. Increased leucine degradation provides energy for muscle metabolism and constitutes a mechanism whereby chicks are able to adapt to fasting. Key words: Leucine degradation, skeletal muscle, fasting, chicks