Effect of chronic AICAR treatment on muscle fiber composition and enzyme activity in skeletal muscle of rats

Muscle fiber is the basic unit of skeletal muscle. Muscle fiber types play a crucial role in improving meat quality. In the current study, Wistar rats were chronic injected with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) for four weeks in order to define the 5 '-AMP-activated protein kinase (AMPK) protein activity on muscle fiber composition, enzyme activity and the mRNA expression of muscle fiber type-related genes in gastrocnemius (GS) muscle. Food intake and body weight did not show a significant difference after AICAR treatment (P > .05). The AICAR treatment caused a significantly increased number and area proportion of type I muscle fiber and expression level MyHC I mRNA (P < .05), succinic dehydrogenase (SDH) and malate dehydrogenase (MDH) activities (P < .05), but decrease in the number proportion of type IIB muscle fiber and MyHC IIb and MyHC IIx mRNA level (P < .05). The Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha) mRNA level (P < .05) was increased and glucose transporter 4 (GLUT-4) mRNA level tended to be higher (P = .052) in the AICAR group. These results demonstrated that chronic AICRA treatment induces oxidative muscle fiber switching, enhances oxidative enzyme activity and GLUT4 mRNA level, mediated by PGC-1 alpha.