Abstract
Skeletal muscles are capable of adapting themselves to a variety of exercise stimuli with varied changes in their mechanical and metabolic properties. Muscle hypertrophy is induced by stretching of matured muscles in vivo. On the contrary, muscle atrophy is induced by some models of reduced neuromuscular activity. However, little data are available for the intracellular changes of skeletal muscle hypertrophy and atrophy irrespective of a variety of techniques. Therefore, it is useful to use the β2-agonist (clenbuterol : CLE)-induced muscle hypertrophy and whole body suspension (WBS)-induced muscle atrophy. Male SD rats were used and divided into the control (CON) groups and the CLE administered (ADM) or WBS groups. CLE (1mg/kg BW/day) was administered for 30 days. WBS was carried out for 10 days. SOL and GAS muscles were used for muscle RNA, DNA and protein assays. Protein/RNA ratios of both muscles increased by 16-19% in ADM group. Protein/DNA ratios of both muscles increased by 11-37% in ADM group. Protein/DNA ratios of both muscles decreased by 32-39% in WBS group. RNA/DNA ratios of both muscles decreased by 28-39% in WBS group. In conclusion, SOL muscle hypertrophy by CLE may be at least partly related to the increases in DNA transcription and protein synthesis (=RNA/DNA) and apparent cell volume (=Protein/DNA). WBS-induced muscle atrophy may be accompanied by the decreases in Protein/DNA ratio and RNA/DNA ratio without changing ribosomal capacity (=Protein/RNA). [Jpn J Physiol 55 Suppl:S225 (2005)]
