title: [The effect of the beta-adrenergic agonist clenbuterol on the growth of skeletal muscles of rats].
abstract: The effects of clenbuterol (CB) on the weights of 6 hindleg muscles as well as on structural and biochemical characteristics of extensor digitorum longus muscle (EDL) were studied on Wistar rats. Different CB-doses (5 vs. 18 mg/kg diet) were tested and rats of different sex were used. The 12 days treatment accelerated the growth of the 6 hindleg muscles by 13 to 24% without predominant response of fast twitch or slow twitch muscles. The higher muscle weights were achieved by fibre hypertrophy as demonstrated by increased fibre diameters (+13 to +16%), and not by fibre multiplication. There was no evidence for a selective fibre hypertrophy of one of the metabolic fibre types. Fibre type composition shifted to the fast glycolytic fibres (FTG +0.7 to +4.9%-units). There were no significant differences in responses between the sexes of CB-doses. Clenbuterol decreased the nucleus/cytoplasm ratio, measured as nuclei number/mm2 fibre area, between 24 and 28% and the DNA/protein ratio by 17%. RNA content and RNA/DNA ratio were enhanced by 25 and 22%, respectively; the protein/RNA ratio remained unchanged. The results suggest that clenbuterol changes fibre type composition and stimulates fibre growth in a pretranslational stage of protein synthesis without addition of nuclei by satellite cell proliferation.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002976:Clenbuterol / Q000494:pharmacology*; D004247:DNA / Q000032:analysis; D005260:Female; D006614:Hindlimb; D006984:Hypertrophy; D008297:Male; D024510:Muscle Development; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects; D009124:Muscle Proteins / Q000032:analysis; D018482:Muscle, Skeletal / Q000737:chemistry / Q000187:drug effects* / Q000254:growth & development; D009929:Organ Size / Q000187:drug effects; D012313:RNA / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000318:Adrenergic beta-Agonists; D009124:Muscle Proteins; D012313:RNA; D004247:DNA; D002976:Clenbuterol
vernacular_title: Effekte des beta-Adrenergen Agonisten Clenbuterol auf das Wachstum der Skelettmuskulatur von Ratten.