title: IGF-I treatment improves the functional properties of fast- and slow-twitch skeletal muscles from dystrophic mice.
abstract: Although insulin-like growth factor-I (IGF-I) has been proposed for use by patients suffering from muscle wasting conditions, few studies have investigated the functional properties of dystrophic skeletal muscle following IGF-I treatment. 129P1 ReJ-Lama2(dy) (129 ReJ dy/dy) dystrophic mice suffer from a deficiency in the structural protein, laminin, and exhibit severe muscle wasting and weakness. We tested the hypothesis that 4 weeks of IGF-I treatment ( approximately 2 mg/kg body mass, 50 g/h via mini-osmotic pump, subcutaneously) would increase the mass and force producing capacity of skeletal muscles from dystrophic mice. IGF-I treatment increased the mass of the extensor digitorum longus (EDL) and soleus muscles of dystrophic mice by 20 and 29%, respectively, compared with untreated dystrophic mice (administered saline-vehicle only). Absolute maximum force (P(o)) of the EDL and soleus muscle was increased by 40 and 32%, respectively, following IGF-I treatment. Specific P(o) (sP(o)) was increased by 23% in the EDL muscles of treated compared with untreated mice, but in the soleus muscle sP(o) was unchanged. IGF-I treatment increased the proportion of type IIB and type IIA fibres and decreased the proportion of type I fibres in the EDL muscles of dystrophic mice. In the soleus muscles of dystrophic mice, IGF-I treatment increased the proportion of type IIA fibres and decreased the proportion of type I fibres. Average fibre cross-sectional area was increased in the EDL and soleus muscles of treated compared with untreated mice. We conclude that IGF-I treatment ameliorates muscle wasting and improves the functional properties of skeletal muscles of dystrophic mice. The findings have important implications for the role of IGF-I in ameliorating muscle wasting associated with the muscular dystrophies.
authors: Department of Physiology, The University of Melbourne, Victoria 3010, Melbourne, Australia. g.lynch@physiology.unimelb.edu.au
authors: G S
authors: GS
authors: Lynch
authors: S A
authors: SA
authors: Cuffe
authors: D R
authors: DR
authors: Plant
authors: P
authors: P
authors: Gregorevic
mesh_terms: D000818:Animals; D048429:Cell Size / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D009137:Muscular Dystrophy, Animal / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D020388:Muscular Dystrophy, Duchenne / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D009929:Organ Size / Q000187:drug effects / Q000502:physiology
chemical_list: D007334:Insulin-Like Growth Factor I