PARALLEL INSULIN-LIKE GROWTH-FACTOR-I AND INSULIN-RESISTANCE IN MUSCLES OF RATS FED A HIGH-FAT DIET

The possibility of a similarity between insulin-like growth factor-I ( IGF-I) and insulin resistance in epitrochlearis muscles of rats fed a high fat diet [20% (wt/wt) fat] vs. a low fat diet [5% (wt/wt) fat] wa s investigated. Half-maximally and maximally effective concentrations of IGF-I- and insulin-stimulated 3-O-methyl-glucose transport were 2.3 2 and 25 nM, respectively, for IGF-I, compared with 0.79 and 20 nM for insulin. The high fat diet reduced both responsiveness and sensitivit y of IGF-I-stimulated 3-O-methyl-glucose transport in parallel with th e impaired insulin-stimulated 3-O-methyl-glucose transport. IGF-I bind ing at 2.5 nM to incubated epitrochlearis muscle was also decreased by the high fat diet (P < 0.05). Thus, the high fat diet caused simultan eous IGF-I and insulin resistance in rat skeletal muscle. The IGF-I re sistance induced by feeding the high fat diet seems at least partially due to a reduction in IGF-I binding.