Interactions between growth hormone and nutrition in hypophysectomised rats: skeletal muscle myosin heavy chain mRNA levels.

The aim of this study was to examine the role of growth hormone (GH) in regulating muscle phenotype and to determine how this is modulated by altered nutrition. Total RNA was extracted from gastrocnemius muscles of hypophysectomised rats treated with saline, GH or GH but fed a restricted intake. Type 1, 2A, 2B, embryonic and neonatal myosin heavy chain mRNA levels were estimated by slot blot hybridization. Hypophysectomy reduced the concentrations of types 1, 2A and embryonic mRNAs and dramatically elevated types 2B and neonatal compared to control levels, but this was time-dependent. All MHC mRNA levels were partially restored to control levels in the GH-treated rats except for type 1; the level of this transcript was only elevated by GH in the restricted intake group. Restricted food intake modulated the effects of GH administration for all other MHC mRNA concentrations.