Effect of GH administration on GH and IGF-I receptors in porcine skeletal muscle and liver in relation to plasma GH-binding protein

The present study was undertaken to determine the effect of GH administration on GH and IGF-I receptors in skeletal muscle compared with liver in growing pigs. Plasma IGF-I and GH-binding protein (GHBP) levels were also determined. Twelve Large White pies (castrated males) were treated daily with 100 mu g pituitary porcine GH (pGH) per kg body weight or vehicle for 41 days intramusculary. Relative to controls, pGH administration increased plasma IGF-I concentrations by 3.3-fold. Administration of pGH had no effect on plasma GHBP levels. Tn liver,I-125-labelled bovine GH (bGH)-specific binding (P<0.05) and GH receptor (GHR) mRNA levels (P<0.05) were higher in pGH-treated than in control pigs. In longissimus dorsi (LD), I-125-labelled bGH specific binding did not differ significantly between the two groups while GHR mRNA levels (P<0.05) were lower in pGH-treated than in control pigs. Administration of pGH had no effect on I-125-labelled bGH-specific binding and GHR mRNA levels in trapezius (TR). I-125-Labelled IGF-I-specific binding in liver was unaffected by PGH administration. Similarly, in liver, LD and TR, IGF-I receptor mRNA levels were not different between pGH-treated and control animals. It can be concluded that (1) GH binding and IGF-I receptor mRNA are not affected by GH in skeletal muscle, (2) GH influences GHR in a tissue-specific manner and (3) hepatic GHR and GHBP levels are not co-regulated.