GH AND IGF-I DIFFERENTIALLY INCREASE PROTEIN-SYNTHESIS IN SKELETAL-MUSCLE AND JEJUNUM OF PARENTERALLY FED RATS

Growth hormone (GH) and insulin-like growth factor I (IGF-I) selective ly increase tissue mass. We compared the fractional rate of protein sy nthesis (K-s) in skeletal muscle, jejunal mucosa and muscularis, and l iver to investigate the differential effects of GH and IGF-I on tissue protein synthesis. Surgically stressed rats were maintained with hypo caloric total parenteral nutrition (TPN) and given recombinant human ( rh) GH (rhGH), rhIGF-I, rhGH + rhIGF-I (800 or 800 + 800 mu g/day, res pectively), or TPN alone. After 3 days, a flooding dose of valine (800 mu mol with 5.56 MBq L-[3,4-H-3]valine) was administered, and rats we re killed 20 min later. Body weight gain, nitrogen retention, and seru m IGF-I concentrations confirmed that GH plus IGF-I additively increas ed anabolism, Serum insulin concentrations were significantly increase d by GH and decreased by IGF-I. GH significantly increased K-s in skel etal muscle and jejunal muscularis, IGF-I significantly increased K-s in jejunal mucosa and muscularis, and neither GH nor IGF-I altered K-s in liver. GH and IGE-I differentially increase tissue protein synthes is in vivo.