Endocrinology, Vol 130, 1942-1950, Copyright © 1992 by Endocrine Society

ARTICLES

Differential actions of growth hormone and insulin-like growth factor-I on tissue protein metabolism in dwarf mice

JM Pell and PC Bates
Department of Endocrinology and Animal Physiology, Agricultural and Food Research Council Institute for Grassland and Animal Production, Hurley, Maidenhead, Berks, United Kingdom.

The actions and interactions of exogenous insulin-like growth factor-I (IGF-I) and bovine GH (bGH) on protein metabolism were investigated in vivo using Snell dwarf mice. Mice were administered a daily dose of 1.5 or 20 micrograms bGH in the presence or absence of 20 micrograms IGF-I. IGF-I and GH stimulated significant increases in whole body weight gain. Serum IGF-I concentrations increased dramatically in mice administered IGF-I, but more modestly in GH-treated mice. However, greater increases in tissue IGF-I content were observed for GH- than for IGF-treated mice, implying that GH exerted its anabolic actions by local IGF-I synthesis. Skeletal muscle (combined gastrocnemius plus plantaris) weight was significantly increased in GH-treated mice and tended to increase in IGF-treated mice. Muscle protein synthesis was stimulated by about 50% in mice treated with IGF-I alone and the lower dose of GH and by over 100% in the group treated with 20 micrograms/day GH compared with that in saline-treated mice; further additive increases in synthesis rates were observed for mice administered both IGF-I and GH. In all cases, this stimulation was due to both increased RNA content and efficiency of protein synthesis, expressed as grams of protein synthesized per g RNA/day. Liver weight and protein synthetic rate were increased by as much as 25% and 34%, respectively, in GH- treated mice, but IGF-I inhibited hepatic protein metabolism, tending to decrease synthesis rates and inducing a decrease in the efficiency of protein synthesis. Thus, IGF-I and GH have specific and differential effects on tissue protein metabolism in this model.

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