PROTECTIVE EFFECT OF GLUTAMINE FROM GLUCOCORTICOID-INDUCED MUSCLE ATROPHY OCCURS WITHOUT ALTERATIONS IN CIRCULATING INSULIN-LIKE-GROWTH-FACTOR (IGF)-I AND IGF BINDING-PROTEIN LEVELS

We investigated whether the prevention of glucocorticoid-induced muscl e atrophy by glutamine infusion is associated with alterations in seru m levels of insulinlike growth factor (IGF)-I and its binding proteins (IGFBPs), Hormone (cortisol acetate [CA], 100 mg/kg body wt/day) and vehicle (carboxymethyl cellulose [CMC])-treated female rats were infus ed with either saline or glutamine (240 mM, 0.75 ml/hr) for a 7-day pe riod. Glutamine infusion prevented over 70% of the skeletal muscle mas s loss due to the glucocorticoid injections, Serum IGF-I concentration s, which were measured by radioimmunoassay (RIA) after acid solid-phas e extraction of IGFBPs, were not significantly different among groups (range of means: 373-395 ng/ml). Saline/CA treatment resulted in a 2-f old increase in circulating levels of IGFBP-3 (38- to 50-kDa bands fro m ligand blotting measurements) versus the saline/CMC group. Levels of 30- to 32-kDa bands were increased by similar to 3-fold in the CA-tre ated rats, Immunoprecipitation studies suggested that the increase in the 30- to 32-kDa binding proteins were not due to elevated levels of IGFBP-1, -2, or -5, None of the treatments significantly modified circ ulating levels of IGFBP-4 (24 kDa), Glutamine infusion did not reverse the effects of glucocorticoids on circulating levels of 38- to 50- an d 30- to 32-kDa IGFBPs. We conclude that the attenuation of glucocorti coid-induced muscle atrophy by glutamine infusion is not associated wi th changes in circulating levels of IGF-I or IGFBPs.