THE EFFECT OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) ON PROTEIN-TURNOVER IN THE MEAT-TYPE CHICKEN (GALLUS-DOMESTICUS)

Insulin-like growth factor-I (IGF-I) effects on chicken growth and dev elopment are poorly understood. This study examined the effect of IGF- I on protein synthesis rates in various tissues in the male broiler ch icken. At three weeks of age, osmotic minipumps were subcutaneously im planted in the scapular area. Chickens were infused with either chicke n IGF-I (450 mu g/kg BW/day) or saline. After treatment for 5 days, th e chickens received a flooding dose of [H-3]-phenylalanine, and were s acrificed 20 min later. Wing vein blood samples were taken at 0, 5, 10 and 20 min post-injection. The following tissues were removed and fro zen for analysis: pectoralis muscle, gastrocnemius muscle, heart, live r, and small intestine. In vivo total protein synthesis measurements w ere made using the double-label technique. Contractile protein degrada tion was evaluated using intracellular free 3-methylhistidine concentr ations in skeletal muscle. There were no significant differences in ab solute or relative body growth rates over the treatment period. Skelet al muscle (pectoralis and gastrocnemius) weights were significantly de creased with IGF-I treatment, while heart weight was significantly inc reased. Plasma insulin levels were significantly lower in IGF-treated chickens compared to that in control birds. There was no effect of IGF -I on protein synthesis rates in any of the tissues examined. Intracel lular free 3-methylhistidine concentrations were higher in both the ga strocnemius (17%) and pectoralis muscles (25%) of chickens treated wit h IGF-I. This data demonstrates that IGF-I may have an indirect effect to regulate muscle protein turnover rates. (C) 1998 Elsevier Science Inc.