Anabolic effects of insulin-like growth factor I in calorie restricted and ad libitum fed rats
Yang, H. | Schalch, D.S. | Ney, D.M.
The anabolic effects of recombinant human IGF-I were studied in calorie-restricted and ad libitum fed male, Sprague-Dawley rats (129 +/- 6 g). Animals ingested 76% of the energy consumed by a reference group for 8 days. They were then continued on calorie restriction for 2 weeks (Exp. 1) or fed ad libitum for 1 week (Exp. 2) during which time IGF-treated animals received 200 microgram/day of IGF-I via subcutaneous osmotic minipumps. Serum IGF-I levels doubled in treated rats. In Exp. 1, growth rate nitrogen retention and feed efficiency were 30-43% greater in IGF-treated than control animals (p<0.01) during the first, but not the second week of IGF-I administration. In Exp. 2, feed efficiency was 16% greater (p<0.05) with IGF-I, but growth rate and nitrogen retention were not different. We conclude that doubling the serum concentration of IGF-I in growing rats enhances feed efficiency if either an ad libitum or calorie-restricted diet is consumed, and that stimulation of growth and nitrogen retention with IGF-I administration is greater when malnutrition is present.
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