The effect of food restriction on circulating insulin-like growth factor-I in mice divergently selected for high or low protein or fat to body mass ratios

1. Plasma insulin-like growth factor-I (IGF-I) was measured in mice divergently selected for high and low lean tissue gain or high and low fat to body weight ratio, both before and after fasting and refeeding. 2. Selection for high lean tissue resulted in increased body weight and a higher basal IGF-I concentration at 10 weeks of age. 3. Selection resulting in a difference in fatness had no effect on IGF-I concentration. 4. Circulating IGF-I decreased more rapidly in response to 24 hr food withdrawal in growing (5-week-old) than in almost fully grown (10-week-old) animals from all lines.