The effect of dietary protein deficiency and realimentation on serum growth hormone and insulin-like growth factor-I in growing mice

Many of the effects of dietary protein deficiency may be attributed to changes in circulating pituitary-derived growth hormone (GH) and hepatic- derived insulin-like growth factor I (IGF-I). To characterize the effect of dietary protein deficiency and realimentation on concentrations of serum GH and IGF-I, 100 weanling female BALB/c mice were fed either a control diet with 20% casein (20C), a low-protein isocaloric diet with 4% casein (4C) for 2, 4, 6, or 8 weeks, or 4C for 6 weeks followed by 2 weeks of realimentation with 20C. Serum GH and IGF-I concentrations, body weight, tail length, pituitary weight, and hypothalamic weight were evaluated. Mice fed 4C exhibited a significantly lower rate of body weight and tail length growth than mice fed 20C. The realimented mice had a significant recovery in body weight gain and tail length. Concentrations of serum GH and IGF-I were consistently lower in mice fed 4C compared with 20C, while the realimented mice exhibited a recovery in serum IGF-I, but not serum GH. There were no significant differences between 20C-fed and 4C-fed mice for pituitary and hypothalamic weights. However, the realimented mice had a significant reduction in pituitary and hypothalamic weights. The results suggest that dietary protein deficiency decreases the overall growth of mice due to decreased serum GH or IGF-I, but growth recovery during realimentation is correlated specifically to an increase in serum IGF-I but not GH.