Plasma levels of insulin-like growth factor-I are reduced at one week of age in monosodium L-glutamate-treated mice.

Administration of monosodium L-glutamate (MSG) to neonatal mice produces a hypothalamic syndrome consisting of stunted growth and later development of obesity. We assayed plasma insulin (IRI), thyroxine (T4) and insulin-like growth factor-I (IGF-I) to investigate their roles in the growth of the mice. Two mg/g body weight of MSG was injected into newborn male mice daily for five successive days after birth. Plasma IRI levels were increased on the after 8 weeks of age in MSG-treated mice. There was no significant difference between the plasma T4 levels in MSG-treated mice and those in controls at any age studied. In contrast to this, plasma IGF-I levels in MSG-treated mice were reduced at one week and after. These results suggest that a decreased plasma IGF-I level contributes to the retarded linear growth which develops soon after the administration of MSG, and hyperinsulinemia contributes to the later development of obesity in MSG-treated mice.