Developmental and steroid hormonal regulation of insulin-like growth factor II expression.

We have investigated the influence of steroid hormones on insulin-like growth factor II (IGF-II) expression. Hepatic IGF-II mRNA decreased gradually during postnatal development, reaching adult levels at 3 weeks of age. Treatment of 1-day-old rats for 4 days with 10 micrograms/day of the glucocorticoid dexamethasone (DEX) reduced IGF-II mRNA levels 10-fold in liver and inhibited body weight gain. Estradiol and testosterone did not affect IGF-II expression. A dose-response relationship between IGF-II mRNA levels and the different amounts of DEX injected was seen. IGF-II levels remained low after withdrawal of DEX, indicating an irreversible effect. Albumin expression was increased in newborn rat livers after DEX treatment. Our results suggest that glucocorticoids play an important role in the regulation of IGF-II expression. The mechanism for glucocorticoid-induced reduction of IGF-II mRNA is still unclear; however, our findings indicate that DEX inhibits IGF-II by causing premature differentiation of the liver.