The effect of glucocorticoids on plasma insulin-like growth factor I concentration in the rat fetus

Radioimmuno- and radioreceptor-assayable insulin-like growth factor I (IGF-I) concentration was determined in plasma pools of rat fetuses on gestation day 21 following treatment of the pregnant rats with pharmacologic doses of betamethasone, dexamethasone, or cortisone on gestation days 12 and 13. Dose-related reduction of plasma concentration of IGF-I occurred after betamethasone or dexamethasone treatment. There was no change in IGF-I concentration after cortisone treatment. The changes in fetal IGF-I concentration after steroid treatment were parallel between the two assays. Comparison of the results with previous data showing the effects of identical treatment of pregnant rats on fetal body and organ growth suggests that the IGF-I changes correlate better with reduction of liver/body ratio than with reduction of body weight. The findings indicate that growth retardation after steroid treatment in the fetus is in part the result of factors other than IGF-I. This may include a direct effect of the glucocorticoids on skeletal tissue. Reduced IGF-I concentration may contribute to the growth deficit.