Low birth weight in humans is predictive of insulin resistance and diabetes in adult life. The molecular mechanisms underlying this link are unknown but fetal exposure to excess glucocorticoids has been implicated, The fetus is normally protected from the higher maternal levels of glucocorticoids by fete-placental 11 beta-hydroxysteroid dehydrogenase type-2 (11 beta-HSD2) which inactivates glucocorticoids. We have shown previously that inhibiting 11 beta-HSD2 throughout pregnancy in rats reduces birth weight and causes hyperglycemia in the adult offspring. We now show that dexamethasone (a poor substrate for 11 beta-HSD2) administered to pregnant rats selectively in the last week of pregnancy reduces birth weight by 10% (P < 0.05), and produces adult fasting hyperglycemia (treated 5.3 +/- 0.3; control 4.3 +/- 0.2 mmol/liter, P = 0.04), reactive hyperglycemia (treated 8.7 +/- 0.4; control 7.5 +/- 0.2 mmol/liter, P = 0.03), and hyperinsulinemia (treated 6.1 +/- 0.4; control 3.8 +/- 0.5 ng/ml, P = 0.01) on oral glucose loading, In the adult offspring of rats exposed to dexamethasone in late pregnancy, hepatic expression of glucocorticoid receptor (GR) mRNA and phosphoenolpyruvate carboxykinase (PEPCK) mRNA land activity) are increased by 25% (P = 0.01) and 60% (P < 0.01), respectively, while other liver enzymes (glucose-6-phosphatase, glucokinase, and 11 beta-hydroxysteroid dehydrogenase type-1) are unaltered. Tn contrast dexamethasone, when given in the first or second week of gestation, has no effect on offspring insulin/glucose responses or hepatic PEPCK and GR expression, The increased hepatic GR expression may be crucial, since rats exposed to dexamethasone in utero showed potentiated glucose responses to exogenous corticosterone. These observations suggest that excessive glucocorticoid exposure late in pregnancy predisposes the offspring to glucose intolerance in adulthood, Programmed hepatic PEPCK overexpression, perhaps mediated by increased GR, may promote this process by increasing gluconeogenesis.