The effect of glococorticoids on the dopamine (DA)-mediated cyclic adenosine monophosphate (cAMP) by intact vascular smooth muscle cells (VSMC) was studied in rats. Cultured VSMC were obtained from renal arteries of 14-week-old Wlstar-Kyoto rats by explant method. Micromoiar concentrations of dexamethasone (DEX) pretreatment for 48 hours potentiated DA-mediated response without any change of affinity constant. However, micromoiar concentrations of aldosterone pretreatment for 48 hours had almost no effect on DA-mediated response. The DEX-induced facilitation began at 6 hours and reached maximum at 24 hours after DEX administration in a dose-dependent manner. Inhibitors of protein and RNA synthesis blocked this glucocorticoid effect. The basal activity of adenylate cyclase in DEXtreated cells was twofold higher than that in control cells. Treatment of VSMC with DEX increased cholera toxin-stimulated and forskolin-stimulated adenylate cyclase activity. However, pertussis toxin treatment did not augment or reduce the effect of DEX treatment. These results suggest that glucocorticoids increase DA-mediated cAMP formation by VSMC through glucocorticoid type II receptors and the induction of protein synthesis and that the activation of the catalytic unit may play some role in this facilitation.