Involvement of tyrosine hydroxylase up regulation in dexamethasone-induced hypertension of rats.

We investigated the effect of dexamethasone (DEX) on tyrosine hydroxylase (TH) mRNA level, and TH activity and catecholamine levels in the adrenal medulla of the rat. DEX (1 mg/kg/day, s.c.) was administered for 2 days, and a control group was given corn oil. DEX significantly increased systolic blood pressure. TH mRNA level, TH activity, epinephrine level, and norepinephrine level in the adrenal medulla of DEX-treated rats were significantly higher than those of control rats. Also, epinephrine and norepinephrine levels in plasma were significantly higher in DEX-treated rats than in controls. alpha-Methyl-p-tyrosine prevented the DEX-induced blood pressure increase. These results suggest that the catecholamine synthetic pathway may be involved in DEX-induced hypertension.