Effect of morphine on tyrosine hydroxylase activity in mouse brain

Abstract

Effects of morphine on the in vitro and in vivo activity of tyrosine hydroxylase in mice brain were investigated by measuring the conversion of 14C-tyrosine to DOPA and catecholamine, respectively. In in vitro experiments, morphine (10 −5−10 −3 M) did not modify the activity of tyrosine hydroxylase in brain homogenate, while in in vivo experiments, the activity of tyrosine hydroxylase in the brain was significantly increased after administration of morphine, 20 mg/kg. The above findings suggest that morphine activates tyrosine hydroxylase activity through a feedback mechanism in vivo.