Dihydralazine inhibits tyrosine hydroxylase in vivo in the rat.

The effect of dihydralazine on monoamine metabolism in the rat was investigated. Dihydralazine, 5 mg/kg i.v., reduced noradrenaline (NA) in the heart. After pretreatment with phenoxybenzamine an NA depletion was evident also in the brain. Dihydralazine did not affect the utilization of NA or dopamine in the brain as judged by the disappearance rates of these amines following synthesis inhibition by alpha-methyl-p-tyrosine. However, dihydralazine reduced the synthesis of monoamines as evidenced by a decreased accumulation of the monamine precursor dihydroxyphenylalanine (and 5-hydroxytryptamine) subsequent to treatment with NSD 1015. It is concluded that dihydralazine inhibits central tyrosine hydroxylase (and tryptophan hydroxylase) in the rat.