Effects of nepicastat upon dopamine-β-hydroxylase activity and dopamine and norepinephrine levels in the rat left ventricle, kidney, and adrenal gland

Background and Objective: Evaluate the activity of dopamine-β-hydroxylase (DβH) as well as the effect of the DβH inhibitor nepicastat upon enzyme activity and levels of dopamine (DA) and norepinephrine (NE) in the rat left ventricle, kidney, and adrenal glands.Methods: DβH assay consisted of the enzymatic hydroxylation of tyramine into octopamine, and DA and NE tissues levels were quantified by HPLC-ED.Results: Nepicastat (30 mg/kg, p.o.) reduced DβH activity by 93% and 80% in the adrenals at 4 h and 8 h postdrug administration, accompanied by significant reductions in NE and epinephrine tissue levels and an increase in DA levels and of DA/NE tissue ratios, with similar findings for NE, DA and of DA/NE tissue ratios in left ventricle and kidney. DβH activity in the left ventricle and kidney showed a high degree of variability, which does not allow corroboration of the effects of nepicastat upon catecholamine tissue levels.Conclusion: The assay of DβH activity in heart and kidney lacks the necessary robustness, but DβH activity in the adrenals appears to be an appropriate marker. However, the effect size upon DA/NE tissue ratios (an indirect measure of DβH activity) as induced by nepicastat was very similar in sympathetically innervated tissues, left ventricle and kidney, and the adrenal medulla.