Activity of dopamine‐β‐hydroxylase (DBH) and phenylethanolamine‐N‐methyl transferase (PNMT) in heart, lung and chromaffin tissue from the Florida spotted gar, Lepisosteus platyrhincus (Holostei)

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Abstract
The activities of dopamine‐β‐hydroxylase (DBH; E.C. 1.14.17.1) and phenylethanolamine‐N‐methyl transferase (PNMT; E.C. 2.1.1.10) were estimated in homogenates from the heart. the lung and the posterior cardinal veins from Lepisosteus platyrhincus. Both enzymes could be detected in all three tissues, the activity being highest in the chromaffin tissue of the posterior cardinal veins. The activity of DBH estimated in the present in vitro experiments was about 100‐fold higher than the PNMT activity. Preliminary experiments with substrate specificity for the PNMT shows a low (heart) or undetectable (lung and cardinal veins) methylation of phenylethylamine, and the specific PNMT inhibitor SK&F 64139 (1μM) lowered the PNMT activity in all three tissues by 55–75%. The presence of PNMT in the adrenergically innervated tissues puts Lepisosteus with the teleosts and the amphibians among vertebrates with capacity for truly adrenergic, as opposed to noradrenergic, transmission.