N-acetylation of p-octopamine by Malpighian tubules and other tissues of the American cockroach, Periplaneta americana L., in vitro

The capacity of several tissues of the American cockroach, Periplaneta americana, to remove p-octopamine from incubation medium was investigated using high performance liquid chromatography with electrochemical detection to monitor levels of p-octopamine and the N-acetylated derivative. Gut was the most active tissue in removing p-octopamine from the medium and separate analyses of the various regions of the gut indicate that the Malpighian tubules constitute the primary site of removal. Epidermal and nervous tissue are also capable of removing substantial amounts of p-octopamine. In addition to the removal of p-octopamine, Malpighian tubules remove dopamine and 5-hydroxytryptamine from incubation medium and, indeed, have a slightly greater capacity for removing these monoamines than for removing p-octopamine. However, concentrations of each amine that are considerably in excess of physiological levels do not saturate the system. Most of the p-octopamine removed by the gut tissue undergoes N-acetylation to form N-acetyl-p-octopamine; thus, this appears to be the primary degradation metabolic route for p-octopamine. Analysis of the faeces following injection of p-octopamine demonstrated the presence of both p-octopamine and the N-acetylated derivative.