m‐Octopamine: Normal Occurrence with p‐Octopamine in Mammalian Sympathetic Nerves

Abstract

The development of a radiochemical enzyme assay for p‐octopamine in 1969 led to its identification in a large number of invertebrate nerve systems and in mammalian sympathetic nerves. The original method by which p‐octopamine was measured has now been found to be nonspecific; however, modifications of this procedure can determine both m‐ and p‐octopamine. We recently developed a new specific method for the unequivocal identification and quantitative determination in tissue of the six octopamine and synephrine isomers. With this method—negative chemical ionization gas chromatography‐mass spectrometry—the more physiologically active m‐octopamine has been found in association with p‐octopamine in 10 organs of the rat. m‐Octopamine is present in concentrations equal to those of p‐octopamine in heart, spleen, and liver and in concentrations from 30 to 60% of p‐octopamine in adrenals, vas deferens, brain, kidney, large intestine, bladder, and lungs. In vivo inhibition of monoamine oxidase markedly increased the concentrations of both m‐ and p‐octopamine in all organs examined. Both amines were virtually absent from all organs except the adrenals following chemical sympathectomy with 6‐hydroxydopamine, thereby establishing that m‐ and p‐octopamine are localized within sympathetic nerve endings. Copyright © 1985, Wiley Blackwell. All rights reserved