Adrenergic Activities of Octopamine and Synephrine Stereoisomers

Abstract

Both m-OA and p-OA are known to occur in the mammalian sympathetic nervous system where they are taken up in NA nerve terminals, accumulated in storage vesicles and released together with NA (Ibrahim et al, 1985). It is probable that both amines are released with NA as co-transmitters as proposed for p-0A by Axelrod and Saavedra (1977). Although all nerves probably contain two or more co-transmitters (O’Donohue et al, 1985), little is known about the mechanism of neuromodulation produced by the release of multiple co-transmitters. m-OA and p-OA are structurally so similar to NA that it is reasonable to suppose that their actions might be mediated by one or more of the well-characterized adrenoceptors. The physiological effects of p-0A and m-0A were first determined with racemates, and later some investigations were performed with poorly characterized enantiomers. The latter experiments were carried out on selected in vivo responses before the different subtypes of adrenoceptors were recognized. The activities of the pure (-) and (+) forms of m ^- and p-OA on α–1, α–2, β–1 and β–2 adrenoceptors have now been determined (Brown et al, 1987; Jordan et al, 1987).