Pharmacological Characterisation of Octopamine-Sensitive Adenylate Cyclase in Periplaneta Americana

Octopamine (OA), the monohydroxyphenolic analogue of norepinephrine, occurs in high concentrations in nervous tissues and hemolymph of many invertebrates and in sympathetically innervated tissues of vertebrates (Hicks, 1977; Bailey et al., 1984). In insects, OA functions as a neurotransmitter, neuromodulator and neurohormone (Orchard, 1982) and it has been proposed as the sympathomimetic effector of physiological responses to excitation (Hoyle, 1975; Downer, 1979). The role of OA in vertebrates is uncertain although it has been suggested that specific receptors for OA are present in the rat brain and effects of OA on neuronal firing and potentiation of norepinephrine-mediated responses have been reported (Axelrod and Saavedra, 1977; Jones, 1984). The relatively low concentration of OA in vertebrate tissue and, by inference, the small population of specific OA-receptors have prevented investigation of the pharmacological properties of OA-receptors in vertebrates. By contrast, some insect tissues are highly sensitive to octopamine and, therefore, offer an excellent model system with which to study the pharmacology of OA-receptors.