THE EFFECTS OF OCTOPAMINE ARE MEDIATED VIA A G-PROTEIN IN THE OVIDUCTS OF LOCUSTA-MIGRATORIA

D,L-Octopamine, a biogenic amine, is present in the innervation of the oviducts of Locusta migratoria. Octopamine decreases both basal tonus and induced contractions of the oviducts by increasing the intracellu lar messenger cyclic AMP through activation of adenylate cyclase. We h ave investigated the possibility that octopamine regulation of adenyla te cyclase occurs through a stimulatory G protein in the locust oviduc ts. Using western blotting we have identified two G(s) alpha proteins (MW 39,000 and 51,000) in the oviduct muscle, which are specific for a ctivating adenylate cyclase. Activation of G(s) alpha with the G prote in ribosylating agent cholera toxin, resulted in a dose-dependent incr ease in cyclic AMP in the oviducts as measured by radioimmunoassay. Th is increase was potentiated in the presence of the phosphodiesterase i nhibitor IBMX. Pertussis toxin had no effect on cyclic AMP levels indi cating that a G(i) is not involved in cyclic AMP regulation. GTP gamma S, a hydrolysis resistant GTP analogue which constitutively activates G proteins, also resulted in a dose-dependent increase in cyclic AMP levels in the oviducts while GDP beta S had no effect. Moreover, incre ases in cyclic AMP induced by octopamine were potentiated in the prese nce of either cholera toxin or GTP gamma S. These results indicate tha t octopamine's effects are mediated, at least in part, by a stimulator y G protein in the locust oviducts.