THE ACTION OF PHENYLIMINOIMIDAZOLIDINES AND 2-AMINOOXAZOLINE ON OCTOPAMINE RECEPTORS ON LOCUST FAT-BODY

Octopamine exerts many of its actions through receptors associated with the activation of adenylate cyclase. Thus, octopamine mediates elevations in cyclic AMP levels of a number of target tissues. The present study examines the action of two recently described classes of novel octopamine agonists with pesticidal properties, the substituted phenyliminoimidazolidines (PIIs) and the 2-aminooxazolines, upon the cyclic AMP content of isolated fat body of locusts. Octopamine, in the presence of a phosphodiesterase inhibitor, elevates the cyclic AMP content of fat body in a dose-dependent manner. d-Octopamine and synephrine mimic the effects of dl-octopamine, with dopamine and serotonin being poor agonists. The substituted PIIs, NC5 (2,6-diethyl PII) and NC7 (2-methyl-4-chloro PII) were full agonists of the octopamine receptor, while clonidine (2,6-dichloro PII) was a weaker agonist being only 57% as effective as octopamine at 10-4 M. The 2-aminooxazoline, AC6 [2-(4-chloro-o-toluidino)-2-oxazoline], was a full agonist with an essentially identical dose-response curve to octopamine itself. The accumulation of cyclic AMP stimulated by all four of these agonists was inhibited by phentolamine and gramine, two antagonists which also block the action of octopamine. The results confirm the agonistic properties of these novel compounds and illustrates their usefulness as tools for defining subtypes of octopamine receptors and as model compounds for the future development of pesticides directed against the octopamine receptor. © 1990.