Pharmacological profile of octopamine receptors on the lateral oviducts of the locust, Locusta migratoria

Abstract

The pharmacological properties of octopamine receptors lying on the lateral oviducts of Locusta migratoria have been examined. These receptors mediate an elevation in cyclic AMP indicating that they may be octopamine-2 receptors. This was further clarified with the use of agonists and antagonists. The α-adrenergic agonists, clonidine and naphazoline, induced small increases in cyclic AMP levels, whereas tolazoline had no effect. Of the formamidine pesticides tested, demethylchlordimeform was found to be a potent, though partial agonist, whereas chlordimeform was a weak agonist. The effects of demethylchlordimeform and d,l-octopamine together were not additive indicating that they may be acting upon the same receptors. A number of aminergic antagonsits were capable of blocking octopamine-mediated elevations in cyclic AMP. The IC 50 values indicated a rank order of potency of phentolamine > gramine > metoclopramide > mianserin > cyproheptadine > yohimbine. The rank order on demethylchlordimeform-mediated elevations in cyclic AMP was the same for selected antagonists, again indicating that demethylchlordimeform was acting upon the same receptors as octopamine. The pharmacological profile of these octopamine receptors supports their classification as octopamine-2 receptors.