PRE‐ AND POSTJUNCTIONAL EFFECTS OF CLONIDINE‐ AND OXYMETAZOLINE‐LIKE COMPOUNDS IN GUINEA‐PIG ILEAL PREPARATIONS

Abstract

1 Noradrenaline and 28 imidazolidine (clonidine-like) and imidazoline (oxymetazoline-like) compounds with various phenyl ring substituents have been examined for their ability to inhibit responses to transmural stimulation and exogenous acetylcholine in ileal preparations from reserpine-treated guinea-pigs. 2 The bathing solution contained propranolol, mepyramine, cimetidine and desipramine to preclude interference with the responses by other than the α-receptor-mediated actions of the compounds. 3 In transmurally stimulated preparations the inhibitory response to noradrenaline is due to a combination of prejunctional α-adrenoceptor stimulation and a postjunctional depressant effect that does not involve adrenoceptor activation. 4 Of the 28 imidazolidines and imidazolines studied, 21 inhibited transmurally elicited responses. In the various compounds studied this effect involved actions at pre- or postjunctional sites as indicated by (a) the frequency-dependence of the inhibitory response, (b) its susceptibility to blockade by α-receptor antagonists and (c) the relative concentrations required to inhibit responses to transmural stimulation and exogenous acetylcholine.