The tricyclic antidepressants amitriptyline, nortriptyline and imipramine are weak antagonists of human and rat alpha1B-adrenoceptors.

F D Nojimoto, A Mueller, F Hebeler-Barbosa, J Akinaga, V Lima, L R de A Kiguti, A S Pupo

Department of Pharmacology, Instituto de Biociências, UNESP, Botucatu, SP, Brazil.

Neuropharmacology 2010 Jul-Aug

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Although it is long known that the tricyclic antidepressants amitriptyline, nortriptyline and imipramine inhibit the noradrenaline transporter and alpha(1)-adrenoceptors with similar affinities, which may lead to self-cancelling actions, the selectivity of these drugs for alpha(1)-adrenoceptor subtypes is unknown. The present study investigates the selectivity of amitriptyline, nortriptyline and imipramine for human recombinant and rat native alpha(1)-adrenoceptor subtypes. The selectivity of amitriptyline, nortriptyline and imipramine was investigated in HEK-293 cells expressing each of the human alpha(1)-subtypes and in rat native receptors from the vas deferens (alpha(1A)), spleen (alpha(1B)) and aorta (alpha(1D)) through [(3)H]prazosin binding, and noradrenaline-induced intracellular Ca(2+) increases and contraction assays. Amitriptyline, nortriptyline and imipramine showed considerably higher affinities for alpha(1A)- (approximately 25- to 80-fold) and alpha(1D)-adrenoceptors (approximately 10- to 25-fold) than for alpha(1B)-adrenoceptors in both contraction and [(3)H]prazosin binding assays with rat native and human receptors, respectively. In addition, amitriptyline, nortriptyline and imipramine were substantially more potent in the inhibition of noradrenaline-induced intracellular Ca(2+) increases in HEK-293 cells expressing alpha(1A)- or a truncated version of alpha(1D)-adrenoceptors which traffics more efficiently towards the cell membrane than in cells expressing alpha(1B)-adrenoceptors. Amitriptyline, nortriptyline and imipramine are much weaker antagonists of rat and human alpha(1B)-adrenoceptors than of alpha(1A)- and alpha(1D)-adrenoceptors. The differential affinities for these receptors indicate that the alpha(1)-adrenoceptor subtype which activation is most increased by the augmented noradrenaline availability resultant from the blockade of neuronal reuptake is the alpha(1B)-adrenoceptor. This may be important for the behavioural effects of these drugs. Copyright 2010 Elsevier Ltd. All rights reserved.

Citation

F D Nojimoto, A Mueller, F Hebeler-Barbosa, J Akinaga, V Lima, L R de A Kiguti, A S Pupo. The tricyclic antidepressants amitriptyline, nortriptyline and imipramine are weak antagonists of human and rat alpha1B-adrenoceptors. Neuropharmacology. 2010 Jul-Aug;59(1-2):49-57