Akrinor-induced relaxation of pig coronary artery in vitro is transformed into α₁-adrenoreceptor-mediated contraction by pretreatment with propranolol

Akrinor (AKR), a mixture of theodrenaline (TDR) and cafedrine (CDR), is a sympathomimetic agent used to counter transitory hypotension. Although some cases of vascular complications associated with AKR have been reported there are no experimental data about its direct effects on coronary arteries. The effects of AKR, TDR, CDR, and ephedrine (EDR) were studied on the isometric contraction of the ring preparations of pig coronary arteries precontracted with KCl. The influence of endothelium removal and preincubation with nonselective β-adrenoreceptor antagonist propranolol (PROP), α1-adrenoreceptor antagonist prazosin, dopamine receptor antagonist SCH 23390, and adenosine receptor antagonist CGS 15943 were also tested. AKR, TDR, and CDR produced relaxation of the preparations. Preparations without endothelium were more sensitive to AKR relaxing effects. EDR produced an increase of vascular ring tonus. AKR, TDR, and EDR produced contraction in preparations pretreated with PROP. Higher concentrations of AKR relaxed PROP-pretreated preparations. AKR-induced contraction could be prevented by pretreatment with prazosin. Dopamine and adenosine receptor antagonists did not influence relaxing effects of AKR. In conclusion, AKR and its constituents induce the relaxation of pig coronary artery preparations precontracted with KCl. The observed contraction in the preparations pretreated with PROP was probably due to stimulation of unmasked α1-adrenoreceptors.