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Pharmacological and antiarrhythmic properties of quinacainol : a new sodium channel blocker?

University of British Columbia

Quinacainol, 1-[2-(1,1-dimethylethyl)-4-quinolyl]-3-(4-piperidyl)-1-propanol is a class I antiarrhythmic agent provisionally subclassified as Ic. Studies were carried out in order to (1) determine the actions of quinacainol in acute myocardial ischæmia, (2) ascertain the mechanism(s) responsible for these actions, and (3) ascertain the appropriateness of its subclassification. Toxicological, hæmodynamic, and ECG effects in chronically prepared conscious rats were determined following administration of 1, 2, 4, or 8 mg/kg of quinacainol given i.v. over 10 minutes on alternate days. Toxicity referable to the heart was seen at doses of 8 mg/kg and above. In rats given 8 or 16 mgkg, arrhythmias occurred. Quinacainol had no major effects on blood pressure, unlike most class I antiarrhythmics, but lowered heart rate (not statistically significantly) and prolonged P-R interval and QRS duration. In an attempt to protect against ischæmic arrhythmias, doses of 2 mg/kg and 4 mg/kg were given. The high dose gave the best protection. It reduced the incidence of ventricular tachycardia (VT) from a control value of 80% to 30%, and reduced the incidence of ventricular fibrillation (VF) from a control value of 60% to 10%. An increase in the incidence of premature ventricular contractions was seen at both doses. Blood pressure was not adversely effected although slight bradycardic effects as well as prolongation of the P-R interval were seen at both doses. Both doses reduced S-T segment and delayed onset of elevation of S-T segment and R-wave which were induced by coronary occlusion. Sensitivity to electrical stimulation was tested in pentobarbital anæsthetised rats using ventricular electrodes. Doses of 0.5, 1, 2, and 4 mg/kg were given cumulatively as a 10 min infusion every 25 min. Quinacainol did not affect QRS duration or the Q-Tc interval but dose-dependently widened P-R interval when compared to pretreatment. Quinacainol dose-dependently increased threshold current, threshold duration, and ventricular fibrillation threshold. In addition, quinacainol elevated effective refractory period while decreasing maximum following frequency. Open-chest rats under pentobarbital anæsthesia were used to record the effects of quinacainol on epicardial intracellular potentials. Recordings were made by conventional microelectrode techniques before and after cumulative doses of 0.5, 1, 2, 4, and 8 mg/kg i.v. Quinacainol dose-dependently reduced phase zero of the action potential (AP) and AP height but did not influence other phases of the AP (with the exception of prolonging repolarization at the highest dose); actions indicative of class Ic. Effects of quinacainol on isolated rat hearts were assessed using a modified Langendorff heart preparation and were compared with those of tetrodotoxin (TTX). Quinacainol widened the P-R interval and QRS duration without having major effect on the Q-Tc interval. In addition it slowed the sinus beating rate. Quinacainol was more potent than TTX. All findings indicated that quinacainol is a potent antiarrhythmic agent with Na⁺channel blocking properties.

Text

2010-10-04

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http://hdl.handle.net/2429/28911

Pharmacology

University of British Columbia

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