Effect of propafenone hydrochloride on lymphocyte membrane beta(sub-2) adrenoceptors in ventricular arrhythmias

Propafenone is a new anti-arrhythmic drug that is used to stabilize the heart beat of individuals who experience irregularities of the heart's conduction system. The action of the drug is complex and it is reported to have effects which can both reduce the heart rate and decrease blood pressure by apparently blocking receptors on the heart muscle. In this action the drug is blocking the physiologic action of epinephrine-like compounds which are produced, for example, by the adrenal glands. When used as an anti-arrhythmic, propafenone is used at a dosage level that is approximately 50 times higher than that used for propranolol, a potent beta-blocker, making propafenone's effect as a beta-blocker extremely important. Beta-blockers are also reported to cause an 'up-regulation' in receptors for beta-adrenergic compounds on target cells. In this study the ability of propafenone to cause such an up-regulation on specific white blood cells of patients taking the drug was examined. Propafenone was able to increase by approximately 90 percent the density of beta-adrenergic receptors on lymphocytes, yet its action to perform as a beta-blocker was only modest. The results suggest that the effect of beta-blockers is best tested by studying the heart during exercise. This new medication may be important in cases where there is arrhythmia and impaired cardiac function; however, additional clinical trials will be necessary to clarify this concept.