Abstract
Protective effects of β-blockers (oxprenolol, propranolol and carteolol) on the abnormal ECG of the sympathicotonia type were studied in male ddY SART stressed mice. Oxprenolol and carteolol were observed to have mild effects on the abnormal ECG as compared with propranolol. Experimental arrhythmias were induced by drugs in SART mice, and their frequencies of appearance were examined. The types of arrhythmias used as indices were sinus arrhythmia, supraventricular and ventricular extrasystole, the 1st and 2nd degrees of atrio-ventricular (A-V) block, sino-atrial (S-A) block and sinus standstill. The frequency of appearance of arrhythmia of any type induced by adrenaline was lower in SART mice than in normal mice. The frequency of appearance of methacholine (MCh)-induced arrhythmia of any type was significantly higher in SART mice than in normal mice. Protective effects of the 3 β-blockers on the worsening of MCh-arrhythmias in SART mice were studied. With a single dose of 5 or 10 mg/kg, the drugs were effective on supraventricular extrasystole and S-A block. Continuous administrations of oxprenolol and carteolol inhibited the occurrence of supraventricular extrasystole, A-V block and S-A block, but not the occurrence of ventricular extrasystole. Continuous administrations of propranolol were effective on any type of arrhythmias except for sinus arrhythmia. These results further support our viewpoint that the SART mouse is of the sympathicotonia type with respect to the heart, and they suggest that oxprenolol and carteolol may be effective clinically on arrhythmias caused by autonomic imbalance.
