Effects of bunitrolol on myocardial contractility and left ventricular myosin isoenzyme pattern.

Effects of long term treatment of hypertension with bunitrolol on myocardial contractility and left ventricular myosin isoenzyme pattern were examined. Male 22-week-old spontaneously hypertensive rats were treated with bunitrolol (30-40 mg/kg/d, p.o.) for 8-10 weeks. The blood pressure of the bunitrolol-treated group did not differ from that of the untreated group, but ratio of ventricular weight to body weight was significantly lower in the treated group. There were no significant differences in isometric developed tension and dT/dtmax of isolated left ventricular papillary muscles between bunitrolol-treated and control groups. Myocardial mechanical responses to isoprenaline (isoproterenol) also showed no differences between the two groups. Left ventricular myosin isoenzyme pattern obtained by pyrophosphate gel electrophoresis was significantly shifted to VM-1 by bunitrolol treatment.