Positive inotropic and chronotropic effects of pancuronium and vecuronium in the canine blood-pefused papillary muscle and sinoatrial node preparations.

The positive inotropic and chronotropic potencies of pancuronium (Pc) and vecuronium (Vc) were compared with developed tension of the isolated papillary muscle (DT) and sinoatrial rate of the sinoatrial node preparation (SAR). Both Pc and Vc caused dose-dependent positive inotropic and chronotropic effects. Pc showed much more potent effect than Vc on DT (0.1, 0.3 mg; P << 0.05) or SAR (0.03, 0.1, 0.3 mg; P << 0.05). DT and SAR were increased by Pc and Vc, and the increase in DT was inhibited by propranolol or tetrodotoxin. These results suggest that the cardiac effects of Pc or Vc may be mediated by release of norepinephrine from the synpathetic nerve endings.