Effect of dobutamine, a new cardioselective sympathomimetic drug, on myocardial oxygen balance in conscious dogs

The effects of (+/-)-4-(2-3-(p-hydroxyphenyl)-1-methylpropyl]-amino)-ethyl-pyrocatechol hydrochloride (dobutamine) on myocardial O2 balance were investigated in healthy conscious dogs with experimental AV-block. Dobutamine, injected as a bolus of 3, 6, 10 micrograms/kg, increased myocardial contractility, coronary flow, coronary venous O2 saturation and aortic pressure, while initially decreasing SA-node rate. Following ganglionic blockade the effects of dobutamine on myocardial contractility were unchanged while those on coronary flow and coronary venous O2 saturation were reduced by 30%. Aortic pressure and heart rate showed a dose dependent, long-lasting increase. The effects of dobutamine on heart rate and myocardial contractility could be abolished by beta 1-adrenoceptor blockade with practolol (2 mg/kg) while the effects on coronary flow and myocardial O2 extraction were reduced by 40% after practolol. Following beta 1 + 2 adrenoceptor blockade with propranolol, dobutamine increased aortic pressure and coronary flow while coronary resistance and myocardial oxygen extraction were unaffected.