Haemodynamic effects of the beta-receptor blocking agents metoprolol and propranolol in the anesthetized dog

The haemodynamic effects produced by intravenous infusions of the beta-blocking agents metoprolol and propranolol in doses of 0.3 and 1 mg/kg/10 min were compared in anaesthetized dogs. When administered in a dose of 0.3 mg/kg/10 min, metoprolol caused a longer-lasting increase in pulmonary-arterial pressure and total pulmonary resistance, a greater increase in pulmonary capillary pressure and a more marked decrease in O2 partial pressure in the arterial blood than propranolol. These differences are probably due to differences in the pharmacokinetics of the two drugs. The effects of the two beta-blockers in a dose of 1 mg/kg/10 min were similar. At neither of the dose-levels tested were the changes induced by the compounds in the various parameters studied clearly dose-related.