Effect of propranolol and nitroglycerin on hemoglobin--oxygen affinity

The effect of propranolol on the oxyhemoglobin dissociation curve (P-50) of coronary venous blood was studied in isolated canine hearts. I.v. administration of propranolol (0.5, 5.0 mg/kg) produced no significant change in P-50 over 4 hr. Following propranolol, an intracoronary infusion of nitroglycerin (10 mug/min) increased P-50. Addition of propranolol (5 X 10(-5) M to 1 X 10(-4)M) to central venous blood in vitro produced a significant increase in P-50. These data indicate that propranolol increases P-50 in vitro but does not increase P-50 in vivo, whereas nitroglycerin increases P-50 In vivo but not in vitro.