The effect of
ortho-iodo sodium benzoate (
OISB) on the
oxyhemoglobin dissociation curve of coronary venous blood was studied in an isolated canine heart preparation perfused at a constant coronary blood flow. Changes in P-50 (millimeters of
mercury) [the
oxygen tension (pO2) at which
hemoglobin is 50% saturated], were used to express
hemoglobin-
oxygen affinity. Intracoronary infusion of
OISB (200, 400 and 800 mg/min) produced a dose-related increase in coronary venous P-50 and a concurrent increase in coronary venous pO2. In addition,
OISB produced a significant decrease in heart rate and increase in coronary artery perfusion pressure. During cardiac pacing at 150, 190 and 230 beats/min,
OISB (400 mg/min) significantly increased coronary venous P-50, myocardial
oxygen exrraction (O2E) and oxygen consumption (MVO2) whereas coronary venous PO2 was not changed. Furthermore, a 5-minute intracoronary infusion of
OISB (200 mg/min) during
myocardial ischemia produced an increase in O2E, MVO2 and myocardial contractility with little change in coronary venous pO2. These results suggest that acute pharmacological manipulation of the
oxyhemoglobin dissociation curve may enhance
oxygen release to the myocardium while maintaining the effective driving pressure (as reflected in coronary venous pO2) for diffusion of
oxygen to the myocardium.