Coronary flow in heart-lung preparation affected by cardiopulmonary nerves and arterial PCO2

Studies on coronary vasodilator drugs utilizing heart-lung preparations (HLP) have been disturbed by a spontaneous gradual increase in coronary blood flow. With the purpose of finding out what would cause the gradual increase, the time course of coronary sinus blood flow (CSBF) was investigated in 20 dog HLPs under four experimental conditions, according to whether cardiopulmonary nerves (CPN) were severed or not and whether CO2 content in the inspiratory gas was high (95% O2-5% CO2) or low (50% O2-50% room air). The gradual increase in CSBF was observed, accompanied by a significant increase in 6-ketoprostaglandin F1 alpha in the arterial blood, only when CPN were intact and, simultaneously, inspiratory CO2 was high. Nevertheless, the hemodynamic parameters, except CSBF, were almost similar under four conditions. These results suggested that CSBF in HLP could be affected via a synthesis and/or a release of prostaglandin I2 by the interaction of CPN and arterial PCO2.