Measurements of oxygen tension in perfusates from guinea pig isolated hearts and the demonstration of coronary vasodilator material.

The release of coronary vasodilator mediator(s) from guinea pig isolated hearts was demonstrated by a technique employing donor and recipient hearts perfused in series. Vasodilator mediator release followed the positive inotropic, chronotropic, and coronary vasodilator responses of donor hearts to isoprenaline and their exposure to hypoxia. Isoprenaline-induced coronary vasodilatation of donor hearts was accompanied by a fall in perfusate pO2, indicative of a raised myocardial oxygen consumption. Measurement of perfusate pO2 levels showed that the regassing procedure was adequate and the fall in pO2 level no longer occurred after isoprenaline. However, at high resolution, small changes in pO2 could still be detected by these were not sufficient to induce vasodilatation of the recipient. The technique was adapted to enable simultaneous measurement of perfusate pO2 and release of vasodilator mediator following administration of isoprenaline. The value of this in examining the relationship between myocardial oxygen consumption and vasodilator mediator release is discussed.