Assessment of vasoactive metabolites released from the isolated guinea pig during heart hypoxia and beta-adrenergic stimulation.

Two isolated guinea pig hearts (H1, H2) were perfused in series in order to bioassay in the recipient heart (H2) the release of vasoactive metabolites. Due to an effective reoxygenation system transit time between H1 and H2 as only 20 sec. Hypoxic perfusion (30% O2) of H1 caused relaxation of the coronary vessels of H2, and this effect could be completely abolished by adenosine deaminase. Similar results were obtained when H1 was stimulated by isoproterenol while H2 was protected by propranolol. From our findings it is concluded that adenosine is the primary vasodilating substance released by the heart into the coronary circulation.