Absence of vasoactive and cardiotropic substances in coronary sinus blood of dogs.

Elucidation of the mechanism by which coronary flow is regulated has been attempted. Substances with coronary vasodilator or vasoconstrictor properties as well as those with inotropic or chronotropic effects on isolated frog hearts were sought in the coronary sinus blood of dogs. Blood draining normal, hypoxic or "overperfused" hearts was oxygenated in a dog lung or on a screen and perfused at a controlled pressure through a rotameter into a test coronary artery of the same or second dog; unoxygenated sinus blood was also perfused into an isolated beating frog heart connected to record heart rate and amplitude of contraction. No significant differences in flow rates were observed when the test artery was perfused with oxygenated coronary sinus blood as compared to flows metered during perfusion of the artery with arterial blood. Similarly, perfusion of unoxygenated coronary sinus blood into the isolated frog heart did not affect the rate or amplitude of contraction recorded during perfusion of the heart with arterial blood. These experiments, therefore, failed to demonstrate substances having vasoactive, inotropic, or chronotropic properties in the blood draining normal, hypoxic or "overperfused" dog hearts.