Adenosine export from the liver: oxygen dependency.

The liver is believed to be an important regulator of purine concentrations in the circulation. It has been an accepted notion that the liver exports the riboside adenosine to the circulation for use by other tissues. This phenomenon was reexamined using an artificial oxygen carrier to perfuse the isolated rat liver and high-performance liquid chromatography (HPLC) to analyze the purine content. It was found that perfusion with Krebs-Ringer-bicarbonate at a physiological flow rate as had been used by previous investigators results in a mildly hypoxic preparation, and it is this hypoxia that results in the export of adenosine. In a liver perfused with Fluosol-43, little (less than 0.05 microM) or no adenosine was released. However, if the oxygen content of Fluosol-43 was decreased, the liver could be induced to release adenosine at 1.0 microM levels. In addition, the liver was found to release adenine under control conditions; thus it is this purine base that is likely to be the important purine released by the liver for extrahepatic salvage, not adenosine as previously thought.