The liver is an organ site for the release of inosine metabolized by non-glycolytic pig red cells

Abstract

The metabolic energy source used by the pig red cell, which is unable to metabolize blood-borne glucose, was examined. Potential physiological substrates include adenosine, inosine, ribose, deoxyribose, dihydroxyacetone and glyceraldehyde, of which inosine was previously implicated. A net ATP synthesis by red cells occurs during in situ perfusion through the adult miniature pig liver. HPLC analysis of the perfusate revealed the presence primarily of inosine and hypoxanthine. Inosine production by the liver was 0.015 μmol/g per min. Moreover, red cells maintain ATP when suspended in a balanced salt medium during a 6 h incubation at 38°C, in which inosine is continuously infused to give an external concentration of no more than 3 μmol/l, mimicking its plasma level. Inosine consumption under these infusion conditions was 56 nmol/ml cell per h, which is two orders of magnitude lower than when inosine is present in millimolar concentration. The total red cell inosine consumption of 9.63 μmol/h is much less than the total liver inosine production of 212 μmol/h. These findings suggest that the liver is an organ site elaborating inosine, and that maintenance of a 3 μmol/l inosine in plasma is sufficient to meet the energy requirements of the pig red cells.