Use of an artificial oxygen carrier in isolated rat liver perfusion: first demonstration of net glucose uptake at physiological portal glucose concentrations using a hemoglobin-free perfusate

Summary

A defect in isolated perfused rat-liver (IPRL) preparations has been proposed to explain discrepancies between in vivo and in vitro findings regarding hepatic glucose metabolism. The aim of the present study was to investigate whether a preparation of IPRL using a synthetic hemoglobin-free perfusate was capable of net glucose uptake and glycogen deposition at physiological portal substrate concentrations. Livers from fed anaesthetized rats were perfused in a recirculating system using a fluorocarbon emulsion as artificial oxygen carrier. Depending on the prevailing glucose concentration, livers exhibited net glucose uptake or release with a threshold value of 5.5–6.0 mM glucose. Net glucose uptake was associated with net glycogen deposition (+0.23 to +0.59 μmol C₆ min⁻¹g⁻¹). From 5.8 mM (n=3) and 10.0 mM (n=8), initial concentration glucose levels fell to 5.3±0.2 mM after 210 min (n=3) and 6.3±0.9 mM after 120 min (n=8), respectively. This was equivalent to a net glucose uptake of −0.16 and −0.45 μmol min⁻¹g⁻¹. Anoxia reversibly switched hepatic glucose balance from net uptake (−0.42 μmol min⁻¹g⁻¹) to release (+0.69 μmol min⁻¹g⁻¹) followed by net uptake (−0.50 μmol min⁻¹g⁻¹) after reinstitution of aerobic conditions.

We conclude that the composition of perfusion media might play a pivotal role for studies of glucose metabolism in the isolated perfused rat liver. In our experimental model, using a hemoglobin-free synthetic medium, net glucose uptake was readily demonstrated at physiological portal substrate concentrations similar to the in vivo situation.