Evidence that activation of Kupffer cells increases oxygen uptake after cold storage

Fasting for long periods of time has previously been shown to increase survival following liver transplantation. The experiments reported here were designed to study the mechanism of this phenomenon. Livers stored in cold Euro-Collins solution for 16 hr were perfused subsequently for 3 hr. Oxygen uptake increased slowly, reaching maximal values after about 80 min of reperfusion. This increase in oxygen uptake was significantly greater in livers from fed rats (73 mumol/g/hr) than in livers from either 4-day fasted rats (42 mumol/g/hr) or from rats where Kupffer cells were inactivated by gadolinium chloride treatment (30 mumol/g/hr). Thus, it is likely that the increase in oxygen uptake involves activation of Kupffer cells on reperfusion. Therefore, carbon uptake, which is due predominantly to phagocytosis by Kupffer cells, was monitored in the perfused liver. Carbon uptake was increased significantly in livers from fed rats at 80 compared with 20 min of perfusion. Further, carbon uptake was diminished significantly by long-term fasting and gadolinium chloride treatment. These results indicate that oxygen uptake increases in parallel with activation of Kupffer cells in livers from fed rats and support the hypothesis that activated Kupffer cells produce factors that stimulate oxygen uptake after cold storage. In further support of this hypothesis, the observed increase in oxygen uptake was diminished when the flow rate was increased. Because mediators would be diluted as the flow rate was increased, this result is consistent with the hypothesis that oxygen uptake depends on chemical mediators released from Kupffer cells. When livers were perfused with indomethacin, a prostaglandin synthesis inhibitor, the increase in oxygen uptake observed in fed rats was reduced by 34%. Further, in livers perfused under hypoxic conditions using a low-flow model, lactate dehydrogenase release in livers from fed rats (547 U/g/hr) was significantly greater than in livers from 4-day fasted rats (397 U/g/hr), indicating that fasting increased tolerance to hypoxia. In conclusion, livers of fasted rats require less oxygen during reperfusion, most likely because activation of Kupffer cells on reperfusion is minimized. These findings could explain why survival after transplantation is improved by long-term fasting.