Effects of ischaemia and reperfusion on NADH coenzyme Q reductase activity in rat liver

NADH coenzyme Q reductase (EC 1.6.5.3) has been suggested in the literature to be inactivated by ischaemia. In the present study, NADH coenzyme Q reductase activity was localized in unfixed cryostat sections of ischaemic rat livers and quantified using image analysis. In vitro ischaemia was induced by storage of rat liver fragments for 30, 60, and 120 min at 37 degrees C. In vivo ischaemia was provoked by clamping the afferent vessels of median and left lateral liver lobes for 60 min followed by 30, 60 and 180 min of reperfusion. NADH coenzyme Q reductase activity was demonstrated with the tetrazolium salt method in the presence of polyvinyl alcohol. Final reaction product was found in liver parenchymal cells and its distribution was homogeneous within liver lobules. Only low amounts of final reaction product were formed when the incubation was performed in the absence of the substrate NADH. A non-linear relation was found between the absorbance and incubation time when the reaction was performed in the presence of NADH. Therefore, the initial velocity was taken as the true rate of enzyme activity. A linear relationship was found for the initial velocity and section thickness up to 6 microm followed by a levelling off. Electron microscopically, NADH coenzyme Q reductase activity was localized at the outer and inner membranes of mitochondria. In vitro ischaemia up to 120 min did not affect NADH coenzyme Q reductase activity. At 30 min reperfusion after in vivo ischaemia for 60 min enzyme activity was slightly decreased in certain foci which also showed diminished lactate dehydrogenase activity. A further decrease of enzyme activities in foci was observed at 180 min reperfusion after ischaemia. It is concluded that NADH coenzyme Q reductase activity is not sensitive to ischaemia. Furthermore, it is likely that the enzyme leaks from liver parenchymal cells into the circulation during reperfusion after ischaemia.