Alterations of glucose metabolism during perfusion of rat lung with paraquat

Isolated perfused rat lungs were used to investigate effects of paraquat on lung glucose metabolism. Lungs were ventilated with 5% CO2 in air and perfused with Krebs-Ringer bicarbonate buffer, pH 7.4, containing albumin and 5.5 mM radiolabeled D-glucose. Control lung glucose utilization, estimated from rate of 3H2O production from [5-3H]glucose, was 44 mumol/h-g dry wt. Pentose cycle activity, based on 14CO2 specific yields at the end of perfusions with [1-14C]- and [6-14C]glucose, was 14% of glucose utilization. During perfusion with 1.5 mM paraquat, glucose utilization increased 28%, 14CO2 production via the pentose cycle increased 182% (P less than 0.005), CO2 production via mitochondrial metabolism increased 39% (P less than 0.02), and the rate of lactate production increased 28% (P less than 0.05). Pyruvate production and the lactate-to-pyruvate ratio were not significantly altered. The data indicate that interaction of paraquat with the lung results in increased turnover of cytoplasmic NADPH and increased mitochondrial metabolism, but no significant change in cytoplasmic redox state. The findings are compatible with intracellular enzymatic reduction of paraquat by an NADPH-requiring reductase.