Increase in production of ascorbate radical in tissues of rat treated with paraquat

The production of ascorbate radical (A^·-) was investigated in tissues of rats intoxicated with paraquat (PQ) to know the protective role of antioxidant ascorbate (AH^·-) in tissues. The electron spin resonance (ESR) method is applied to observe A^·-. To eliminate increased biosynthesis of ascorbic acid (AH₂) by PQ intoxication, ODS rats were chosen and fed with or without 250 ppm PQ in the diet. The radical A^·- was detected only in the lung and spleen homogenates of both intoxicated and control rats at the beginning of ESR measurement. The radical levels of intoxicated rat lung and spleen were increased rapidly to twice the initial level after 3 h and decreased to 0.2–0.6 times the initial level after 24 h, whereas those of control rats were increased slowly to 1.1 times the initial level after 4 h and decreased slowly to 0.7 times the initial level after 24 h at 4°C. In other organs such as liver, kidney, heart and testis, A^·- was not detected initially but detected afterwards. Higher A^·- level was observed in the intoxicated rat liver than the control but no appreciable differences of A^·- levels were observed between the intoxicated kidney, heart and testis and the respective controls. In the intoxicated rat lung the concentration of AH₂ is only half but that of A^·- is twice as high as that of the control. Larger amounts of A^·- produced in the intoxicated rats decayed more quickly than those in the control rats. The simple addition of PQ to the control organ enhanced neither A^·- production nor A^·- quenching. These facts suggest that the tissues damaged by PQ require larger amounts of AH^- to detoxicate harmful oxidants, resulting in concomitant production of A^·-.