HIGH-LEVELS OF ASCORBIC-ACID, NOT GLUTATHIONE, IN THE CNS OF ANOXIA-TOLERANT REPTILES CONTRASTED WITH LEVELS IN ANOXIA-INTOLERANT SPECIES

Ascorbic acid and glutathione (GSH) are antioxidants and free radical scavengers that provide the first line of defense against oxidative da mage in the CNS. Using HPLC with electrochemical detection, we determi ned tissue contents of these antioxidants in brain and spinal cord in species with varying abilities to tolerate anoxia, including anoxia-to lerant pond and box turtles, moderately tolerant: garter snakes, anoxi a-intolerant clawed frogs (Xenopus laevis), and intolerant Long-Evans hooded rats. These data were compared with ascorbate and GSH levels in selected regions of guinea pig CNS, human cortex,and values from the literature. Ascorbate levels in turtles were typically 100% higher tha n those in rat. Cortex, olfactory bulb, and dorsal ventricular ridge h ad the highest content in turtle, 5-6 mu mol g(-1) of tissue wet weigh t, which was twice that in rat cortex (2.82 +/- 0.05 mu mol g(-1)) and threefold greater than in guinea pig cortex (1.71 +/- 0.03 mu mol g(- 1)). Regionally distinct levels (2-4 mu mol g(-1)) were found in turtl e cerebellum, optic lobe, brainstem, and spinal cord, with a decreasin g anterior-to-posterior gradient. Ascorbate was lowest in white matter (optic nerve) in each species. Snake cortex and brainstem had signifi cantly higher ascorbate levels than in rat or guinea pig, although oth er regions had comparable or lower levels. Frog ascorbate was generall y in an intermediate range between that in rat and guinea pig. In cont rast to ascorbate, GSH levels in anoxia-tolerant turtles, 2-3 mu mol g (-1) Of tissue wet weight, were similar to those in mammalian or amphi bian brain with no consistent pattern associated with anoxia tolerance . GSH levels in pond turtle CNS were significantly higher(by 10-20%) t han in rat for several regions but were generally lower than in guinea pig or frog. GSH in box turtle and snake CNS were the same or lower t han in rat or guinea pig. The distribution GSH in the CNS also had a d ecreasing anterior-to-posterior gradient but with less variability tha n ascorbate: levels were similar in optic nerve, brainstem, and spinal cord. The paradoxically high levels of ascorbate in turtle brain, whi ch has a lower rate of oxidative metabolism than mammalian, suggest th at ascorbate is an essential cerebral antioxidant. High levels may Rav e evolved to protect cells from oxidative damage when aerobic metaboli sm resumes after a hypoxic dive.