Ascorbate distribution during hibernation is independent of ascorbate redox state

Abstract

Distribution of ascorbate into tissues is an essential process in ascorbate antioxidant defense. Hibernating animals are studied as a model of tolerance to ischemia–reperfusion because of their tolerance to fluctuations in blood flow associated with prolonged torpor and periodic arousal episodes. Throughout hibernation, plasma ascorbate concentration ([Asc] p ) repetitively increases during torpor, then falls during periodic arousal bouts. We previously proposed that high [Asc] p provides a ready source of antioxidant protection for distribution to the central nervous system and peripheral tissues during arousal. Here we tested whether deliberate oxidation of plasma ascorbate by intravenous administration of ascorbate oxidase (AO), prior to arousal, compromised tissue levels of ascorbate or the other water-soluble antioxidants, glutathione (GSH) and urate. Although AO decreased [Asc] p to below the level of detection during torpor and after arousal, ascorbate oxidation did not decrease post-arousal tissue levels of reduced ascorbate, glutathione, or urate in any tissue examined, except liver. The data imply that ascorbate is taken up equally well into brain and other tissues as either ascorbate or its oxidized product dehydroascorbate, with subsequent intracellular reduction of dehydroascorbate. Lack of effect of ascorbate oxidation on tissue levels of GSH or urate indicates that dehydroascorbate uptake and reduction do not compromise tissue concentrations of these other water-soluble antioxidants. Thus, we show equal availability of reduced and oxidized plasma ascorbate during metabolically demanding thermogenesis and reperfusion associated with arousal from hibernation.