OXIDATIVE DAMAGE AND ANTIOXIDANTS IN RANA-SYLVATICA THE FREEZE-TOLERANT WOOD FROG

Freeze-tolerant wood frogs (Rana sylvatica) must endure prolonged isch emia on freezing. Reperfusion on thawing brings with it the potential for oxidative damage due to reactive oxygen species formation, a well- known consequence of mammalian ischemia-reperfusion. To determine whet her oxidative damage occurs during thawing and how frogs deal with thi s, we examined oxidative damage and antioxidant and prooxidant systems in tissues of Rana sylvatica and a nonfreezing relative, Rana pipiens . Glutathione status indicated little oxidative stress in tissues duri ng freezing or thawing; an increase of the glutathione pool in the oxi dized form was observed during freezing only in Rana sylvatica kidney (by 85%) and brain (by 33%). Oxidative damage to tissue lipids, measur ed as the levels of thiobarbituric acid-reactive substances and/or by an Fe(III)xylenol orange assay, did not increase above control values over a freeze-thaw time course. Correlative data showing increased act ivities of some antioxidant enzymes during freezing, notably glutathio ne peroxidase (increasing 1.2- to 2.5-fold), as well as constitutively higher activities of antioxidant enzymes and higher levels of glutath ione in the freeze-tolerant species compared with Rana pipiens, sugges t that antioxidant defenses play a key role in amphibian freeze tolera nce.