ANTIOXIDANT DEFENSES AND LIPID-PEROXIDATION DAMAGE IN ESTIVATING TOADS, SCAPHIOPUS-COUCHII

Tissue-specific changes in antioxidant defenses and lipid peroxidation damage were analyzed in spade-foot toads. Scaphiopus couchii, to dete rmine how these responded during estivation, a state of suppressed oxy gen consumption. Maximal activities of glutathione-S-transferase, glut athione reductase, glutathione peroxidase, superoxide dismutase and ca talase were measured in sis organs from 3-month-estivated toads and co mpared with activities in animals awakened for 10 days after estivatio n. Activities of many enzymes, particularly the glutathione-linked enz ymes, were significantly lower in tissues of estivating toads than in awake toads, This indicates that enzymatic antioxidant defenses are pr obably modulated in response to the rate of reactive oxygen species ge neration in tissues, which is proportional to oxygen consumption. Anti oxidant enzyme activities were largely insensitive to high urea, which accumulates during estivation-but were inhibited by elevated KCI. Lev els of reduced glutathione were also significantly lower in three orga ns during estivation and all organs, except skeletal muscle, exhibited a higher oxidized/reduced glutathione ratio, indicating a more oxidiz ed state during estivation. Products of lipid peroxidation (conjugated dienes, lipid hydroperoxides) were higher in tissues of estivated tha n control toads, suggesting accumulated oxidative damage to lipids dur ing dormancy. One enzymatic source of free radical generation, xanthin e oxidase, appeared to have little impact because its activity was del ectable only in liver and was significantly lower in estivated toads. The data indicate that both enzymatic and metabolite antioxidant defen ses in toads are adaptable systems that are modulated in estivating ve rsus awake states.