ANTIOXIDANT DEFENSES AND LIPID-PEROXIDATION DURING ANOXIA STRESS AND AEROBIC RECOVERY IN THE MARINE GASTROPOD LITTORINA-LITTOREA

The effect of anoxia exposure (6 days under N-2 gas at 5 degrees C) an d aerobic recovery (at 5 degrees C) on the antioxidant defenses of the marine periwinkle, Littorina littorea L., were assessed in hepatopanc reas and foot muscle. In hepatopancreas, the maximal activities of ant ioxidant enzymes clearly responded to changes in oxygen availability. Activities of five enzymes were suppressed (to 44-70% of controls) in hepatopancreas during anoxia exposure: superoxide dismutase (SOD), cat alase (CAT), total glutathione peroxidase (GPox), glutathione reductas e (GR) and glutathione-S-transferase. When returned to aerobic conditi ons, activities of the glutathione-related enzymes in hepatopancreas a ll rose again in concert reestablishing control levels within 12 h, wh ereas SOD and CAT activities remained suppressed even after 24 h recov ery. In foot muscle only SOD activity decreased during anoxia (to 56% of control), whereas, during aerobic recovery, GPox activity decreased by about 85%, and SOD, CAT and GR activities rose. Anoxia exposure st imulated an increase in the amount of the low molecular weight antioxi dant, glutathione, in both organs; total glutathione (GSH + 2GSSG) was 2.8- and 1.6-fold higher than control levels in hepatopancreas and fo ot, respectively. Elevated GSH may be needed when oxygen is reintroduc ed or synthesis of the tripeptide may be favored under the reducing co nditions of anoxia. Total glutathione content of both tissues continue d to rise during aerobic recovery but only after 24 h recovery did a s ignificant increase in the GSH/GSSG ratio occur. The changes in enzyma tic and metabolite antioxidant defenses during anoxia and recovery sug gest that these are naturally adaptable in response to changes (or ant icipated changes) in the generation of oxygen free radicals within tis sues, a feature that could serve the natural lifestyle of this species which experiences cyclic periods of oxygen availability/deprivation w ith the changing tides. To determine whether antioxidant defenses were responding to free radical damage to tissue macromolecules, peroxidat ive damage to lipids was also measured by three methods that quantify damage at different stages of lipid degradation: initial (conjugated d ienes), middle (lipid hydroperoxides), and terminal (thiobarbituric ac id reactive substances (TEARS) measure breakdown products such as malo ndialdehyde). Hepatopancreas showed no change in either initial or ter minal products of radical attack over anoxia/recovery (6 days of anoxi a followed by 0.5, 1, 5 or 12 h aerobic recovery), whereas the level o f lipid hydroperoxides was strongly suppressed during anoxia and remai ned low throughout recovery. Thus, the antioxidant defenses of hepatop ancreas appear to be fully capable of handling an increase in oxygen f ree radical generation associated with the reintroduction of oxygen af ter anoxia. Foot muscle showed a different response with increased dam age detected at both initial and middle stages during anoxia exposure. However, lipid hydroperoxide levels were reduced again within 30 min of recovery, whereas levels of conjugated dienes returned to control v alues after 5 h. TEARS were largely unaffected in foot suggesting that peroxidative damage can be repaired in the tissue so that terminal br eakdown products do not accumulate. (C) 1998 Elsevier Science B.V.