Seasonal variations in the antioxidant defence systems and lipid peroxidation of the digestive gland of mussels.

1. The seasonal variations in the level of antioxidant compounds (glutathione (GSH), vitamin E, carotenoids) and in the activity of antioxidant enzymes, superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), GSH-peroxidase (EC 1.11.1.9) in the digestive gland of mussels (Mytilus sp.) were evaluated. The lipid peroxidation process was also measured by determining the tissue concentration of malondialdehyde (MDA). 2. The physiological fluctuations of the antioxidant defence systems were inversely related to the accumulation of lipid peroxidation products (MDA) in the tissue. The observed seasonal variations are presumably related to the changing metabolic status of the animals, itself dependent on such factors as gonad ripening and food availability. 3. In particular, the obtained data indicate that a reduction of the antioxidant defence systems, occurring during winter, could be directly responsible for an enhanced susceptibility of mussels tissues to oxidative stress, as indicated by the high MDA concentration observed in this period.