Does relaxation as a sedative therapy previous to pearl production affect antioxidant response and cause oxidative damage in the winged pearl oyster Pteria sterna?

Relaxation as a sedative therapy before nucleus seeding is assumed to be stressful to some marine animals during its initial phase, before acting at the cellular level. The antioxidant activity and possible oxidative damage to soft tissues was evaluated in the winged pearl oyster Pteria sterna exposed to four relaxants, at two concentrations each. The relaxants were: propylene phenoxetol (1.5 and 2.5 mL L-1), benzocaine (0.15 and 0.25 g L-1), magnesium chloride (15 and 30 g L-1), and eugenol (0.25 and 0.5 mL L-1). The enzymatic activity (superoxide dismutase, catalase, glutathione peroxidase) and oxidative damage (TBARS, lipofuscins) were measured at 30, 60, and 120 min after immersion in each relaxant, and at 65 h representing the recovery period (filtered seawater with no relaxant). Propylene phenoxetol (2.5 mL L-1) and benzocaine (0.25 g L-1) induced > 80% relaxation within the first 45 min. Variations in the activity of superoxide dismutase activity were not significant between treatments in mantle and gills, but increased in muscle at 65 h in oysters exposed to 1.5 mL L-1 propylene phenoxetol and 15 and 30 g L-1 magnesium chloride. Control oysters significantly increased catalase activity in adductor muscle and gills (30-60 min), but the activity of glutathione peroxidase did not significant vary in muscle and mantle, and only decreased in gills at 65 h exposure to 2.5 mL L-1 propylene phenoxetol. Higher TBARS concentrations, as indicative of oxidative damage, only occurred at 30 min in muscle and gills in oysters exposed to 30 g L-1 magnesium chloride and 0.25 g L-1 benzocaine. Relaxing with benzocaine caused a significant accumulation of lipofuscins in gills at 120 min, again as possible indicator of oxidative stress; lowest lipofuscins values occurred with 1.5 mL L-1 propylene phenoxetol. These results confirm that propylene phenoxetol causes minimal interaction with antioxidant enzymes and provoke little oxidative damage to soft tissues in P. sterna.