Glutathione protection against dive-associated ischemia/reperfusion in ringed seal tissues

Ischemia/reperfusion is a potentially hazardous condition that increases reactive oxygen species (ROS) production and oxidative damage. Seals of the phocid family experience repetitive episodes of ischemia/reperfusion during and after a dive as a consequence of preferential distribution of blood flow to the central nervous system and reduction or elimination of perfusion in most vascular beds. Previous studies showed that ROS production is higher in ringed seal than in domestic pig tissues as a direct consequence of the ischemia/reperfusion associated with the diving response; however, oxidative damage is not related to this high ROS production. Apparently, antioxidant enzyme activities participate in the antioxidant protection in ringed seal tissues. In the present study we addressed the potential antioxidant protection of the glutathione system against dive-induced ischemia/reperfusion in ringed seal tissues. Total glutathione (GSH-Eq = GSH + 2GSSG), glutathione (GSH) and glutathione disulfide (GSSG), the ratio GSSG:GSH-Eq, the activities of the enzymes glutathione disulfide reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH), as well as lipid peroxidation (TBARS) and carbonyl proteins, were measured in ringed seal and domestic pig heart, kidney, liver, lung and muscle samples. In heart, kidney, lung and muscle GSH-Eq and GSH content was higher in seal than in pig (p < 0.05). GSSG content was higher in seal than in pig heart kidney, liver and muscle (p < 0.05). GR and G6PDH activities were higher in all seal than in pig tissues (p < 0.05). GSSG:GSH-Eq ratio was higher in pig than in seal heart, and lung (p < 0.05). TBARS content was higher in pig than in seal lung (p < 0.05). Higher content of carbonyl proteins was present in pig than in seal heart, kidney, liver and muscle (p < 0.05). These results suggest that the glutathione levels and the activity of enzymes involved in its recycling are efficient mechanisms that ameliorate protein and lipid oxidative damage and protect ringed seal tissues against dive-induced ischemia/reperfusion.