Hyperbaric oxygenation applied before or after mild or hard stress: effects on the redox state in the muscle tissue

The mechanism is unclear for the reported protective effect of hyperbaric oxygen preconditioning against oxidative stress in tissues, and the distinct effects of hyperbaric oxygen applied after stress. The trained mice were divided into three groups: the control, hyperbaric oxygenation preconditioning, and hyperbaric oxygenation applied after mild (fasting) or hard (prolonged exercise) stress. After preconditioning, we observed a decrease in basal levels of nitric oxide, tetrahydrobiopterin, and catalase despite the drastic increase in inducible and endothelial nitric oxide synthases. Moreover, the basal levels of glutathione, related enzymes, and nitrosative stress only increased in the preconditioning group. The control and preconditioning groups showed a similar mild stress response of the endothelial and neuronal nitric oxide synthases. At the same time, the activity of all nitric oxide synthase, glutathione (GSH) in muscle, declined in the experimental groups but increased in control during hard stress. The results suggested that hyperbaric oxygen preconditioning provoked uncoupling of nitric oxide synthases and the elevated levels of GSH in muscle during this study, while hyperbaric oxygen applied after stress showed a lower level of GSH but higher recovery post-exercise levels in the majority of antioxidant enzymes. We discuss the possible mechanisms of the redox response and the role of the nitric oxide in this process.

Participation of COX-1 and COX-2 in the contractile effect of phenylephrine in prepubescent and old rats

Vascular reactivity can be influenced by the vascular region, animal age, and pathologies present. Prostaglandins (produced by COX-1 and COX-2) play an important role in the contractile response to phenylephrine in the abdominal aorta of young rats. Although these COXs are found in many tissues, their distribution and role in vascular reactivity are not clear. At a vascular level, they take part in the homeostasis functions involved in many physiological and pathologic processes (e.g., arterial pressure and inflammatory processes). The aim of this study was to analyze changes in the contractile response to phenylephrine of thoracic/abdominal aorta and the coronary artery during aging in rats. Three groups of rats were formed and sacrificed at three distinct ages: prepubescent, young and old adult. The results suggest that there is a higher participation of prostanoids in the contractile effect of phenylephrine in pre-pubescent rats, and a lower participation of the same in old rats. Contrarily, there seems to be a higher participation of prostanoids in the contractile response of the coronary artery of older than pre-pubescent rats. Considering that the changes in the expression of COX-2 were similar for the three age groups and the two tissues tested, and that expression of COX-1 is apparently greater in older rats, COX-1 and COX-2 may lose functionality in relation to their corresponding receptors during aging in rats.