Ovariectomy-induced chronic abdominal hypernociception in rats: Relation with brain oxidative stress

Context: Ovarian hormone deficiency observed in menopausal women increases the production of reactive oxygen species, which could be implicated in central sensitization subjacent in chronic functional pain syndromes. Aims: To examine the hyperalgesic state induced by ovariectomy in adult rats and its relation to some oxidative stress outcomes. Methods: The female Wistar rats were divided into normal, sham ovariectomized (OVX) and OVX groups, which were tested for mechanical and thermal hypernociception during 6 weeks and a single acetic acid-induced test 6 weeks after surgery. Redox biomarkers determinations of superoxide dismutase (SOD) enzyme activity, glutathione (GSH) and nitrates/nitrites as an indicator of nitric oxide (NO) concentrations were determined in the brain and cerebellum of 6 animals of each group. Results: Exclusivity OVX rats developed a robust state of mechanical hypernociception and allodynia in the abdomen, hindlimbs and proximal tail. Besides, thermal pain thresholds (hot plate) decreased. That was established 3-4 weeks after OVX and lasted for the 6 weeks of the experiment. Increases in visceral sensitivity were also observed in OVX rats. SOD enzyme activity decreased in OVX rats, which showed major deficit for this enzymatic defense under visceral inflammatory injury. However GSH concentrations were increased in brain of OVX animals that allow the balance during acute inflammation. NO concentrations were raised only in OVX rats exposure to chemical inflammatory injury. Conclusions: OVX in rats provide a useful model, which mimics the functional pain in females that could be related with brain oxidative stress.