Antioxidant enzyme dynamics suggest the absence of oxidative stress in the canine endometrium across the estrous cycle

Oxidative stress plays a vital role in female fertility, yet the mechanisms regulating oxidative balance in the canine endometrium remain poorly understood. This study investigates the dynamics of the antioxidant enzyme system in the canine endometrium, focusing on superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GSR), and glutathione-S-transferase (GST), along with thiobarbituric acid reactive substances (TBARS) and total cellular thiols. Enzyme activities were revealed in five different phases of oestrus cycle in 25 dogs, using a spectrophotometric method: anestrus, proestrus, estrus, early diestrus and diestrus (n = 5 per group). Notably, a distinctive pattern in SOD and CAT activity was observed, with the former being characterised by a decrease from anestrus to estrus, and the later showed an opposite increase from anestrus to diestrus. In contrast, the activities of the glutathione-dependent enzymes GPX, GSR, and GST remained remarkably stable, although showing some fluctuations in different stages. TBARS analysis indicated an evident increase in oxidative stress-related lipid peroxidation in the canine endometrium only between anestrus and proestrus. Conversely, the thiol cell content remained consistent within the cycle stages. Our examination of enzyme ratios underscores a delicate balance in the normal canine uterus, effectively controlling oxidative stress without causing damage to lipids or proteins due to excessive reactive oxygen species. These findings contribute to our understanding of the unique physiological dynamics of the canine endometrium, offering valuable insights into the intricate regulation of oxidative stress in this context and its potential implications for female fertility.