Features of the free radical status of the follicular fluid of mares in the process of folliculogenesis

Background. The maturation of germ cells is a complex and multilevel process. To increase the effectiveness of assisted reproductive technologies in horses, a detailed study of the mechanisms of regulation of folliculogenesis is necessary.

Purpose. A lifetime study of the state of free radical status and the level of transcription factors regulating the antioxidant defense system in the follicular fluid (FF) of mares of the late transition period and the season of sexual cyclicity.

Materials and methods. The study was performed on mares, crossbreeds of heavy-duty, riding and Vyatka breeds, 6-12 years old in the spring transition period and the period of normal sexual cyclicity. 4 follicle groups were formed: large (≥31mm) follicles in the spring transition period, without signs of luteinization (group 1) and with signs of luteinization (group 2); large estrous follicles (>35 mm) in the ovulatory period without hormonal treatment (group 3) and with hormonal treatment (group 4). Photometric methods were used to determine the concentration of lipid peroxidation products – TBK-reactive products and protein oxidation products – carbonyl derivatives of proteins; the activity of antioxidant enzymes – superoxide dismutase and glutathione peroxidase and the level of endogenous antioxidant glutathione. The relative amounts of Nrf2, HIF-1a, VEGF and NFkB proteins were analyzed using the wester blot method.

Results. In the follicles of group 3, the concentration of TBK-reactive products and carbonyl derivatives of proteins increased significantly and exceeded the values of groups 1, 2 and 4. The content of non-protein SH groups reached a maximum level in the SH-group 4, exceeding the indicators of groups 1 and 3. The activity of superoxide dismutase and glutathione peroxidase significantly increased in group 4 relative to group 1. The level of Nrf2 increased in the SH-group 4, HIF1a – 2 and 3 groups, NFkB and VEGFA – in group 2.

Conclusion. The growth of the follicle and its preparation for ovulation in cycling mares in the summer is accompanied by the development of oxidative stress, which leads to the activation of the redox-sensitive factor Nrf2, followed by an increase in the activity of antioxidant enzymes superoxide dismutase and glutathione peroxidase and the level of endogenous antioxidant glutathione. For large follicles with signs of luteinization in the spring transition period, an increase in the level of VEGF and NFkB is characteristic in the FF, which may reflect the development of local hypoxia and inflammation and cause the development of the follicle along the path of luteinization without ovulation.