Age-related changes in the bovine corpus luteum function and progesterone secretion.

Decreased fertility associated with maternal ageing is a well-known critical problem, and progesterone (P4) concentration decreases during the menopause transition in women. The corpus luteum (CL) secretes P4, thereby supporting the implantation and maintenance of pregnancy. It is proposed that a bovine model is suitable for studying age-associated decline of fertility in women because the physiology of cows is similar to that of women and cows have a greater longevity compared with other animal models. Thus, we investigated the age-dependent qualitative changes and inflammatory responses in the bovine CL. In vivo experiment: Cows were divided into three groups, namely, young (mean age: 34.8 months), middle (80.1 months) and aged (188.9 months). Blood samples were collected on days 7 and 12 during the estrous cycle. In vitro experiments: Cows were divided into young (mean age: 27.6 months) and aged (183.1 months). The CL tissues of these groups were collected from a local slaughterhouse and used for tissue culture experiments. An in vivo experiment, plasma P4 concentration in aged cows was significantly lower than that in young cows, whereas no difference was found regarding the area of CL. An in vitro examination in the bovine CL tissues showed that the luteal P4 concentration, P4 secretion, and mRNA expression of StAR and 3β-HSD were lower in aged cows compared with young cows, especially in the early luteal phase. However, no differences were detected in the mRNA expression of inflammation- and senescence-related factors and inflammatory responses to lipopolysaccharides between the CL tissues from young and aged cows, indicating that an age-dependent increase in inflammation is not involved in the luteal function. P4 production and secretion from the bovine CL diminish in old cows, especially during the early luteal phase, suggesting that senescence may affect the luteal function in cows.