Effect of regular exercise on reproductive function of aged female mice

Abstract

This study was aimed to examine whether regular exercise can improve the expression of ovarian anigogenic factors, oocyte quality and fertility potential in aged female mice. Firstly, 40 C57BL female mice of 30-32 weeks were divided into the two groups. One group (n=20) were regularly exercised (physical activity) by illuminating incandescent lights (60 Watts, 220V), placed on the top of the cage, for 30 minutes daily. The other group (n=20) were served as control without exercise. After 4 weeks, the female mice were mated with the same strained individual male mice of 12 weeks during 2 weeks maintaining the exercise protocol. Then pregnancy was observed for subsequent 2 weeks (1st observation). Mice that were not pregnant were re-mated during further 2 weeks and re-examined the pregnancy outcome for the following 2 weeks (2nd observation). Secondly, female mice of two age groups (6-8 weeks and 30-32 weeks) were treated with exercise protocol for 6 weeks, and then superovulated with pregnant mare serum gonadotrophi, followed by human chorionic gonadotrophin injection 48 hours later. Then they were mated with individual males. After 18 hours, zygotes were flushed and cultured to blastocyst. Just after zygote retrieval, both ovaries were collected and ovarian vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) expression was examined using western blot and immunohistochemistry, and ovarian apoptosis was assessed by TUNEL method. The total number of pregnant mice was 15 (75%) in the exercise group, which was significantly higher than 5 (25%) in the control group (P<.05). The mean number of offspring was also significantly higher in the exercise group (9.2) than the control group (6.3) (P <.05). The mean number of one-cell embryos retrieved and blastocyst formation rate were 12.6 and 43.8% in the exercise group and 10.8 and 8.1% in the control group with a significant difference (P<.05). Ovarian VEGF and eNOS expression was increased, but ovarian apoptosis was decreased in the exercise group. This study demonstrates that regular exercise induced by illumination with incandescent lights in aged mice improves their reproductive outcomes by improving ovarian function and oocytes quality. The beneficial effect of an optimal exercise on fertility may be associated with the activation of ovarian angiogenesis by increasing ovarian eNOS and VEGF expression.