Heat stress during summer reduced the ovarian aromatase expression of sows in Korea

초록

It has been addressed that heat stress due to high atmospheric temperature during summer in Korea induces impaired release of reproductive hormones, followed by occurring abnormal ovarian cyclicity, lower pregnancy ratio, and reduced litter size. Therefore, the present study attempted to compare seasonal change (spring versus summer) of the ovarian aromatase expression, an enzyme for converting testosterone into estrogen. While serum estrogen level in summer group was significantly lower than that of spring group, testosterone was not different between groups. Consistent with estrogen level, the ovarian aromatase expression in summer at follicular phase was significantly lower than the counterpart of spring. The ovarian aromatase expression was positively related with serum estrogen level significantly (r=0.689; P =0.008) and strongly negative correlation was identified (r=−0.533; P=0.078) with atmospheric temperature. The ovarian aromatase expression was not detected in immature ovarian follicles but specifically localized in the granulosa cell layers in both seasons. However, the aromatase intensity in the granulosa cell layers was stronger in spring than summer. Because testosterone level was not different between groups, it could be concluded that the lower level of estrogen during summer might be derived by not lack of substrate but lower expression of ovarian aromatase by heat stress.

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