Heat stress diminishes gonadotropin receptor expression and enhances susceptibility to apoptosis of rat granulosa cells

Abstract

Heat stress inhibits ovarian follicular development in mammalian species. We hypothesized that heat stress inhibits the function of follicular granulosa cells and suppresses follicular development. To test this, immature female rats were injected with pregnant mare serum gonadotropin (PMSG) at 48 h after the start of temperature treatment (control: 25 8C, 50% RH; heat stress: 35 8C, 70% Relative Humidity). The ovaries and granulosa cells of follicles at different developmental stages were analyzed for gonadotropin receptor levels and aromatase activity; estradiol levels were measured in follicular fluid. Before injection, heat stress diminished only the amount of FSH receptor on granulosa cells of antral follicles. During PMSG-stimulated follicular development, heat stress strongly inhibited gonadotropin receptor levels and aromatase activity in granulosa cells, and estradiol levels in the follicular fluid of early antral, antral and preovulatory follicles. To examine apoptosis and mRNA levels of bcl-2 and bax in granulosa cells, follicles harvested 48 h after PMSG injection were cultured in serum-free conditions. Heat-stressed granulosa cells showed a time-dependent increase in apoptosis. The bcl-2 mRNA levels were similar in control and heat-stressed granulosa cells; bax mRNA levels were increased in heat-stressed granulosa cells. According to these results, heat stress inhibits expression of gonadotropin receptors in granulosa cells and attenuates estrogenic activity of growing follicles, granulosa cells of heat-stressed follicles are susceptible to apoptosis, and the bcl2/bax system is not associated with heat-stress-induced apoptosis of granulosa cells. Our study suggests that decreased numbers and function of granulosa cells may cause ovarian dysfunction in domestic animals in summer.

Effects of Seasonal Changes on In Vitro Developmental Competence of Porcine Oocytes

“…Additionally, heat stress was found to change the numbers of follicles and their diameters [6] and also to modify the fatty acid [6] and protein [18] composition of the porcine oocyte plasma membrane. Furthermore, heat stress induces reactive oxygen species and results in apoptosis of granulosa cells in mice and rats [19,20]. As reported in previous bovine studies [6][7][8], the present results clearly showed a negative relationship between developmental competence of porcine oocytes and atmospheric temperatures.…”

The effect of heat stress on gene expression, synthesis of steroids, and apoptosis in bovine granulosa cells

“…The higher temperature induced an oversecretion of ovarian hormones in porcine ovarian granulosa cells (Sirotkin 2010). But some studies show that heat stress diminishes gonadotropin receptor expression and attenuates estrogenic activity in rat granulosa cells (Shimizu et al 2005). Our study is the first that demonstrated the effect of heat stress on gene expression and steroid hormone synthesis in bovine ovarian granulosa cells.…”

“…The lack of estradiol leads to granulosa cell apoptosis (Shimizu et al 2005). Thus, we hypothesized that apoptosisrelated genes might be expressed in heat treatment GCs.…”

Natural influence of season on follicular, luteal, and endocrinological turnover in Indian crossbred cows

“…The ovulatory follicle attained a significantly larger diameter (12.8 mm) during the hot season to express estrus signs than the cold season (11.2 mm), which might be suggestive of alterations in steroidogenesis within the follicular microenvironment [21,22]. As stated by AlKatanani et al [23], the imbalances in energy metabolism, which occurred to maintain the body temperature at normal levels during the hot season, would have suppressed the aromatase activity in granulosa cells and retarded the functionality of DFs.…”