Effects of Heat Stress on Follicular Development in PMSG-treated Immature Rats

Shimizu, Takashi; Ohshima, Izumi; Kanai, Yoshikatsu

doi:10.2508/chikusan.71.32

Cited by 5 publications

(5 citation statements)

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“…Our study indicates that heat stress suppresses FSH-R expression in granulosa cells of follicles at the early antral, antral and preovulatory stages after PMSG treatment. This finding suggests that the increase in atresia caused by heat stress (Shimizu et al 2000) may be induced by the inhibition of FSH-R expression in granulosa cells.…”

Section: Discussionmentioning

confidence: 72%

“…In domestic animals, heat stress has been found to reduce the size of the dominant follicle by day 8 (Badinga et al 1993) and between days 11 and 21 of the estrus cycle (Wilson et al 1998a,b). In rodents, heat stress promoted follicular atresia and resulted in a decreased number of oocytes ovulated in immature female rats primed with pregnant mare serum gonadotropin (PMSG) (Shimizu et al 2000).…”

Section: Introductionmentioning

confidence: 99%

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

Shimizu¹,

Ohshima²,

Ozawa³

et al. 2005

Reproduction

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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.

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Section: Discussionmentioning

confidence: 72%

Section: Introductionmentioning

confidence: 99%

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

Shimizu¹,

Ohshima²,

Ozawa³

et al. 2005

Reproduction

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“…Plasma FSH concentrations were not altered by heat stress in the present study. However, a recent study in immature rats indicated that heat stress suppressed equine chorionic gonadotrophin (eCG)-induced follicular growth and caused a significant reduction of FSH receptor content in the granulosa cells (Shimizu et al 2000). These combined findings suggests that heat-stressed follicles lack sufficient FSH stimulation to enhance the aromatase activity owing to decreased FSH receptor expression, rather than to diminished FSH levels, and that this leads to the observed decrease in oestradiol concentrations.…”

Section: Discussionmentioning

confidence: 74%

Alterations in follicular dynamics and steroidogenic abilities induced by heat stress during follicular recruitment in goats

Ozawa¹,

Tabayashi²,

Latief³

et al. 2005

Reproduction

103

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We investigated the changes in follicular dynamics and steroidogenic activity during heat stress in goats. Adult female goats were exposed to heat stress at 36 8C and 70% relative humidity for 48 h and then injected with prostaglandin (PG) F 2a (the time of PGF 2a injection was designated as 0 h). In experiment 1, every follicle greater than 2 mm in diameter was monitored by ultrasonography to investigate the follicular dynamics, and plasma concentrations of FSH, LH, progesterone, and oestradiol were measured from 248 h to 120 h. In experiment 2, the follicles were recovered from the goats at 48 h, and the concentration of oestradiol, the aromatase activity, and the LH receptor level in the follicles were determined. In control (non-heatstressed) goats, ovulatory follicles were mainly recruited from 224 h to 0 h, whereas no follicles recruited during that period were ovulated in the heat-stressed goats. The timing of the recruitment of ovulatory follicles was delayed by heat stress by approximately 24 h. The plasma concentration of oestradiol in the heat-stressed goats was significantly lower from 36 to 54 h compared with the controls, although the concentrations of FSH and progesterone did not differ between the treatments. In addition, the concentration of oestradiol, the aromatase activity, and the LH receptor level in the follicles from heat-stressed goats were significantly lower compared with the controls. These results indicate that heat stress during follicular recruitment suppresses subsequent growth to ovulation, accompanied by decreased LH receptor level and oestradiol synthesis activity in the follicles.

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“…For instance, animal studies show that heat stress during early pregnancy can reduce blood flow to the fetus with negative consequences for offspring birth weight [74], whereas cold exposure appears to increase glucose availability to the fetus [75]. In cattle and rodents, it has also been demonstrated that heat stress is capable of inhibiting follicular development by affecting estrogenic activity and the viability of granulosa cells [76][77][78]. Heat could also act indirectly as a non-specific stressor [73], with potential consequences for early developmental processes.…”

Section: Ambient Temperaturementioning

confidence: 99%

Season of Birth Effects on Reproduction in Women

Huber¹,

Fieder²

2007

CWHR

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Environmental conditions experienced during foetal and neonatal life influence early development with potential long-term consequences for later life events. In many parts of the world, the external environment varies with the season. This includes factors such as photoperiod, climatic factors, nutrition or prevalence of infectious agents. Birth season is one surrogate for the environmental conditions experienced at conception, during pregnancy, around birth and during early postnatal life. The seasonal variation of environmental factors may thus influence early pre-and postnatal developmental processes differently in individuals born at different times of the year, causing respective downstream effects on later life events. Accordingly there is accumulating evidence that effects of birth season may impact a variety of physical, physiological and psychological parameters in humans. This review covers a survey of birth season effects on reproductive characteristics in women together with a discussion of possible causes, focussing on environmental factors that might play a central role during development, crucial periods of early development that might be influenced by these environmental factors, and potential underlying physiological mechanisms.

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Effects of Heat Stress on Follicular Development in PMSG-treated Immature Rats

Abstract: Effects of heat stress on follicular development was studied in three-week-old immature female rats kept under 25℃ and 50% relative humidity (RH). In experiment 1, animals were divided

Cited by 5 publications

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

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

Alterations in follicular dynamics and steroidogenic abilities induced by heat stress during follicular recruitment in goats

Season of Birth Effects on Reproduction in Women

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