Decreased luteinizing hormone-stimulated progesterone secretion by preovulatory follicles isolated from cyclic rats treated with the progesterone antagonist RU486

Low-Dose Sodium Salicylate Promotes Ovulation by Regulating Steroids via CYP17A1

To meet the current demand of assisted reproduction and animal breeding via superovulation and reduce the impact of hormone drugs, it is necessary to develop new superovulation drugs. This study examined the role of inflammation and steroids in ovulation. Sodium salicylate can regulate inflammation and steroids. However, the effect of sodium salicylate on ovulation has not been studied. In this study, mice were intraperitoneally injected with different concentrations of sodium salicylate for four consecutive days. The effects of sodium salicylate on oocyte quality and on the number of ovulations were examined, and these effects were compared with those of pregnant horse serum gonadotropin (PMSG)/follicle-stimulating hormone (FSH) treatment. We found that low-dose sodium salicylate increased the levels of ovulation hormones and inflammation by promoting the expression of CYP17A1. Sodium salicylate had the same effect as the commonly used superovulation drug PMSG/FSH and reduced the histone methylation level. Sodium salicylate can promote ovulation in mice and Awang sheep. It can greatly decrease the use of hormone drugs, reduce breeding costs and physical impacts, and can thus be used for livestock breeding.

Ovulation: Parallels With Inflammatory Processes

The midcycle surge of LH sets in motion interconnected networks of signaling cascades to bring about rupture of the follicle and release of the oocyte during ovulation. Many mediators of these LH-induced signaling cascades are associated with inflammation, leading to the postulate that ovulation is similar to an inflammatory response. First responders to the LH surge are granulosa and theca cells, which produce steroids, prostaglandins, chemokines, and cytokines, which are also mediators of inflammatory processes. These mediators, in turn, activate both nonimmune ovarian cells as well as resident immune cells within the ovary; additional immune cells are also attracted to the ovary. Collectively, these cells regulate proteolytic pathways to reorganize the follicular stroma, disrupt the granulosa cell basal lamina, and facilitate invasion of vascular endothelial cells. LH-induced mediators initiate cumulus expansion and cumulus oocyte complex detachment, whereas the follicular apex undergoes extensive extracellular matrix remodeling and a loss of the surface epithelium. The remainder of the follicle undergoes rapid angiogenesis and functional differentiation of granulosa and theca cells. Ultimately, these functional and structural changes culminate in follicular rupture and oocyte release. Throughout the ovulatory process, the importance of inflammatory responses is highlighted by the commonalities and similarities between many of these events associated with ovulation and inflammation. However, ovulation includes processes that are distinct from inflammation, such as regulation of steroid action, oocyte maturation, and the eventual release of the oocyte. This review focuses on the commonalities between inflammatory responses and the process of ovulation.

X-linked lymphocyte regulated gene 5c-like (Xlr5c-like) is a novel target of progesterone action in granulosa cells of periovulatory rat ovaries

Progesterone (P4), acting through its nuclear receptor (PGR), plays an essential role in ovulation by mediating the expression of genes involved in ovulation and/or luteal formation. To identify ovulatory specific PGR-regulated genes, a preliminary microarray analysis was performed using rat granulosa cells treated with hCG ± RU486 (PGR antagonist). The transcript most highly down-regulated by RU486 was an EST (expressed sequence tag) sequence (gb: BI289578.1) that matches with predicted sequence for Xlr5c-like mRNA. Since nothing is known about Xlr5c-like, we first characterized the expression pattern of Xlr5c-like mRNA in the rat ovary. The level of mRNA for Xlr5c-like is transiently up-regulated in granulosa cells of periovulatory follicles after hCG stimulation in PMSG-primed rat ovaries. The transient induction of Xlr5c-like mRNA was mimicked by hCG treatment in cultured granulosa cells from preovulatory ovaries. We further demonstrated that the LH-activated PKA, MEK, PI3K, and p38 signaling is involved in the increase in Xlr5c-like mRNA. The increase in Xlr5c-like mRNA was abolished by RU486. The inhibitory effect of RU486 was reversed by MPA (synthetic progestin), but not by dexamethasone (synthetic glucocorticoid). Furthermore, mutation of SP1/SP3 and PGR response element sites in the promoter region of Xlr5c-like decreased Xlr5c-like reporter activity. RU486 also inhibited Xlr5c-like reporter activity. ChIP assay verified the binding of PGR and SP3 to the Xlr5c-like promoter in periovulatory granulosa cells. Functionally, siRNA-mediated Xlr5c-like knockdown in granulosa cell cultures resulted in reduced levels of mRNA for Snap25, Cxcr4, and Adamts1. Recombinant Xlr5c-like protein expressed using an adenoviral approach was localized predominantly to the nucleus and to a lesser extent to the cytoplasm of rat granulosa cells. In conclusion, this is the first report showing the spatiotemporally regulated expression of Xlr5c-like mRNA by hCG in rat periovulatory ovaries. P4/PGR mediates the LH-induced increase in Xlr5c-like mRNA. In turn, Xlr5c-like is involved in regulating the expression of specific ovulatory genes such as Snap25, Cxcr4, and Adamts1, possibly acting in the nucleus of periovulatory granulosa cells.

The role of steroids in follicular growth

The steroidogenic pathway within the ovary gives rise to progestins, androgens and oestrogens, all of which act via specific nuclear receptors to regulate reproductive function and maintain fertility. The role of progestins in follicular growth and development is limited, its action confined largely to ovulation, although direct effects on granulosa cell function have been reported. Consistent with these findings, progesterone receptor knockout mice are infertile because they cannot ovulate. Androgens have been shown to promote early follicular growth, but also to impede follicular development by stimulating atresia and apoptosis. The inability of androgens to transduce a signal in mice lacking androgen receptors culminates in reduced fertility. Oestrogens are known to exert effects on granulosa cell growth and differentiation in association with gonadotrophins. Studies with oestrogen receptor knockouts and oestrogen depleted mice have shown us that oestrogen is essential for folliculogenesis beyond the antral stage and is necessary to maintain the female phenotype of ovarian somatic cells. In summary, the action of steroids within the ovary is based on the developmental status of the follicle. In the absence of any single sex steroid, ovarian function and subsequently fertility, are compromised.

Gonadotropin surge induces two separate increases in messenger RNA for progesterone receptor in bovine preovulatory follicles

In mice deficient in progesterone receptor (PR), follicles of ovulatory size develop but fail to ovulate, providing evidence for an essential role for progesterone and PR in ovulation in mice. However, little is known about the expression and regulation of PR mRNA in preovulatory follicles of ruminant species. One objective of this study was to determine whether and when PR mRNA is expressed in bovine follicular cells during the periovulatory period. Luteolysis and the LH/FSH surge were induced with prostaglandin F(2alpha) and a GnRH analogue, respectively, and the preovulatory follicle was obtained at 0, 3.5, 6, 12, 18, or 24 h after GnRH treatment. RNase protection assays revealed a transient increase in levels of PR mRNA, which peaked at 6 h after GnRH and declined to the time 0 value by 12 h and a second increase at 24 h. The second objective was to investigate the mechanisms that regulate PR mRNA expression through in vitro studies on follicular cells of preovulatory follicles obtained before the LH/FSH surge. Theca and granulosa cells were isolated and cultured with or without a luteinizing dose of LH or FSH, progesterone, LH + progesterone, or LH + antiprogestin (RU486). Levels of PR mRNA increased in a time-dependent manner in granulosa cells cultured with LH or FSH and in theca cells cultured with LH, peaking at 10 h of culture. In contrast, progesterone (200 ng/ml) did not upregulate mRNA for its own receptor, and neither progesterone nor RU486 affected LH-stimulated PR mRNA accumulation. Furthermore, RU486 completely blocked LH-stimulated expression of oxytocin mRNA, indicating that PR induced by LH in vitro is functional. These results show that the gonadotropin surge induces a rapid and transient increase in expression of PR mRNA in both theca and granulosa cells of bovine periovulatory follicles followed by a second rise close to the time of ovulation and that the first increase in PR mRNA can be mimicked in vitro by gonadotropins but not by progesterone. These results suggest multiple and time-dependent roles for progesterone and PR in the regulation of periovulatory events in cattle.

Involvement of progesterone in gonadotrophin-induced pituitary adenylate cyclase-activating polypeptide gene expression in pre-ovulatory follicles of rat ovary

The present study was designed to determine whether progesterone might have a role in gonadotrophin-induced pituitary adenylate cyclase-activating polypeptide (Pacap) gene expression in rat ovary. Northern blot analysis revealed that treatment of pregnant mare's serum gonadotrophin (PMSG)-primed immature rats with the progestin antagonist RU486 or an inhibitor of 3beta-hydroxysteroid dehydrogenase epostane, 1 h before HCG, resulted in a dose-dependent inhibition of the HCG-induced Pacap gene expression. In-situ hybridization demonstrated that the number of pre-ovulatory follicles expressing Pacap mRNA in their granulosa cells was greatly reduced in ovaries treated with RU486. Moreover, the suppressive effect of RU486 or epostane on the LH-induced Pacap gene expression in cultured pre-ovulatory follicles was reversed by co-treatment with the synthetic progestin R5020. We further cloned the 5'-flanking region of the rat Pacap gene and identified the presence of a consensus progesterone receptor element. When luciferase fusion genes containing Pacap gene promoter were transiently transfected into granulosa cells of pre-ovulatory follicles, luciferase activity was markedly stimulated by LH. Treatment with RU486 or epostane resulted in partial suppression of LH-stimulated PACAP promoter activity. Taken together, these results indicate that progesterone, acting through progesterone receptors, plays a role in gonadotrophin induction of Pacap gene expression in granulosa cells of pre-ovulatory follicles, and thereby may be involved in the process of ovulation.

Flow cytometry of porcine ovarian cells: antiprogestins play an important role in progesterone receptor upregulation

To investigate the mechanism of antiprogestins in the regulation of ovarian function, a dual-chamber culture system was prepared with the amnion membrane of human placenta. Isolated porcine granulosa and thecal cells were grown on both sides of the amnion and co-cultured with or without RU486 and ZK98, 734. After 48 h incubation, the progesterone receptor (PR) and estrogen receptor (ER) of both cells were detected by flow cytometry. Progesterone and estradiol concentrations in the media were measured by radioimmunoassay. The results showed that antiprogestins increased PR contents in both cells; no significant change was found for ER. At the same time the progesterone and estradiol production by granulosa cells was inhibited; the progesterone production by thecal cells was reduced also. These data suggest that progesterone regulates progesterone synthesis. This autocrine/paracrine action may be the approach through which progesterone controls PR upregulation. It could be one mechanism for the inhibition of follicle development and steroidogenic function by antiprogestins.

The antiovulatory effect of the antiprogestin onapristone could be related to down-regulation of intraovarian progesterone (receptors)

The present study was undertaken to investigate intraovarian mechanism(s) for the antiovulatory effect of Onapristone (ON), because antiprogestins possessing the same antiprogestational activity and inhibiting the preovulatory LH surge to the same extent differ in their antiovulatory potency. Ovulation was induced by treating immature female rats with pregnant mare serum gonadotropin (PMSG) for folliculogenesis and hCG for the induction of ovulation. The animals were treated twice with ON (200 mg/kg 42 h and 48 h after PMSG) and killed at different times. The ovulation rate was assessed by counting the number of ova in the fallopian tubes and uteri. Blood and ovaries were collected for radioimmunoassay (RIA) of steroid hormones and histological analysis for 3beta-hydroxysteroid dehydrogenase (3beta-HSDH), 17beta-hydroxysteroid dehydrogenase (17beta-HSDH), progesterone (PR), estrogen (ER) and androgen (AR) receptors. Treatment with ON totally blocked ovulation and the progesterone (P4) surge was significantly diminished in comparison to the control (6-8 h post-hCG), whereas androgen levels remained unaffected. The decreased P4 concentrations correlated well with a reduced staining intensity of 3beta-HSDH in granulosa cells of tertiary follicles. Moreover, we observed a down-regulation of PR in granulosa cells of tertiary follicles. Additionally, in secondary and tertiary follicles the expression of AR between 0 and 6 h after hCG was reduced. These results suggest that the antiovulatory effect of the antiprogestin ON is related to down-regulation of intraovarian progesterone, caused by attenuated 3beta-HSDH activity and PR expression. One can thus assume that intraovarian P4 is an important factor for the induction of ovulation. An effect of ON on the staining intensity of 17beta-HSDH in theca and granulosa cells could not be observed at any time. In conclusion, the inhibition of ovulation induced by the antiprogestin, ON, could be related to decreased intraovarian progesterone production through reduced 3beta-HSDH activity and the down-regulation of PR.

The antiovulatory activity of progesterone antagonists is not correlated to their antiprogestational potency in the rat

Progesterone antagonists often differ in regard to their potency to block ovulation in rats although they may possess similar 'antiprogestational' (abortive) activity. Therefore, the questions arose as to: (a) whether antiovulatory and antiprogestational effects (on endometrial and mammary gland parameters) of antiprogestins correlate at all; and (b) which mechanism(s) may be responsible for their ability to abolish ovulation. To answer these questions we set out to compare the influences of two progesterone antagonists, Onapristone (ON) a very potent and ZK 136798 only a weak inhibitor of ovulation, to assess changes on the one hand on typical progestational actions and on the other hand on factors known to regulate ovulation. For this purpose immature PMSG/hCG primed and adult female rats and infantile female rabbits were treated either with ON, ZK 136798 or vehicle in different treatment schedules. In these investigations ON and ZK 136798 showed similar antiprogestational activities on the progesterone-induced development of mammary glands (rats) and the secretory transformation of endometrium (rabbits). ON blocked an induced or a spontaneous ovulation, whereas ZK 136798 only revealed a very weak antiovulatory effect. Both ON and ZK 136798 stimulated basal levels of LH, estradiol, and testosterone, whereas the preovulatory LH surge was decreased to the same extent. Interestingly, in contrast to ZK 136798, ON reduced the preovulatory increase in progesterone secretion. These results clearly indicate: (a) that antiovulatory potency and antiprogestational activity may not be correlated in the rat; and (b) that decreased preovulatory levels of progesterone following treatment with ON may play an important role in intraovarian mechanism(s) contributing to a blocking of ovulation.

Luteolytic action of RU486: modulation of luteal 3 beta-hydroxysteroid dehydrogenase and 20 alpha-hydroxysteroid dehydrogenase activities in late pregnant rats

The effect of the synthetic antiprogestin RU486 on luteal function in late pregnant rats was studied by evaluating the activities of the enzymes 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD). RU486 (2 mg/kg) administered to rats on day 18 of pregnancy at 10.00 h induced preterm delivery 26.4 +/- 0.35 h (n = 8) after treatment. Luteal 3 beta-HSD activity increased 24 and 34 h after RU486 injection, but a significant and progressive decrease started at 48 h with the maximal reduction 72 h after RU486 treatment, when compared with controls. Serum progesterone concentration decreased at the time of 3 beta-HSD activity reduction. Interestingly, 20 alpha-HSD activity started to increase 58 h after RU486 injection. The administration of the cyclooxygenase inhibitor, diclofenac (1.3 mg/kg), on days 17-19 of pregnancy to RU486-treated rats, delayed abortion and the duration of delivery, and prevented the decrease in 3 beta-HSD and the increase in 20 alpha-HSD activities observed 58 h after antiprogesterone treatment. RU486 administered intrabursally (1 microgram per ovary) on day 20 (14.00-15.00 h) increased 3 beta-HSD and decreased 20 alpha-HSD luteal activities at 18.00 h on day 21 of pregnancy, without modifying serum progesterone concentration, when compared with normal pregnant rats. In conclusion, the luteolytic process after preterm delivery induced by RU486 administration in late pregnant rats is characterized by a decrease in luteal 3 beta-HSD activity and circulating progesterone, which may trigger the increase in luteal 20 alpha-HSD activity. Prostaglandins seems to be involved in the increase of 20 alpha-HSD activity and therefore, in the demise of corpora lutea.

Disturbance of follicular development and endocrine reactions induced by the antiovulatory effective progesterone antagonist Onapristone

The present study was undertaken to investigate whether inhibition of ovulation, which is known to occur after treatment with progesterone antagonists, is due to the effect of high levels of prolactin. Therefore, rats with 4-day cycles were treated with the antiprogestin, Onapristone (ON), once daily starting on the evening of estrus. It was detected that the profile of peripheral prolactin levels during the treatment with ON was not remarkably different from that found in the controls. Furthermore, bromocriptine, a prolactin antagonist, was not able to reverse the antiovulatory potency of ON. It is concluded that the antiovulatory effect of ON might not be related to changes in the level of prolactin. Nevertheless, prolactin levels remained high after the preovulatory surge. Thus, we cannot exclude the possibility that PRL plays a role in the induction of anovulatory cycles observed during long term treatment. In animals treated for the length of one cycle we found that the preovulatory LH surge decreased but it remains questionable whether this contributes to the inhibition of ovulation by ON. Interestingly, basal LH, androgen and estrogen levels were elevated. Accordingly, we favour the idea that LH stimulates the theca interstitial cells to produce excessive amounts of androgens which may be aromatized into estrogens. These high levels of androgens and estrogens may contribute to the antiovulatory mechanism of ON by disturbing physiological follicular development. In fact, a morphometrical analysis revealed an increase in the volume density of late tertiary follicles. The increased progesterone levels may also be related to high basal LH levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of mifepristone (RU 486) on ovulation in the isolated perfused rat ovary

The antigestagen mifepristone (RU 486) acts by blocking the progesterone receptor. Mifepristone has been used clinically for medical termination of pregnancy. It has recently also been shown that it can be used as an effective contraceptive agent in many species including the human. This contraceptive effect is acquired through prolonged exposure to mifepristone during the follicular phase and has been linked to disrupted folliculogenesis and inhibition of the LH surge. In the present study it is tested if mifepristone inhibits ovulation by a direct action on the ovary at the time of the LH surge. Preovulatory rat ovaries from immature Sprague-Dawley rats primed with 20IU of equine CG were perfused in vitro for 20 h in the presence of LH and 3-isobutyl-1-methylxanthine (IBMX) to induce ovulations. Mifepristone was added to study the effect on ovulation rate and ovarian steroidogenesis. Unstimulated control ovaries did not ovulate whereas addition of ovine LH (0.1 microgram/ml) and IBMX (0.2mM) resulted in 17.6 +/- 2.7 ovulations per treated ovary. Presence of mifepristone at 1 microM did not significantly inhibit LH+IBMX-induced ovulation (13.0 +/- 1.2) whereas mifepristone at 50 microM significantly (p < 0.01) inhibited ovulation (2.8 +/- 1.4). When the latter dosage of mifepristone (50 microM) was added 4h after LH+IBMX, no inhibitory effect was seen (17.2 +/- 3.0). Progesterone and estradiol release was significantly increased by LH+IBMX over the control group. Presence of mifepristone at any tested dose or time of addition did not significantly change the LH+IBMX-stimulated steroid release. It is concluded that mifepristone inhibits ovulation in the rat at the ovarian level when present just before LH stimulation but not when administered 4h into the ovulatory process.