Rat ovarian prostaglandin levels and ovulation as indicators of the strength of non-steroidal anti-inflammatory drugs

Does injection of prostaglandin F2α (PGF2α) cause ovulation in anestrous Western White Face ewes?

In a previous study in our laboratory, treatment of non-prolific Western White Face (WWF) ewes with PGF(2 alpha) and intravaginal sponges containing medroxyprogesterone acetate (MAP) on approximately Day 8 of a cycle (Day 0 = first ovulation of the interovulatory interval) resulted in ovulations during the subsequent 6 days when MAP sponges were in place. Two experiments were performed on WWF ewes during anestrus to allow us to independently examine if such ovulations were due to the direct effects of PGF(2 alpha) on the ovary or to the effects of a rapid decrease in serum concentrations of progesterone at PGF(2 alpha)-induced luteolysis. Experiment 1: ewes fitted with MAP sponges for 6 days (n = 12) were injected with PGF(2 alpha) (n = 6; 15 mg im), or saline (n = 6) on the day of sponge insertion. Experiment 2: ewes received progesterone-releasing subcutaneous implants (n = 6) or empty implants (n = 5) for 5 days. Six hours prior to implant removal, all ewes received a MAP sponge, which remained in place for 6 days. Ewes from both experiments underwent ovarian ultrasonography and blood sampling once daily for 6 days before and twice daily for 6 days after sponge insertion. Additional blood samples were collected every 4 h during sponge treatment. Experiment 1: 4-6 (67%) PGF(2 alpha)-treated ewes ovulated approximately 1.5 days after PGF(2 alpha) injection; these ovulations were not preceded by estrus or a preovulatory surge release of LH, and resulted in transient corpora hemorrhagica (CH). The growth phase was longer (P < 0.05) and the growth rate slower (P < 0.05) in ovulating versus non-ovulating follicles in PGF(2 alpha)-treated ewes. Experiment 2: in ewes given progesterone implants, serum progesterone concentrations reached a peak (1.7 2 ng/mL; P < 0.001) on the day of implant removal and decreased to basal concentrations (<0.17 ng/mL; P < 0.001) within 24 h of implant removal. No ovulations occurred in either the treated or the control ewes. We concluded that ovulations occurring after PGF(2 alpha) injection, in the presence of a MAP sponge, could be due to a direct effect of PGF(2 alpha) at the ovarian level, rather than a sudden decline in circulating progesterone concentrations.

Morphodynamics of the follicular-luteal complex during early ovarian development and reproductive life

Female reproductive activity depends upon cyclic morphofunctional changes of the ovarian tissue during the female's fertile period, but the primum movens of an active gonadal rearrangement can be found from early phases of embryo development. To offer a basic account of the main steps of ovarian dynamics, we review the morphofunctional behavior of the follicular-luteal complex in an integrated study using light microscopy and transmission and scanning electron microscopy as well as through the use of numerous drawings. Particular emphasis is given to some reproductive aspects including (1) germ-somatic cell relationships and onset of folliculogenesis during early gonadal development; (2) follicular development and oocyte-follicle cell associations through adult folliculogenesis, finally leading to ovulation; (3) morphodynamics of corpus luteum formation, development, and regression, and (4) degenerative processes involving germ and somatic cells. The results reported, many of which originated in our laboratory, arise from some experiments on laboratory mammals but mostly from a large selection of human specimens. The data obtained are integrated and correlated with classic reports as well as with current views. Crucial biochemical, histophysiological, and clinical aspects are also emphasized.

Aspirin dose dependently inhibits the interleukin-1 beta-stimulated increase in inducible nitric oxide synthase, nitric oxide, and prostaglandin E(2) production in rat ovarian dispersates cultured in vitro

OBJECTIVE

Determine if aspirin inhibits the IL-1 beta-stimulated expression of inducible nitric oxide synthase (iNOS), nitric oxide (NO), and prostaglandin E(2) (PGE(2)) in rat ovarian dispersates cultured in vitro.

DESIGN

Prospective, controlled in vitro study.

SETTING

Academic research laboratory.

ANIMALS

Ovaries collected from immature rats.

INTERVENTION(S)

Ovaries were collected from immature rats and enzymatically dispersed. Ovarian dispersates were placed into plates containing media alone or media supplemented with IL-1 beta (100 U/mL) and varying concentrations of aspirin (0, 1, 3, 5 and 10 mM). Ovarian dispersates were cultured in a humidified environment of 5% CO(2) in air at 37 degrees C for 24 or 48 hours.

MAIN OUTCOME MEASURE(S)

Twenty-four- and 48-hour iNOS, nitrite (a stable metabolite of NO), and PGE(2) levels were determined from ovarian dispersates cultured in vitro.

RESULT(S)

Administration of IL-1 beta increased nitrite and PGE(2) levels over that observed in the control group after culture of ovarian dispersates for 24 and 48 hours. Aspirin dose dependently reduced the IL-1 beta-stimulated increase in nitrite production from ovarian dispersates after culture for 24 and 48 hours. Aspirin completely (24 hours) or dose dependently (48 hours) prevented the IL-beta-stimulated increase in PGE(2.) Coadministration of IL-1 beta and aspirin (10 mM) attenuates IL-1 beta-stimulated iNOS expression after culture for 24 and 48 hours.

CONCLUSION(S)

Aspirin significantly inhibits the IL-1 beta-stimulated expression of iNOS, NO, and PGE(2) in ovarian dispersates cultured in vitro.

Prostaglandin-independent anovulatory mechanism of indomethacin action: inhibition of tumor necrosis factor alpha-induced sheep ovarian cell apoptosis

Indomethacin, a nonsteroidal anti-inflammatory agent, is a potent inhibitor of ovulation in vertebrates. The presumptive obligate anovulatory mode of indomethacin action is via suppression of ovarian prostaglandin production. We report that a very high systemic dose of indomethacin (800 mg i.m.) is required to block ovulation in gonadotropin-treated anestrous ewes. A lower dose of indomethacin (200 mg), which negated the preovulatory rise in follicular prostaglandin (PGF(2alpha)) biosynthesis, did not prevent ovulation. Endothelial secretion of tumor necrosis factor (TNF)-alpha within the apical follicular wall (prospective site of rupture) was not altered by indomethacin; notwithstanding, the apoptosis (DNA-fragmentation)-inducing effect of TNF-alpha (a determinant of ovulatory stigma formation) was attenuated by 800 (but not 200) mg indomethacin. A suprapharmacological concentration of indomethacin also was necessary to protect ovarian surface epithelial cells from a (prostaglandin-independent) cytotoxic effect of TNF-alpha in vitro. It is concluded that indomethacin inhibits ovulation by anti-apoptotic mechanisms that can be dissociated from the paradigm of prostanoid down-regulation.

Effects of nitric oxide on ovulation and ovarian steroidogenesis and prostaglandin production in the rabbit

Evidence supports the involvement of nitric oxide (NO) in ovarian physiology. The present study was undertaken to investigate the role of the NO/NO synthase (NOS) systems in ovulation, oocyte maturation, ovarian steroidogenesis, and PG production using in vitro perfused rabbit ovaries. The addition of the NOS inhibitors, aminoguanidine hemisulfate salt (AG) and N-omega-nitro-L-arginine methyl ester (L-NAME), to the perfusate inhibited the ovulation induced by hCG in a dose-dependent manner, whereas D-NAME had no significant effect. Neither AG nor L-NAME affected the hCG-induced meiotic maturation of the ovulated ova. The exogenous administration of the NO generator, sodium nitroprusside (NP), induced follicle rupture in the absence of gonadotropin, but did not induce oocyte maturation. Inhibition of endogenous NOS by AG and L-NAME resulted in a significant elevation in the production of estradiol (E2), but not of progesterone, stimulated by hCG. The concomitant administration of NP significantly reduced the AG-stimulated production of E2 by ovaries perfused in the presence of hCG, which suggests that NO down-regulates ovarian E2 synthesis. Ovarian production of PGE2 and PGF2alpha in response to hCG was significantly blocked by L-NAME, and exogenous administration of NP stimulated the production of PGs in the absence of gonadotropin. Significant correlations were observed between the ovulatory efficiencies and the production of PGs by rabbit ovaries perfused with or without L-NAME. In conclusion, the ovarian NO/NOS system is involved in follicle rupture during the ovulatory process. NO may induce follicle rupture in rabbit ovaries at least in part by the stimulation of PG production.

Differential effects of indomethacin on the sheep ovary: prostaglandin biosynthesis, intracellular calcium, apoptosis, and ovulation

Cells of the apical wall of the dominant follicle and contiguous ovarian surface epithelium become apoptotic with the approach of ovulation in the sheep. It was hypothesized that indomethacin, an established inhibitor of prostaglandin biosynthesis and ovulation, would protect apical ovarian cells from programmed death. The anovulatory potencies of two systemic doses of indomethacin (200 and 800 mg) were tested in gonadotropin-stimulated ewes. A complete blockade of ovulation occurred at the higher dose of indomethacin. Ovulation was not inhibited by 200 mg indomethacin. Both doses of drug suppressed follicular prostaglandin production below pregonadotropin levels. Immunofluorescence detection of digoxigenin end-labeled (fragmented) DNA was used as a marker of apoptosis among ovarian surface epithelial and granulosa cells recovered from the optical hemisphere of preovulatory ovine follicles. Cellular DNA fragmentation was averted in animals given 800 mg indomethacin, whereas apoptosis ensued after 200 mg. A sustained increase in cytosolic calcium is generally a prerequisite to apoptotic DNA fragmentation and cell death. Indeed, intracellular calcium, detected by fluorescence of fura-2, was elevated in ovarian cells of animals destined to ovulate (controls, 200 mg indomethacin) in comparison to (safeguarded) cells of anovulatory ewes (800 mg indomethacin). These observations provide circumstantial evidence that apical ovarian cell degeneration by calcium-mediated apoptosis is a determinant of follicular instability and rupture, but that these events are unrelated to the gonadotropin-induced rise in prostanoid production characteristic of preovulatory follicles.

Effects of acetylsalicylic acid (aspirin) and naproxen sodium (naproxen) on ovulation, prostaglandin, and progesterone production in the rabbit

OBJECTIVE

To determine the effects of acetylsalicylic acid (aspirin) and naproxen sodium (naproxen) on ovulation, ovarian prostaglandins (PG), and P production in the rabbit via in vivo and in vitro studies.

DESIGN

Aspirin and naproxen were administered i.v. 6.5 and 7 hours, respectively, after hCG administration to New Zealand White adult female rabbits. Laparotomy was performed 24 hours after hCG administration. For in vitro experiments, control animals underwent laparotomy 6.5 (aspirin) and 7 hours (naproxen) after hCG administration. The treated animal received aspirin and naproxen; laparotomy was performed 1 hour later. One ovary was perfused for 6 hours with aspirin or naproxen whereas the contralateral ovary served as a control and was perfused with control medium (M199; GIBCO, Grand Island, New York). Perfusate samples were collected at 1-hour intervals for PG and P determination.

SETTING

A conventional laboratory setting.

INTERVENTIONS

In vivo experiments used i.v. administration of 100 mg/kg aspirin and 10 and 50 mg/kg naproxen. In vitro perfusion was also carried out with 100 micrograms/mL aspirin and 10 and 50 micrograms/mL naproxen added to the perfusate.

MAIN OUTCOME MEASURES

Ovulatory efficiency (no. of ovulations/no mature follicles) and ovarian vein PG and P concentration were determined.

RESULTS

Ovulatory efficiency was 88% for control, 41% for in vivo aspirin-treated, and 40% (10 mg/kg) and 0% (50 mg/kg) for naproxen-treated rabbits. Aspirin and naproxen were associated with decreased ovulatory efficiency when administered in vitro to both in vivo control and in vivo treated ovaries (control-medium = 70%; control-aspirin = 14%; aspirin-medium = 34%; aspirin-aspirin = 0%; control-naproxen = 25%; naproxen-medium = 38%; naproxen = 0% with 10 microgram/mL, and control-naproxen = 13%; naproxen-medium = 0%; naproxen = 0% with 50 micrograms/mL). Prostaglandin F2 alpha was undetectable in the perfusate of those ovaries perfused of those ovaries perfused either with aspirin or naproxen. Ovarian venous concentration of P in the perfusate was similar in all groups.

CONCLUSIONS

Aspirin and naproxen significantly reduced ovulatory efficiency and PG production both in vivo and in vitro in hCG-treated rabbits. A critical period of 6.5 and 7 hours after hCG administration was established.

Different time-course production of peptidic and nonpeptidic leukotrienes and prostaglandins E2 and F2 alpha in the ovary during ovulation in gonadotropin-primed immature rats

Temporal changes in ovarian leukotrienes (LTs) and prostaglandins (PGs) were examined during ovulation to assess roles they may play in this process. Ovulation was induced in immature rats by injection with human chorionic gonadotropin (hCG; 10 IU, s.c.) 2 days after they had been primed with pregnant mare serum gonadotropin (10 IU, s.c.). The ovaries were extirpated at various intervals after hCG administration and assayed for LTB4, and LTC4/D4/E4, as well as PGE2, and PGF2 alpha. Ovarian concentration of LTB4 increased (P < 0.01) rapidly, reaching a peak at 1 hour after hCG administration, then declined (P < 0.05) by 4 hours and remained low thereafter. In contrast, LTC4/D4/E4 peaked (P < 0.01) between 1 and 2 hours, declined (P < 0.05), and then increased (P < 0.01) to achieve a second, larger peak at 10 hours. Prostaglandin E2 increased (P < 0.01) at 6 hours after hCG and did not decrease from the peak value until (P < 0.01) 14 hours after hCG. Concentrations of PGF2 alpha increased (P < 0.01) at 4 hours after hCG, but decreased (P < 0.01) from the peak by 10 hours. Although LTB4, LTC4/D4/E4, PGE2, and PGF2 alpha all increased during ovulation, the time-course differed. This suggests that each eicosanoid may play a distinct role in the process of follicular rupture.

The inhibitory effects of indomethacin, nordihydroguaiaretic acid, and pyrrolidinedithiocarbamate on ovulation and prostaglandin synthesis in yellow perch (Perca flavescens) follicle incubates

This study specifically determined the correlation between ovulation and ovarian prostaglandin F (PGF) and prostaglandin E (PGE) levels in yellow perch follicles treated with several eicosanoid synthesis inhibitors. In incubates treated with indomethacin (IM; .00001 to 10.0 micrograms/ml) there was a significant dose-dependent correlation between ovulation and PGF/PGE levels, and between the two prostaglandins (PGs), further implicating PGs in the control of yellow perch ovulation. In incubates treated with nordihydroguaiaretic acid (NDGA), a traditional lipoxygenase inhibitor, there was a significant correlation between ovulation and PGF levels, yet there was no correlation between PGE levels and ovulation. A free-radical scavenger, pyrrolidinedithiocarbamate (PDTC) inhibited ovulation in a dose-dependent manner yet there was no correlation between either PGF or PGE levels and this inhibition, indicating that PDTC may block ovulation at other steps that involve free-radicals.

Prostaglandins in the ovary and fallopian tube

More than 20 years following the recognition of a possible role for eicosanoids in ovarian function a physiological role for prostaglandins and/or leukotrienes in human ovulation, corpus luteum function and tubal motility remains to be demonstrated. With respect to ovarian function, the well-characterized preovulatory rise in eicosanoid production in animal species and humans, in conjunction with the large body of experimental evidence employing inhibitors of prostaglandin synthesis and replacement of individual prostaglandins, has provided strong evidence for a role in follicular rupture independent of other LH-mediated ovulatory events. The possible mechanism of prostaglandin-induced follicle rupture may involve stimulation of proteolytic activity via substances such as plasmin and PA; however, this is controversial. A role for prostaglandins in ovarian luteal function is well established in laboratory animals and large ruminant species, where PGF2 alpha derived from the uterus has been demonstrated to be the luteolytic factor. In humans, luteal function may be influenced by local intraovarian eicosanoid production, which has been suggested to involve the paracrine interaction of local ovarian hormones such as oxytocin, noradrenaline, insulin and IGFs, to name but a few. Several lines of evidence have also implicated prostaglandins as an aetiological factor in ovarian pathological states such as seen in the OHSS. However, the bulk of clinical experimental evidence to date has failed to support this contention. Prostaglandin production has likewise been well characterized in the fallopian tube in both humans and animal species. Whereas a role for prostaglandins in tubal transport has been demonstrated with animal species such as the rabbit, several studies have failed to define a similar function in humans. More recently, direct injections of prostaglandin analogues into the fallopian tube and the corpus luteum have been shown to be efficacious as a treatment for ectopic pregnancy. Whether the primary mechanism of action involves effects on tubal musculature or corpus luteum function, or is simply a local vascular effect, remains to be demonstrated. Therefore, although the physiological role for eicosanoids in ovarian and tubal function remains unclear, particularly in the human, an increasing body of recent evidence has suggested an important paracrine function for this class of cellular mediators whose interaction with other more recently characterized local ovarian factors has only begun to be recognized.

Inhibition of ovulation in the gonadotropin-primed immature rat by exogenous prostaglandin E2

In the past two decades there have been innumerable reports that prostaglandins (PGs) are essential for mammalian ovulation. However, we have recently found that a relatively low dose of 0.03 mg indomethacin (INDO) sc to PMSG/hCG-primed immature Wistar rats can significantly reduce ovarian PG levels without inhibiting the control ovulation rate of 60+ ova/rat (1-3). In view of this information, the present study was an effort to duplicate the earlier reports that PGs can reverse the "inhibitory" effect of INDO on ovulation. In control animals, which received PMSG and hCG only, the ovulation rate was 63.8 +/- 4.5 ova/rat. This rate was reduced to 4.1 +/- 1.1 ova/rat when the animals were injected with 1.0 mg INDO at 3 h after hCG. In no instance was this inhibition reversed when the animals were treated with 1.0 mg of PGE2 or PGF2 alpha, or a combination of both prostanoids in either a single dose at 3 h after hCG, or in 4x doses at 2-h intervals beginning at 3 h after hCG. Furthermore, in animals that did not receive INDO, the ovulation rate in PGE2-treated animals was reduced to 20.0 +/- 6.7 ova/rat, and in animals treated with PGE2 and PGF2 alpha (combined) it was reduced to 19.4 +/- 6.5 ova/rat. In summary, not only did the PGs fail to reverse the anti-ovulatory effect of INDO, PGE2 actually suppressed the ovulation rate.

Comparison of inhibitory actions of indomethacin and epostane on ovulation in rats

Indomethacin, an inhibitor of cyclooxygenase that generates prostaglandins (PGs) from arachidonic acid, and 2 alpha,4 alpha,7-4,5-epoxy-17-hydroxy-4,17-dimethyl-3-oxoandrostane- 2-carbonitrile (epostane), an inhibitor of 3 beta-hydroxysteroid dehydrogenase that generates progesterone from pregnenolone, are both potent inhibitors of ovulation. This report compares the dose-dependent effects of these two inhibitors on ovarian levels of 5-, 12-, and 15-hydroxyeicosatetraenoic acid methyl ester (HETEs), prostaglandin E2 (PGE), prostaglandin F2 alpha (PGF), progesterone, 17 alpha-hydroxyprogesterone, 17 beta-estradiol, 4-androstene-3,17-dione, and testosterone during ovulation in 25-day-old immature Wistar rats. The ovulatory process was initiated by 10 IU of human chorionic gonadotropin (hCG). Indomethacin was given at 3 h after hCG in doses ranging from 0.0316 to 10.0 mg/rat. A dose of 0.1 mg/rat was the lowest dose to significantly reduce the ovulation rate from the control level of 70.5 +/- 5.8 ova/rat. This dose also reduced 15-HETE, but not 5-HETE, 12-HETE, or the steroids. PGE and PGF were strongly inhibited by an even lower dose of indomethacin (0.0316 mg/rat), but this dose did not affect the ovulation rate. Epostane was given at 3 h after hCG in doses ranging from 0.1 to 5.0 mg/rat. A dose of 1.0 mg/rat was the lowest dose to significantly inhibit ovulation. This dose also reduced the ovarian levels of 15-HETE and progesterone but not 5-HETE, 12-HETE, PGE, PGF, or the other steroids. The results indicate that the ovulation rate is most closely correlated to ovarian 15-HETE levels.

Ovarian hydroxyeicosatetraenoic acids compared with prostanoids and steroids during ovulation in rats

Hydroxyeicosatetraenoic acid methyl esters (HETEs) are lipoxygenase products of arachidonic acid that are generated along with prostaglandins (PGs) during acute inflammatory reactions. Whereas it is well known that ovarian PG levels increase during the ovulatory process, little is known about ovarian HETEs. This report compares the ovarian changes in 5-, 12-, and 15-HETE with ovarian PGE and PGF, along with progesterone, 17 alpha-hydroxyprogesterone, 4-androstene-3,17-dione, testosterone, and 17 beta-estradiol. Ovulation was induced in immature Wistar rats by sequential treatment with pregnant mare's serum gonadotropin and human chorionic gonadotropin (hCG). Follicles began rupturing 10 h after hCG treatment. The greatest correlation was among 12-HETE, 15-HETE, and progesterone, which increased to peak levels at 10 h after hCG. In contrast, the ovarian levels of 5-HETE, 17 alpha-hydroxyprogesterone, testosterone, and 17 beta-estradiol all declined sharply beginning 4 h after hCG. 2 alpha,4 alpha,7-4,5-Epoxy-17-hydroxy-4,17-dimethyl-3-oxo-androstane-2- carbonitrile (epostane), a potent inhibitor of steroid synthesis and ovulation, sharply reduced the synthesis of all five steroids within 30 min after its injection at 3 h after hCG. Among the five eicosanoids, epostane mainly inhibited 15-HETE. The results suggest that 15-HETE, along with progesterone, may have an important role in ovulation.

Increased production of ovarian thromboxane in gonadotropin-treated immature rats: relationship to the ovulatory process

Thromboxane (TX) B2, a stable metabolic product of hydrolysis of TXA2, was measured by radioimmunoassay in tissue extracts of ovaries of immature rats pretreated with pregnant mare's serum gonadotropin and human chorionic gonadotropin. Ovarian concentrations of TXB2 increased before, and remained elevated after, the time of ovulation. In a subsequent study, ovulation was inhibited in a dose-dependent fashion by a reported TXA2 receptor antagonist, AH23848. Nevertheless, inhibition of the preovulatory rise in synthesis of TXB2 by furegrelate (a thromboxane synthetase inhibitor) did not prevent ovulation. Nor was the blockade of ovulation caused by indomethacin (a cyclooxygenase inhibitor) reversed by a TXA2 mimetic (U-46619). It does not appear that a preovulatory increase in ovarian thromboxane is an obligatory component of the ovulatory mechanism of gonadotropin-primed immature rats.

Effect of indomethacin, cycloheximide, and aminoglutethimide on ovarian steroid and prostanoid levels during ovulation in the gonadotropin-primed immature rat

It has become popular to use the gonadotropin-primed immature rat to study ovulation. The ovarian content of progesterone, estradiol, PGE2, PGF2 alpha, and 6-keto-PGF1 alpha during the ovulatory process was determined in this model. Also, the effect of three anti-ovulatory agents on the ovarian levels of the above substances was determined. At 23 days of age, Wistar rats were primed with pregnant mares serum gonadotropin (PMSG) sc, and two days later the ovulatory process was initiated with human chorionic gonadotropin (hCG) sc. The ovarian follicles began rupturing 12 h later. Ovaries were assayed for the two steroids and prostanoids at 2-h intervals before and several 4-h intervals after ovulation. The ovarian estradiol level increased slightly between 0 and 2 h after hCG, while the progesterone level increased sharply between 2 and 4 h after hCG--at a time when the estradiol declined markedly. All three prostanoids increased concomitantly with progesterone. When the PG synthesis was blocked by indomethacin treatment at 1 h before hCG, ovarian progesterone levels still increased. In contrast, when steroidogenic activity was inhibited by aminoglutethimide, the ovarian prostanoid levels also decreased. Cycloheximide had little effect on the steroids and prostanoids. It is concluded that ovarian prostanoid synthesis might be influenced by ovarian steroid output.