Ovulation block by indomethacin, an inhibitor of prostaglandin synthesis: a study of its site of action in rats

Collaborative work on evaluation of ovarian toxicity. 12) Effects of 2- or 4-week repeated dose studies and fertility study of indomethacin in female rats

2-week and 4-week general toxicity studies of indomethacin, a nonselective inhibitor of cyclooxygenase 1 and 2, were performed using rats. A female fertility study was also conducted to compare the results to those of ovarian histopathological findings. The main purposes of the present studies are to assess whether a precise histopathological examination, taking the morphological changes the female reproductive organs undergo during each estrus phases into account, can evaluate toxicity to the ovaries, and to determine the optimal administration period for detecting ovarian toxicity. Indomethacin was administered on a daily basis to female Sprague-Dawley rats at doses of 0, 0.4, 1.3, or 4 mg/kg in the both the general toxicity studies and the female fertility study. In the general toxicity studies, unruptured follicles or luteinized cysts were observed histopathologically in the 4 mg/kg group in both the 2-week and 4-week studies. In addition, follicular cysts were found in the 4 mg/kg group in the 4-week study. Estrous cyclicity was not disturbed in both studies. There were no histopathological changes in the ovaries of the 1.3 mg/kg group in general toxicity studies. In the female fertility study, no toxic effects on female fertility parameters were detected in the 0.4 and 1.3 mg/kg group treated with indomethacin, but 8 of 10 rats in the 4 mg/kg group died or were sacrificed before completion of the dosing period. These results demonstrated that 2 weeks of indomethacin treatment is sufficient to detect unruptured follicles or luteinized cyst in the ovary. In addition, 4 weeks of dosing maybe required for induction of follicular cysts, although we could not clearly show that these histopathological changes would affect female fertility functions. These present studies suggest that a precise histopathological examination may be able to predict the effect of test articles on female reproductive functions.

Effects of indomethacin on the selective release of follicle-stimulating hormone during the period of ovulation in the rat

To determine whether indomethacin, a potent inhibitor of prostaglandins endoperoxide synthetase, affects the selective follicle-stimulating hormone (FSH) surge during the period of ovulation, the compound was administered intravenously (i.v.), concurrent with 10 IU human chorionic gonadotropin (hCG), to diestrous female rats at 16:00 hr. Indomethacin inhibited the number of ovulations in a dose-dependent manner, and treatment with 500 micrograms indomethacin reduced number of oocytes in the ampullae most effectively without enteric lesions. In the histological observation, oocytes that had began to mature were found not only in unruptured luteinized follicles but also in ovarian interstitium beneath ruptured luteinized follicle. Despite the inhibitory effects of indomethacin on ovulation, peri-ovulatory FSH and progesterone surges occurred in comparable levels and duration to vehicle-treated animals. These results indicate that indomethacin-induced inhibition of prostaglandin synthesis does not affect the selective release of FSH during the peri-ovulatory period.

A role of prostaglandin in the secretion of inhibin and oestradiol-17 beta in equine chorionic gonadotrophin-primed rats

The role of prostaglandins in the secretion of inhibin and oestradiol-17 beta was examined in immature female rats treated with equine chorionic gonadotrophin. Administration of prostaglandin (PG) F2 alpha to animals whose serum and ovarian levels of inhibin and oestradiol-17 beta had been suppressed by indomethacin given 24 h after equine chorionic gonadotrophin prevented the inhibition or restored the levels to normal. Initiation of PGF2 alpha replacement immediately after treatment with indomethacin was more effective. The results are consistent with the hypothesis that PGs play a regulatory role in the synthesis and secretion of inhibin and oestradiol-17 beta by the rat ovary.

Inhibition of the first ovulation and ovarian prostaglandin F2 alpha metabolism by danazol in rats

The present study was conducted to investigate the mode of action of danazol by monitoring the first ovulation, serum luteinizing hormone (LH) levels and ovarian prostaglandin (PG) F2 alpha metabolism in pregnant mare serum gonadotropin (PMSG)-primed immature female rats. When danazol (750 mg/kg) was given p.o. once a day for 5 days (day 24-28), the occurrence of the first ovulation, the increase in capacity to form 13,14-dihydro-PGF2 alpha and PGF2 alpha levels induced by PMSG (5 IU) injected on day 26 were clearly inhibited on day 29. Danazol also markedly suppressed the LH surge occurring on day 28. Although the danazol-induced blockage of ovulation was restored by injection of human chorionic gonadotropin, the number of oocytes was significantly decreased as compared with that of controls. The present data indicate that the inhibitory actions of danazol on ovulation and ovarian PGF2 alpha metabolism may occur via some direct effects on the ovary in addition to the suppression of gonadotropin release from the pituitary gland.

Relationship between the production capacity of ovarian 13,14-dihydro-prostaglandin F2-alpha and the process of ovulation in immature female rats pretreated with gonadotropin

The purpose of this work was to investigate the effects of gonadotropin on the production capacity of ovarian 13,14-dihydro-prostaglandin F2-alpha (13,14H2-PGF2 alpha) and whether or not this capacity had any relation to the process of ovulation in rat. To induce the first ovulation, immature rats were injected subcutaneously with PMSG (5 IU/rat) at 8:00 at 26 days of age and some of these rats were followed by an intraperitoneal injection of hCG (10 IU/rat) at 57 hrs after PMSG treatment. The 13,14H2-PGF2 alpha production capacity was unchanged as compared with vehicle control until 57 hrs after PMSG treatment. However, the capacity showed a striking increase at 60 hrs after PMSG treatment. A maximal increase of about 7 fold was observed at 9 hrs after hCG injection just before ovulation. The production capacity of the Graafian follicle (GF) and the part (WO-GF) of the whole ovary (WO) from which the GF is removed at 2:00 on day 29 and the capacity of early corpus luteum at 8:00 on day 29 was greater than that of GF and WO-GF at 0:00 on day 29. These results suggest that the 13,14H2-PGF2 alpha production capacity in rat ovary is regulated by gonadotropin and is closely associated with the process of ovulation.

Mode of action of chlorpromazine (CPZ) blockage on 13,14-dihydroprostaglandin F2-alpha formation in rat ovary

The mode of action of the inhibitory effect of CPZ on 13,14-dihydroprostaglandin F2-alpha (13,14H2-PGF2-alpha) formation in rat ovary was examined. The inhibition of 13,14H2-PGF2-alpha formation and of ovulation induced by a proestrus were completely recovered by an injection of hCG (25 IU/rat) or LH-RH (500 ng/rat) at 15:00 on the same day. 13,14H2-PGF2-alpha formation and ovulation were not inhibited by a single injection of prolactin (PRL:6 IU/rat) at 13:00 on the day of proestrus. Repeated injection of PRL inhibited cyclic ovulation and 13,14H2-PGF2-alpha formation. The estrus cycle of PRL treated animals showed a continuous state of diestrus. Although 13,14H2-PGF2-alpha formation and ovulation were inhibited by the repeated injection of CPZ, the repeated-simultaneous injection of CPZ and bromocriptine at 10:00 once a day for 3 days from the first day of diestrus partly restored both and entirely reversed the suppression of the cyclic-changes in the in the vaginal smear pattern. These results indicate that the inhibition of 13,14H2-PGF2-alpha formation induced by a single injection of CPZ probably occurs via the suppression of LH-RH release from the hypothalamus, whereas PRL secretion may participate in the inhibitory effects of repeated injections of CPZ.

Reproductive studies with the anti-inflammatory agent, piroxicam: modification of classical protocols

Reproductive toxicology studies were conducted in rabbits and rats given piroxicam, a non-steroidal anti-inflammatory agent (NSAI), orally at 2, 5 and 10 mg/kg/day. In teratology studies there was neither drug-related embryotoxicity nor teratogenicity. As piroxicam, like other NSAI, affects parturition in rats and leads to a progressive toxicity in lactating females, standard protocols were modified: dams of the female fertility study were treated from 2 weeks prior to mating until day 6 of gestation and females of the post-natal toxicity study were treated from parturition until day 12 of lactation. No other adverse effects on reproduction, fertility and postnatal development were observed.

Prostaglandins and preovulatory follicular maturation in mice

Experiments have been carried out in an effort to reverse the indomethacin-induced inhibition of preovulatory follicular development in immature superovulated mice utilizing prostaglandins E2 and F2 alpha. All mice were primed with 5 IU pregnant mare's serum gonadotropin followed 40 h later by 80 IU luteinizing hormone (LH). Animals were sacrificed 10 1/2 or 11 1/2-12 h post-LH, at which time ovaries were fixed and prepared for microscopic observation. Control mice receiving both indomethacin and prostaglandin (PG) vehicles averaged 92% germinal vesicle breakdown, and 82% of maturing oocytes were surrounded by an expanded cumulus oophorus. Ovarian weight increased by 29% and the apical walls of preovulatory follicles demonstrated appreciable thinning following LH administration. In mice receiving indomethacin plus PG vehicle, follicular maturation was suppressed in a dose-dependent manner; in mice receiving 10 mg/kg, less than 50% of the oocytes resumed meiosis and, of these, only 9% were accompanied by cumulus expansion. Ovarian weight gain was also inhibited, and the apical follicle wall exhibited few signs of preovulatory thinning. PGE2 and PGF2 alpha both reversed the inhibition of cumulus and oocyte maturation induced by indomethacin, though PGE2 was more effective. Only PGF2 alpha promoted apical follicular thinning, and neither PG had a significant effect on ovarian weight. We conclude that, in mice, PGs may play an integral role during preovulatory maturation of the oocyte and cumulus, as well as thinning of the apical wall.

Induction of ovulation and spawning in the catfish, Clarias batrachus (L.) by prostaglandin F2 alpha

Administration of low doses of prostaglandin F2 alpha (PGF2 alpha), i.e. 10 and 100 ng/g b.wt, was ineffective in inducing ovulation and spawning in mature catfish. However, doses of 200 ng/g b.wt of PGF2 alpha elicited partial response, and 500 ng/g b.wt of PGF2 alpha induced profuse ovulation and spawning similar to that induced by administration of human chorionic gonadotropin (HCG).

Inhibition of ovulation by indomethacin in rats

Indomethacin, a specific prostaglandin synthetase inhibitor, was found to block ovulation in rats when scheduled at 1200h on day 4 of the cycle. The same regimen was ineffective at 1800h, but its antiovulatory efficacy was estimated to be about 50% when given at 1600h. An injection of indomethacin given concurrently with prostaglandin F2a allowed ovulation in 80% of the test animals. None of the animals, irrespective of the drug schedule, became pregnant on mating with the fertile males but showed a remarkable decidual cell reaction (DCR) in response to unilateral uterine traumatization. The anti-ovulatory or intinidation effect of indomethacin is discussed.

Effects of indomethacin on preovulatory follicles in immature, superovulated mice

In order to demonstrate the possible role of prostaglandins in preovulatory follicular development, immature mice superovulated with pregnant mare serum followed 40 hours later by luteinizing hormone (LH) were treated with the prostaglandin-synthetase inhibitor, indomethacin. Indomethacin (10 mg/kg) injected at varying intervals prior to or following LH inhibited ovulation most effectively when administered within 2 hours of the ovulatory gonadotropin. This inhibition was accompanied by (1) suppression of the morphological changes normally occurring within the follicular wall during preovulatory development and (2) failure of germinal vesicle breakdown (GVBD) in two-thirds of the follicles examined. When GVBD occurred, indomethacin treatment appeared to delay meiotic maturation. Cumulus tissue was more compact than in control follicles and maintained a close association with the oocyte. These results suggest that alterations in the morphology of the follicle prior to ovulation--specifically, thinning of the apical follicular wall and meiotic maturation--are regulated by prostaglandins.

The effect of prostaglandin synthesis inhibition by indomethacin on ovulation and ovum maturation in the in vitro perfused rabbit ovary

Prostaglandins (PGs) have been implicated in the mechanism of ovulation in several species through the use of PG synthesis inhibitors such as indomethacin. Studies of ovulation in the in vitro perfused rabbit ovary have aided in the delineation of the process of ovulation. This study was designed to determine the effects of indomethacin on follicle rupture and ovum development in the in vitro perfused rabbit ovary preparation. Indomethacin treatment (0.5 microgram/ml) significantly reduced the occurrence of ovulation in gonadotropin-treated ovaries. The percentage of in vitro ovulated ova and ova recovered from unruptured follicles during ovarian perfusion which achieved Metaphase II did not significantly differ between indomethacin-treated and control ovaries (hCG alone). However, increased degeneration of Metaphase II ova was associated with indomethacin treatment. In in vitro culture experiments this degeneration could be prevented by supplemental PGF2 alpha. These results indicate that inhibition of PG synthesis by indomethacin prevents follicle rupture but does not affect ovum maturation, thus providing further evidence that these two processes are distinct phenomena in vitro.

Inhibition of superovulation in immature female rats by the antiserum to cyclooxygenase

In order to investigate involvement of prostaglandins (PGs) in ovulation, we examined whether the antiserum to cyclooxygenase was able to inhibit superovulation in immature female rats as indomethacin did. The antiserum to cyclooxygenase was raised in rabbits using as antigen the solubilized cyclooxygenase extracted and purified from bovine seminal vesicles. The in vivo administration of the antiserum inhibited superovulation in female rats dose-dependently at doses of 0.1, 0.2 and 0.4 ml but did not affect production of progesterone. Inhibition of cyclooxygenase in the follicular cells due to the antiserum causing no effect on steroidogenesis was observed in organ cultures of the follicles excised from rats primed with PMS-hCG and the antiserum. In contrast to this, no inhibition of cyclooxygenase was detected upon adding the antiserum to the culture medium. The present study showed PG is as indispensable a factor in ovulation as are the steroids.

Inhibition of ovulation and fertilization by indomethacin and effect of prostaglandin-F2 alpha on early pregnancy in the rabbit

Ovulation induced by HCG in rabbits was blocked by a single subcutaneous injection of 6 mg/kg indomethacin given 6 h after the insemination and HCG treatment. In addition, a time-dependent inhibition in the fertilization rate after indomethacin treatment was also recorded. This suggests that indomethacin, when given at a critical time and at an appropriate dose level, not only blocks ovulation but also interferes with fertilization. Treatment with graded amounts of prostaglandin-F2 alpha incorporated in a Silastic-polyvinylpyrrolidone-gel (PVP) had marginal to no effect after intravaginal placement on 4- or 6-day pregnancy. However, 5 mg PGF 2 alpha/ Silastic-PVP tube when placed intravaginally on Day-7 of pregnancy resulted in termination of pregnancy in 66% of the treated does. This implies that young corpora lutea are resistant of PGF2 alpha treatment and that pregnancy at the time of ovo-implantation can be terminated by PGF2 alpha incorporated in a Silastic-PVP tube.

Spontaneous and prostaglandin- or oxytocin-induced motility of rat ovaries isolated during different stages of the estrous cycle: effects of norepinephrine

Ovaries isolated from rats in different stages of the sex cycle were explored for spontaneous or drug-induced contractile activity. The number of spontaneously active ovaries as well as the magnitude of the isometrically developed tension and frequency of contractions were greater during the periovulatory interval (late proestrus and estrus) than during early proestrus or metestrus. Furthermore, during estrus or late proestrus the left ovaries exhibited a mechanical activity significantly greater than that of the right ovaries. The oxytocin-triggered motility was clearly more marked immediately prior to ovulation (late proestrus) and greater in left ovaries than in right ovaries. In contrast, the contractions induced by prostaglandin F2alpha were similar during early proestrus and late proestrus. Ovarian contractile reactivity to norepinephrine indicated the presence in the tissue of alpha- and beta-adrenergic receptors. During early proestrus this agent stimulated the motility of left and right ovaries, whereas close to the ovulatory interval (late proestrus) it depressed the contractions of left ovaries. This last influence was blocked by propranolol. The existence of a close relationship between ovarian contractile activity and ovulation is reinforced by the present results in the rat. A tentative participation of oxytocin is also suggested. In addition, the influences of other possible regulatory agents of ovarian contraction, such as catecholamines and prostaglandins, are presented and discussed.

In vitro ovulation of trout oocytes: effect of prostaglandins on smooth muscle-like cells of the theca

Ovulation (active expulsion of oocyte from the mature follicle) of trout follicles matured in vivo can be induced in vitro by adding PGF2alpha at doses of 1 and 5 mug/ml. PGE2 is ineffective. The in vitro induction of ovulation by PGF2alpha is inhibited in a calcium free medium or by inhibitors of calcium influx, particularly by Mn++ and La+++, suggesting the ovulation process implies active contraction of the smooth muscle cells of the theca. A significant but partial inhibition is also observed with cytochalasin B (1 and 5 mug/ml) demonstrating that contraction of other cell types than muscle, containing actin-like filaments, may also participate in the process.

Effects of indomethacin and prostaglandins on ovulation of goldfish

A technique is described whereby elevated temperature and HCG injection yield a high percentage of ovulation in gravid goldfish. Indomethacin (10 mug/g; i.p. injection) completely inhibits ovulation if given within 6 hours following HCG (4 IU/g); the unovulated oocytes develop rapidly into corpora atretica. PGE1, PGE2, and PGF2alpha (5 mug/g; i.p. injection) induce ovulation in fish treated with indomethacin and HCG; PGE2 was most effective when given 11 hours after HCG. The results suggest that the ovulatory action of prostaglandins following HCG stimulation is at the level of the ovary and that it is restricted to a period between 7 and 12 hours after the gonadotropin injection.

Influence of prostaglandin F autoantibodies on the estrous cycle of the guinea pig

Adult female guinea pigs were actively immunized with prostaglandin F-2alpha conjugated to bovine serum albumin (BSA). Control animals, immunized against BSA continued to cycle normally, while the animals immunized against prostaglandin F-2alpha stopped cycling after one to three normal cycles. Laparotomy at 30 days after the last estrus revealed no recently formed corpora lutea. During the remaining 70 days of observation the antibody titer increased to 1:700, accompanied by increasing total serum estrogens (136 pg/ml at day 100) and a slow decline in circulating progesterone levels (0.6 ng/ml at day 100). The ovaries at day 100 contained degenerated corpora lutea and luteinized follicles. The suppression of the estrous cycle in the present experiments was interpreted as resulting from prolongation of luteal function as well as from inhibition of ovulation.