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PubMed1997

Differential effects of gonadotropin and orthovanadate on oocyte maturation, ovulation, and prostaglandin synthesis by Rana ovarian follicles in vitro.

Effects of gonadotropin and sodium orthovanadate on oocyte maturation, ovulation, prostaglandin, and progesterone synthesis were examined during in vitro culture of Rana ovarian follicles obtained from hibernating animals. Frog pituitary homogenates (FPH, 0.05 gland/ml) effectively induced oocyte maturation (germinal vesicle breakdown, GVBD) and ovulation (> 90%) in ovarian follicles obtained in mid-hibernation (mid-December through late January). In contrast, orthovanadate induced a limited amount (< 45%) of ovulation of some oocytes without concomitant induction of maturation during mid-hibernation. In late hibernation (February to early March), considerable spontaneous maturation and ovulation occurred in cultured ovarian follicles. During this period both FPH (0.0005-0.05 gland/ml) or orthovanadate (0.01-1 mM) treatment markedly increased the incidence of ovulation and accelerated the onset of ovulation in a dose dependent manner. When examined after 12 h of culture, few (< 5%) oocytes ovulated in response to orthovanadate had undergone GVBD whereas most (> 90%) of those ovulated in response to FPH had matured. However, the majority of oocytes ovulated (72%) within 6 h of exposure to FPH had intact GVs, indicating that GVBD is also not a prerequisite for ovulation induction in response to FPH. Orthovanadate stimulated PGF2 alpha in a dose dependent manner but failed to stimulate progesterone production whereas FPH stimulated secretion of both PGF2 alpha and progesterone. The amount and time course of PGF2 alpha secretion in response to orthovanadate were similar to results produced with FPH stimulation. Treatment of PGF2 alpha to follicles obtained in late hibernation also accelerated the ovulation of the oocytes. Taken together, the data suggest that orthovanadate enhanced ovulation of immature oocytes was mediated via enhanced PGF2 alpha production and that oocyte maturation is not essential or prerequisite for in vitro oocyte ovulation in Rana.

Animals↗
PubMed1994

Homeotic Transformation of Ovules into Carpel-like Structures in Arabidopsis.

Ovules are specialized reproductive organs that develop within the carpels of higher plants. In Arabidopsis, mutations in two genes, BELL1 (BEL1) and APETALA2 (AP2), disrupt ovule development. In Bel1 ovules, the inner integument fails to form, the outer integument develops abnormally, and the embryo sac arrests at a late stage of megagametogenesis. During later stages of ovule development, cells of the outer integument of a Bel1 ovule sometimes develop into a carpel-like structure with stigmatic papillae and second-order ovules. The frequency of carpel-like structures was highest when plants were grown under conditions that normally induced flowering and was correlated with ectopic expression in the ovule of AGAMOUS (AG), an organ-identity gene required for carpel formation. Together, these results suggested that BEL1 negatively regulates AG late in ovule development. Likewise, mutants homozygous for the strong AP2 allele ap2-6 sometimes displayed structures with carpel-like features in place of ovules. However, such abnormal Ap2 ovules are much less ovulelike in morphology and form earlier than the Bel1 carpel-like structures. Because one role of the AP2 gene is to negatively regulate AG expression early in flower development, it is possible that AP2 works in a similar manner in the ovule. A novel ovule phenotype observed in Bel1/Ap2-6 double mutants suggested that BEL1 and AP2 genes function independently during ovule development.

Journal Article↗
PubMed1982

Fertility after childbirth: infant feeding patterns, basal PRL levels and post-partum ovulation.

The infant feeding patterns at the time of first ovulation after childbirth were determined in a longitudinal study of twenty-seven mothers who chose to breast feed their babies. Fourteen mothers suppressed ovulation throughout lactation and thirteen ovulated while still breast feeding. Those who ovulated while breast feeding had all introduced two or more supplementary feeds/day, reduced suckling frequency to less than six times/day and reduced suckling duration to less than 60 min/day at the time of first ovulation. Basal PRL levels had fallen to below 600 microunits/l in all but one of the mothers at first ovulation. Those mothers who suppressed ovulation for more than 40 weeks post-partum (late ovulation group) were compared with those who ovulated between 30 and 40 weeks post-partum (middle group) and with those who ovulated before 30 weeks post-partum (early group). The late ovulation group breast-fed for longest, suckled most intensively, maintained night feeds for longest and introduced supplementary feeds most gradually. This study suggests suckling may be the most important factor inhibiting the return of ovulation during lactation and that policies which encourage increased suckling frequency and duration will maximize the contraceptive effects of breast feeding.

Adult↗
PubMed1997

Number of ovulations in the marmoset monkey (Callithrix jacchus): relation to body weight, age and repeatability.

The relation between number of ovulations and body weight, age or maternal identity was examined in 69 ovarian cycles from 29 captive-born common marmoset monkeys (Callithrix jacchus). Specifically, we addressed the following questions: was there high repeatability of ovulation number? Most of the variation in ovulation number was within, rather than between subjects. Repeatability in number of ovulations was 0.081 (n = 20 females with 2-6 ovulatory cycles per female); was age related to number of ovulations? There was no relation between age and number of ovulations, either within or between subjects; and was weight related to number of ovulations? Weight was related to number of ovulations. When the relation between number of ovulations (1-2 versus 3-4) and weight was examined through a logistic regression, there was a significant relation. Also, of the 11 subjects which had a variable number of ovulations across cycles, 90.9% were heavier when ovulating 3-4 than when ovulating 2. These results are discussed as the basis for the proposal that callitrichid primates may have been selected for potential variation in reproductive output and that this variation may be related to energy availability.

Age Factors↗
PubMed1995

Ovulated oocytes collected from PMSG/hCG-treated and cycling Djungarian or Siberian hamsters (Phodopus sungorus) are structurally similar with no evidence of polar body formation, indicating arrest in meiosis I.

This study was undertaken (1) to devise a method of inducing multiple follicular development and subsequent ovulation in the Djungarian or Siberian hamster (Phodopus sungorus) and (2) to assess the quality of ovulated oocytes collected from PMSG/hCG treated animals in comparison to naturally ovulating animals. Hamsters (4-5 weeks; n = 70) received 5 IU PMSG followed 50-52 hr later by 10 IU hCG. Ovulated oocytes were collected 14-20 hr after hCG injection. Ovulated oocytes were flushed from oviducts of cycling animals (7-12 weeks; n = 30) exhibiting two consecutive estrous cycles. Oocytes were fixed and subjected to triple fluorescence immunostaining using anti-tubulin antibodies, fluorescein phalloidin, and Hoechst 33258. The mean number of ovulated oocytes collected from cycling animals was 4.8 +/- 0.4 (range 1-7). Ovulation occurred in 73% of the PMSG/hCG-stimulated animals. The mean number of oocytes ovulated from stimulated animals was 9.2 +/- 0.8 (range 0-22). The ovaries of animals that did not ovulate or that ovulated few oocytes did respond to PMSG, as indicated by the presence of multiple follicular development and pre-ovulatory stigmata. There was no evidence of a polar body in ovulated oocytes collected from PMSG/hCG-treated or cycling animals, indicating that oocytes were arrested in meiosis I. In the majority (80%) of ovulated oocytes from PMSG/hCG-treated and cycling animals, cortically placed chromosomes were aligned on a metaphase plate equidistant from a bipolar spindle. Sparse f-actin staining was observed in the region of the ooplasm surrounding the chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Neuroendocrine regulation of GnRH release in induced ovulators.

GnRH is the key neuropeptide controlling reproductive function in all vertebrate species. Two different neuroendocrine mechanisms have evolved among female mammals to regulate the mediobasal hypothalamic (MBH) release of GnRH leading to the preovulatory secretion of LH by the anterior pituitary gland. In females of spontaneously ovulating species, including rats, mice, guinea pigs, sheep, monkeys, and women, ovarian steroids secreted by maturing ovarian follicles induce a pulsatile pattern of GnRH release in the median eminence that, in turn, stimulates a preovulatory LH surge. In females of induced ovulating species, including rabbits, ferrets, cats, and camels, the preovulatory release of GnRH, and the resultant preovulatory LH surge, is induced by the receipt of genital somatosensory stimuli during mating. Induced ovulators generally do not show "spontaneous" steroid-induced LH surges during their reproductive cycles, suggesting that the positive feedback actions of steroid hormones on GnRH release are reduced or absent in these species. By contrast, mating-induced preovulatory surges occasionally occur in some spontaneously ovulating species. Most research in the field of GnRH neurobiology has been performed using spontaneous ovulators including rat, guinea pig, sheep, and rhesus monkey. This review summarizes the literature concerning the neuroendocrine mechanisms controlling GnRH biosynthesis and release in females of several induced ovulating species, and whenever possible it contrasts the results with those obtained for spontaneously ovulating species. It also considers the adaptive, evolutionary benefits and disadvantages of each type of ovulatory control mechanism. In females of induced ovulating species estradiol acts in the brain to induce aspects of proceptive and receptive sexual behavior. The primary mechanism involved in the preovulatory release of GnRH among induced ovulators involves the activation of midbrain and brainstem noradrenergic neurons in response to genital-somatosensory signals generated by receipt of an intromission from a male during mating. These noradrenergic neurons project to the MBH and, when activated, promote the release of GnRH from nerve terminals in the median eminence. In contrast to spontaneous ovulators, there is little evidence that endogenous opioid peptides normally inhibit MBH GnRH release among induced ovulators. Instead, the neural signals that induce a preovulatory LH surge in these species seem to be primarily excitatory. A complete understanding of the neuroendocrine control of ovulation will only be achieved in the future by comparative studies of several animal model systems in which mating-induced as well as spontaneous, hormonally stimulated activation of GnRH neurons drives the preovulatory LH surge.

Animals↗
PubMed2005

Effects of external pH on hormonally regulated ovarian follicle maturation and ovulation in Atlantic croaker.

In vitro studies of ovarian follicle maturation and ovulation in teleost fishes typically are conducted within a narrow range (7.5-7.8) of constant external (medium) pH, although there is evidence that pH can influence ovulation. Therefore, this study with Atlantic croaker investigated the effects of external pH on hormonally regulated in vitro maturation and ovulation as well as changes in the pH of ovarian fluid during in vivo maturation and ovulation. For the in vitro experiments, follicles were first incubated with human chorionic gonadotropin (hCG) to induce maturational and ovulatory competencies, and then with maturation-inducing hormone (MIH) to induce completion of maturation and ovulation. At a constant external pH within the range of 7.0-8.2, the lower pH levels (7.0-7.3) generally inhibited or slowed down hormonally induced maturation and ovulation whereas higher pH (7.6-8.2) facilitated these processes. When ovarian follicles were incubated at a constant pH of 7.6 during the priming incubation with hCG, changing the external pH during the incubation with MIH had relatively little effect on oocyte maturation or ovulation. Thus, the inhibitory effect of constant low levels of external pH (7.0-7.3) on maturation and ovulation may be primarily due to disruptions in the gonadotropin-dependent acquisition of maturational and ovulatory competencies. The pH of ovarian fluid remained constant at 8.5 during in vivo ovarian follicle maturation and ovulation. Subsequent in vitro tests showed that external pH of 8.5 enhances hormonally induced maturation and ovulation relative to pH of 7.6. These observations suggest that attention should be paid to the pH of incubation media used in basic research and in biotechnological applications relying on in vitro maturation and ovulation in teleosts. Further, an understanding of the physiological significance of the enhancing effect of alkaline pH on maturation and ovulation will require determination of the intrafollicular pH around the oocyte during the periovulatory period.

Animals↗
PubMed2003

Factors affecting follicular populations on Day 3 postweaning and interval to ovulation in a commercial sow herd.

Sows (n=146) in a commercial herd were studied to determine factors affecting follicular populations and interval to ovulation after weaning. Ovaries were examined daily by ultrasonography beginning on Day 3 postweaning and twice daily from Day 4.5 until ovulation. Ovarian images were recorded on videotape on Day 3 postweaning and follicles were counted. Subsequent ultrasounds were used to determine time of ovulation. Sows with short weaning to ovulation intervals ( or=9 days) weaning to ovulation intervals (P<0.001). Follicular populations in sows with intermediate (7-8.5 days) intervals to ovulation were intermediate in diameter when compared to sows with short or long intervals to ovulation. Parity and body condition score (BCS) affected interval to ovulation; first parity and low body condition sows had longer intervals to ovulation (P<0.001 and 0.05, respectively). The longer intervals to ovulation in first parity and low body condition sows were associated with lesser follicular diameters on Day 3 after weaning. We conclude that follicular populations measured by ultrasonography on Day 3 after weaning were different for sows with different intervals to ovulation. Furthermore, production factors (i.e. parity and BCS) known to influence interval to ovulation were associated with differences in follicular growth within the first 3 days after weaning in sows.

Animals↗
PubMed2006

Relationship between the first ovulation within three weeks postpartum and subsequent ovarian cycles and fertility in high producing dairy cows.

The aim of this study was to investigate the relationship between the first ovulation within 3 weeks postpartum and subsequent ovarian cycles and fertility in high producing dairy cattle in Hokkaido, Japan. In Experiment 1, 110 cows (44 primiparous and 66 multiparous) were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent ovarian cycles. Milk samples were collected twice weekly from 7 to 100 days postpartum. The first ovulation was identified by an increase in milk progesterone (P4) to more than 1 ng/ml within 3 weeks postpartum. The numbers of cows showing ovulation and anovulation within 3 weeks postpartum were 31 (70.5%) and 13 (29.5%) in the primiparous cows and 35 (53.0%) and 31 (47.0%) in the multiparous cows, respectively. The patterns of ovarian resumption after calving were classified into two types (normal ovarian cycles and abnormal ovarian cycles) on the basis of milk P4 concentrations. Initiation of normal ovarian function in cows ovulated within 3 weeks postpartum occurred earlier than in anovulated cows regardless of the number of calvings (primiparous, 27.8 days vs. 44.4 days; multiparous, 30.6 days vs. 55.7 days; P<0.01). Out of the multiparous cows that ovulated within 3 weeks postpartum, initiation of normal ovarian function followed by a normal luteal phase was earlier than when it was followed by an abnormal luteal phase (25.5 days vs. 40.4 days; P<0.05). Milk P4 concentrations after the first ovulation were lower than those after the second ovulation in both the primiparous and multiparous cows (P<0.05). In Experiment 2, 22 multiparous cows were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent fertility. Blood samples were collected once a week from 0 to 3 weeks postpartum. The interval from parturition to first service in ovulated cows was shorter than in anovulated cows (68.4 days vs. 94.8 days; P<0.05). The conception rate by 100 days after calving tended to be higher in ovulated cows than in anovulated cows (50.0% vs. 16.7%, P=0.09). In conclusion, our data strongly suggests that ovulation within 3 weeks postpartum is a crucial phenomenon for subsequent resumption of ovarian function and conception, and thus it can be used as an index of subsequent reproductive performance.

Animals↗
PubMed1997

Preovulatory follicle development and ovulation in the brushtail possum (Trichosurus vulpecula) monitored by repeated laparoscopy.

The common method for synchronizing oestrus in brushtail possums is by removal of their pouch young (RPY). However, there is little information on the ovarian response to this treatment, the timing and incidence of ovulation is poorly defined, and methods of identifying oestrus are unreliable. In this study, the development of preovulatory follicles, ovulation and reproductive tract changes following RPY were monitored by repeated laparoscopic observation. A total of 120 adult female possums underwent laparoscopy at intervals of 1-4 days over the period from 0 to 21 days after RPY. Tissue was collected from a further 30 animals for correlative histology of ovarian structures, and to quantify changes in reproductive tract organs. Only 80 of 120 animals ovulated, and the time of ovulation ranged from 7 to 18 days following RPY. In most animals, enlargement of vaginal cul-de-sac and uterine tissue occurred within 10 days. Correlative histology supported the macroscopic classification of ovarian structures, and healthy and atretic follicles could be identified by laparoscopy. Vaginal smears and plasma progesterone concentrations verified the occurrence of ovulation as observed by laparoscopy. A 'presumptive' preovulatory follicle, first identifiable approximately 5 days before ovulation, was recorded in all animals that ovulated and in none that failed to ovulate. Changes to its surface morphology indicated impending ovulation. This study has enabled the day of ovulation to be identified accurately for the first time in this species. It has also shown that there is wide variation in follicle development, lack of synchrony in the time of ovulation in the brushtail possum, and that some animals fail to ovulate following RPY.

Animals↗
PubMed1992

[Double ovulation in mares. Clinical, hormone analytical and sonographic studies].

108 mares with a total of 135 oestrous cycles were examined. 30% of the mares showed development of double follicles, found by palpation and ultrasonography. Eight cases of double ovulation, four of them synchronous and four asynchronous, were examined closely. These cases of double ovulation showed different growth and different development of the follicular wall. This occurred at the same time in cases of synchronous double ovulation whereas it differed in case of asynchronous double ovulation. The later ovulating follicle was still growing while the first one had already burst. With both forms of double ovulation an equal concentration of progesterone was detected in peripheral blood. On the day of ovulation the rate of progesterone was low (1 ng/ml blood plasma) and it first started rising from the day +1 on. Double follicles matured slower than single follicles. Mares with synchronous double ovulation showed the typical oestrus behavior. This behavior was less distinct after the first ovulation in mares with asynchronous double ovulation. All four mares with asynchronous and two mares with synchronous double ovulation became pregnant. Twins did not occur. A possible relationship between double ovulation and twin pregnancy is discussed.

Animals↗
PubMed1983

The inter-ovarian distribution of twin ovulations and embryo survival in the bovine.

Data in the literature on twin ovulations and twin pregnancies were used to examine the distribution (unilateral vs bilateral) of twin ovulations and associated effects on embryo survival. Unilateral twin ovulations averaged 52% but there was significant heterogeneity among sources. Twenty-five percent of subjects which became pregnant following twin ovulations had unilateral twin ovulations. This suggests that fertilisation failure or embryo mortality, or both, are greater for unilateral twin ovulations. Using data on pregnant cows, the probability of embryo loss increased by an estimated 0.22 for unilateral twin ovulations compared with bilateral twin ovulations or single ovulations. Using the estimates obtained, the expected litter size was calculated for a range of ovulation rates with varying proportions of unilateral twin ovulations and different levels of embryo mortality. Litter size was not very sensitive to the distribution of twin ovulations.

Journal Article↗
PubMed1993

Incidence of delayed ovulation in Holstein heifers and its effects on fertility and early luteal function.

In the first of 3 experiments 134 first-service and 108 repeat-breeder Holstein heifers were palpated at 12-hour intervals starting 24 hours after insemination to compare the incidence of delayed ovulation in the 2 groups. Delayed ovulation was defined as failure to ovulate within the first 24 hours after insemination. Ovulation occurred within 24 hours post insemination in 92.1% of the animals and was delayed in 7.9% of the cases, with no differences between first-service and repeat-breeder heifers, indicating that the subfertility of the repeat-breeder animals was not due to delayed ovulation. The duration of the delay was at most 12 hours since all the animals had ovulated by 36 hours post insemination. Conception rate of the 19 animals with delayed ovulation (42.1%) was not different (P>0.05) from that of the 223 heifers that ovulated on time (44.8%). In a second experiment, no differences were detected between 15 heifers with delayed ovulation and 15 animals that ovulated on time with respect to their progesterone concentrations during the first 8 days post insemination, indicating that delayed ovulation is not associated with delayed luteinization or subnormal early luteal function. In the third experiment, the conception rate of 126 repeat-breeder heifers that were treated with hCG at the time of insemination was 26.7%; the conception rate of 101 repeat-breeder heifers that were inseminated twice, at 12 and 24 hours after the onset of estrus, was 34.6%; and the conception rate of 105 repeat-breeder heifers which were not treated with hCG and which were inseminated only once was 30.5% (P>0.05) It is concluded that delayed ovulation is not an important cause of infertility and does not constitute an important component of the repeat-breeding syndrome in Holstein heifers.

Journal Article↗
PubMed1994

Effect of time of insemination relative to ovulation on fertility with liquid and frozen boar semen.

Precise data on fertility results following peri- and postovulatory insemination in spontaneously ovulating gilts is lacking. Using transcutaneous sonography every 4 h during estrus as a tool for diagnosis of ovulation, the effects of different time intervals of insemination relative to ovulation were investigated with liquid semen (Experiment 1, n=76 gilts) and frozen semen (Experiment 2, n=80 gilts). In Experiment 3 (n=24 gilts) the number of Day-28 embryos related to the various intervals between insemination and ovulation was determined after the use of liquid semen. Using liquid semen the fertilization rates based on Day-2 to Day-5 embryos and the number of accessory spermatozoa decreased significantly in gilts inseminated with 2 x 10(9) spermatozoa per dosage in intervals of more than 12 h before or more than 4 h after ovulation. In the time interval 4 to 0 h before ovulation, comparable fertilization rates were obtained using frozen semen (88.1%) and liquid semen (92.5%). Fertilization rates and numbers of accessory spermatozoa decreased significantly when gilts were inseminated with frozen semen more than 4 h before or 0 to 4 h after the detection of ovulation. The percentage of Day-28 embryos was significantly higher following preovulatory insemination compared to inseminations 0 to 4 h and 4 to 8 h after ovulation. It is concluded that the optimal time of insemination using liquid semen is 12 to 0 h before ovulation, and 4 to 0 h before ovulation using frozen semen. The results stress the importance of further research on sperm transport and ovulation stimulating mechanisms, as well as studies on the time of ovulation relative to estrus-weaning intervals and estrus duration.

Journal Article↗
PubMed1996

Ovule development: identification of stage-specific and tissue-specific cDNAs.

A differential screening approach was used to identify seven ovule-specific cDNAs representing genes that are expressed in a stage-specific manner during ovule development. The Phalaenopsis orchid takes 80 days to complete the sequence of ovule developmental events, making it a good system to isolate stage-specific ovule genes. We constructed cDNA libraries from orchid ovule tissue during archesporial cell differentiation, megasporocyte formation, and the transition to meiosis, as well as during the final mitotic divisions of female gametophyte development. RNA gel blot hybridization analysis revealed that four clones were stage specific and expressed solely in ovule tissue, whereas one clone was specific to pollen tubes. Two other clones were not ovule specific. Sequence analysis and in situ hybridization revealed the identities and domain of expression of several of the cDNAs. O39 encodes a putative homeobox transcription factor that is expressed early in the differentiation of the ovule primordium; O40 encodes a cytochrome P450 monooxygenase (CYP78A2) that is pollen tube specific. O108 encodes a protein of unknown function that is expressed exclusively in the outer layer of the outer integument and in the female gametophyte of mature ovules. O126 encodes a glycine-rich protein that is expressed in mature ovules, and O141 encodes a cysteine proteinase that is expressed in the outer integument of ovules during seed formation. Sequences homologous to these ovule clones can now be isolated from other organisms, and this should facilitate their functional characterization.

Amino Acid Sequence↗
PubMed2005

Maintenance of ovulation inhibition with the 75-microg desogestrel-only contraceptive pill (Cerazette) after scheduled 12-h delays in tablet intake.

BACKGROUND: In contrast to traditional progestagen-only pills (POPs), the desogestrel-only pill Cerazette consistently inhibits ovulation. This study was performed to test the hypothesis that desogestrel alone will keep inhibiting ovulation even when pills are taken 12 h late, indicating that delays in tablet intake of up to 12 h do not jeopardize contraceptive efficacy. METHODS: Women aged between 19 and 40 years with confirmed ovulation were admitted to this open-label pharmacodynamic study. They were treated with Cerazette for 56 days with three tablets to be taken 12 h late, having been randomized to a regimen with scheduled late tablets on Days 39, 42 and 49 (Group A) or on Days 11, 14 and 21 (Group B). The occurrence of ovulation during treatment was determined by measuring progesterone serum levels every 2 days. RESULTS: One of the 103 treated subjects ovulated during treatment. The ovulation incidence thus amounts to 1.0% (two-sided 95% confidence interval 0.02-5.29%). There was no apparent relationship between these ovulations and scheduled late tablets. The minimum time to first posttreatment ovulation was 7 days, whereas it took 17.2 days on average from last tablet intake until ovulation. CONCLUSIONS: Ovulation inhibition with Cerazette is maintained after 12-h delays in tablet intake and return of ovulation takes at least 7 days. These properties distinguish Cerazette from all other POPs.

Adolescent↗
PubMedDate not supplied

Impaired ovulation by 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) in immature rats treated with equine chorionic gonadotropin.

Several studies have established that 2,3,7,8 tetrachloro-p-dioxin (TCDD) blocks ovulation. The main purpose of this study was to determine if induced ovulation was delayed temporarily by TCDD. The ovulation model used was that of the gonadotropin-primed intact or hypophysectomized rat. Immature intact female Sprague-Dawley rats (IIR) were given 32 microg TCDD/kg by gavage on day 24 of age. The next day equine chorionic gonadotropin (eCG) (5 IU) was injected sc to stimulate follicular development. The number of ova in the oviducts, the ovulation rate, and steroid concentrations were determined at 72, 96, 120, and 144 h after eCG. Immature female Sprague-Dawley rats (IHR) were hypophysectomized on day 23 of age. On day 26, the IHR were given 20 microg TCDD/kg by gavage. The next day eCG (10 IU) was injected sc to stimulate follicle development and at 52 h after eCG, 10 IU human chorionic gonadotropin (hCG) was given to induce ovulation. The same parameters as in IIR were determined in IHR at 72, 96, and 120 h after eCG. TCDD decreased body and ovarian weight gains in both IIR and IHR. In IIR, TCDD delayed ovulation by 24 to 48 h reducing the number of ova shed as well as the number of animals ovulating at 72 and 96 h after eCG. In IHR, however, TCDD reduced only the number of ova shed but caused no delay in ovulation. The IIR treated with TCDD had low levels of progesterone (P4) at 72 and 96 h after eCG but high levels of estradiol (E2) at the same time points. This sustained high level of E2 production coincided with a transient decrease in serum concentrations of androstenedione (A4). The alteration of steroid hormones by TCDD was restored to normal by 48 h after ovulation in IIR. Serum P4 concentration was not altered by TCDD in IHR at 72 h after eCG but was decreased thereafter. The delay in ovulation induced by TCDD in IIR indicates the disruption of the hypothalamus-pituitary-ovary axis during proestrus. The decrease in number of ova shed in IHR induced by exogenous gonadotropins indicates an additional direct ovarian effect of TCDD in blocking ovulation.

Administration, Oral↗
PubMed1980

Progesterone levels after induction of ovulation in dioestrous rats.

Maximal levels of progesterone in the plasma after premature ovulation induced by either the administration of human chorionic gonadotrophin (HCG) or LH-releasing hormone (LH-RH) to dioestrous (day 0) rats were observed from 33 to 45 h/but/decreased/3 h earlier than after spontaneous ovulation. This suggested an earlier decline in the secretory activity of corpora lutea formed from premature ovulations than that of corpora lutea formed during a normal oestrous cycle. The next spontaneous ovulation occurred 4 days (day 5) after premature ovulation induced by LH-RH on day 0. A single s.c. injection of 2.5 microgram oestradiol-17 beta (OE2) at 10.00 h on day 2 to these animals advanced the next spontaneous ovulation by 1 day. A normal number of oocytes was shed, indicating that earlier secretion of oestrogen on day 2 had advanced the next spontaneous ovulation. A single injection of 2.5 microgram OE2 to normal 4-day cyclic rats at metoestrus failed to advance the next ovulation. An earlier decline of progesterone levels in the plasma of rats after premature ovulation as compared with spontaneous ovulation may explain the greater effectiveness of oestrogen in the former group. The progesterone surge was observed during the period of premature ovulation in both HCG- and LH-RH-treated groups. This progesterone release in the periovulatory period may be responsible for the inhibition of gonadotrophin surges on the expected day of proestrus (day 1).

Animals↗