Search Results

Summary. Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17β (15 mg) and progesterone (37·5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2·0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development.

In Exp. 1, 22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2α and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2α injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 ± 4 days (static phase). Then follicles developed which ovulated within 3–7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (± s.e.m.) concentrations of LH, FSH, oestradiol-17β and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P < 0·1) in cows with cysts (2·9 ± 0·2) than in cows without cysts (1·1 ± 0·1) or control cows (1·4 ± 0·2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P < 0·1) in cows with cysts (3·6 ± 0·3 and 2·2 ± 0·3, respectively) than in non-cystic (2·3 ± 0·2 and 1·0 ± 0·2, respectively) and control (1·8 ± 0·1 and 1·1 ± 0·2, respectively) groups during the follicular phase.

In Exp. 2, 20 non-lactating, non-pregnant dairy cows were used: 15 cows received exogenous steroids as previously described. Hypothalamic and hypophysial tissues were collected after diagnosis of cystic structures in 11 cows (cystic group). The remaining 4 cows in the steroid-treated group ovulated and were assigned to the control group in addition to 5 non-steroid treated cows. Hypothalamic and hypophysial tissues were collected during the late-luteal phase (Days 16–18) from these control cows (N = 9). Anterior pituitary concentrations (μg/g) of LH (60·5 ± 11·0, 44·6 ± 11·7), FSH (30·2 ± 4·0, 22·1 ± 4·6) and receptors for GnRH (17·2 ± 2·2, 23·4 ± 2·6 m × 10⁻¹⁰/mg protein) did not differ between cows with cysts and control cows, respectively. Content of GnRH (ng) in the combined preoptic area and hypothalamus proper was higher (P < 0·05) in control cows (37·7 ± 6·6) than cows with cysts (18·6 ± 6·1). In the pituitary stalk median eminence, GnRH content (ng) tended to be higher (P ≥ 0·1) in cows with cysts (38·5 ± 9·6) compared with control (21·1 ± 15·2) cows.

Secretory patterns (mean concentration, pulse frequency and amplitude) of LH were therefore increased during the follicular phase in cows which developed cysts compared to cows which subsequently ovulated. In addition, hypothalamic GnRH content, but not pituitary characteristics, appeared to be altered in cows with cysts.

Keywords: ovary; follicular cysts; dairy cattle; gonadotrophins; hypothalamus; pituitary

Polycystic ovary syndrome (PCOS) is the most prevalent endocrine pathology among women in reproductive age. Its main symptoms are oligo or amenorrhea, hyperandrogenism and the presence of ovarian cysts. It is also associated with infertility, obesity and insulin resistance. Mainly due to its heterogeneity, PCOS treatments are directed to manage its symptoms and to prevent associated diseases. The correct formation and regression of blood vessels during each ovarian cycle is indispensable for proper follicular development, ovulation and corpus luteum formation. The importance of these processes opened a new and promising field: ovarian angiogenesis. Vascular alterations characterize numerous pathologies, either with increased, decreased or abnormal angiogenesis. In the last years, several anomalies of ovarian angiogenesis have been described in women with PCOS. Therefore, it has been suggested that these alterations may be associated with the decreased – or lack of – ovulation rates and for the formation of cysts in the PCOS ovaries. Restoration of a proper vessel formation in the ovaries may lead to improved follicular development and ovulation in these patients. In the present review, we attempt to summarize the alterations in ovarian angiogenesis that have been described in women with PCOS. We also discuss the therapeutic approaches aimed to correct these alterations and their beneficial effects on the treatment of infertility in PCOS.

The hypothesis that pregnancy success could be improved in early postpartum ewes by prolonging the lifespan of the corpus luteum via active immunization against prostaglandin F_2α (PGF_2α) was tested. Further experiments in ewes immunized against PGF_2α investigated the effects of exogenous PGF_2α on the preovulatory follicle and the effects of PGF_2α and oestradiol benzoate on corpus luteum function. Four weeks prepartum, 39 ewes bred to lamb during seasonal anoestrus received either 5 mg PGF_2α–ovalbumin conjugate (n = 20; immunized) or ovalbumin (n = 19; control) in Freund's complete adjuvant. Treatments were repeated on day 5 post partum with reagents emulsified in Freund's incomplete adjuvant. On day 17 post partum, ewes received 500 iu pregnant mares' serum gonadotrophin (PMSG) and 48 h later 50 μg gonadotrophin-releasing hormone (GnRH). Laparoscopy was performed 36 h after GnRH to assess ovarian activity and ewes with recent ovulations were inseminated into the uterus. No immunized ewes had ovulated, but ten had follicles that luteinized and secreted progesterone during the 8 weeks studied. Eighteen of 19 control ewes ovulated and 15 of 18 had increased progesterone concentration for at least 21 days. By day 70 post partum, progesterone had returned to basal values in all control ewes. In a second study, 24 immunized ewes bearing persistent corpora lutea, and for which the interval from the previous parturition was greater than 90 days, received 15 mg PGF_2α and 500 iu PMSG followed 48 h later by 50 μg GnRH. PGF_2α induced corpus luteum regression in all ewes. PMSG and GnRH treatments resulted in oestrus in 21 of 24 ewes. Sixteen hours after GnRH, 10 ewes received a second injection of 15 mg PGF_2α. PGF_2α induced follicular rupture in eight of ten immunized ewes, whereas only two of 14 ewes not receiving PGF_2α ovulated (P < 0.01). All anovular ewes had large cystic follicles that luteinized. In a third study, 22 ewes immunized against PGF_2α, and having persistent corpora lutea, received, on two consecutive days, either oestradiol benzoate (750 μg; n = 11) in oil or oil (n = 11). Laparoscopy was performed on all ewes immediately before injections and four of the 11 ewes in each group possessed uterine horns that were filled with fluid. No fluid was judged to be in the horns of the remaining seven ewes in each group. On the basis of serum concentrations of progesterone and laparoscopies, oestradiol benzoate induced luteal regression in those ewes with uterine fluid and failed to induce luteal regression in those ewes lacking uterine fluid. Luteal function was unaffected in ewes that received the oil vehicle. These data suggest that premature luteal regression was not the reason for failure of occurrence of pregnancy. Immunization against PGF_2α was effective in blocking ovulation, but not in inhibiting oestrous behaviour or the formation of persistent luteal tissue. Treatment of immunized ewes with exogenous PGF_2α restored the ability of ewes to ovulate, providing further evidence for the involvement of PGF_2α in ovulation. The ability of oestradiol to induce luteolysis in immunized ewes was associated with the presence of uterine fluid.

Endocrine-disrupting chemicals (EDCs) are exogenous agents with the ability to interfere with processes regulated by endogenous hormones. One such process is female reproductive function. The major reproductive organ in the female is the ovary. Disruptions in ovarian processes by EDCs can lead to adverse outcomes such as anovulation, infertility, estrogen deficiency, and premature ovarian failure among others. This review summarizes the effects of EDCs on ovarian function by describing how they interfere with hormone signaling via two mechanisms: altering the availability of ovarian hormones, and altering binding and activity of the hormone at the receptor level. Among the chemicals covered are pesticides (e.g. dichlorodiphenyltrichloroethane and methoxychlor), plasticizers (e.g. bisphenol A and phthalates), dioxins, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons (e.g. benzo[a]pyrene).

Summary. Anoestrous Romney Marsh ewes with (+P) and without (−P) progesterone pretreatment were induced to ovulate by multiple low-dose injection of GnRH followed by a bolus injection of GnRH. Luteal function was assessed by twice daily measurement of plasma progesterone. Animals were slaughtered on Days 3 or 5 after the end of GnRH treatment and CL and endometrium were recovered. In all Day-5 ewes, blood samples were collected at 30-min intervals for 8 h on Days 3 and 5 for measurement of PGFM and oxytocin. At slaughter 92% of the Group +P ewes had ovulated compared with 54% of the Group −P ewes. The ovaries of some of the Group −P ewes only contained luteinized cysts either alone or in association with CL. In the ewes that ovulated, progesterone profiles were normal in all Group +P ewes, whereas Group −P ewes had 'normal' or 'abnormal' profiles in which plasma progesterone was declining prematurely. All of the CL from ewes with abnormal progesterone profiles were associated with follicular cysts, and were significantly smaller and with a lower progesterone content on Day 5. PGFM levels decreased (P < 0·05) between Days 3 and 5 in ewes in Groups +P and −P with 'normal' CL but increased (P < 0·01) in Group −P ewes with 'abnormal' CL. Oxytocin levels were lower in Group −P ewes with 'abnormal' CL on Day 5, than in 'normal' ewes in Groups −P (P < 0·01) or +P (P < 0·05). In 3/5 Day-5 ewes with 'abnormal' CL there was a clear association between a major peak of oxytocin and a rise in PGFM during the frequent sampling period on Day 3 or Day 5, and endometrial oxytocin binding sites were present at slaughter. This suggests that the premature regression of 'abnormal' CL occurs via the normal luteolytic mechanism. Although ewes in Groups +P and –P with 'normal' CL had similar progesterone profiles, plasma oxytocin was significantly higher (P < 0·05) in the Group −P ewes and oxytocin binding sites were present only in this group, suggesting that progesterone pretreatment can influence the production of both oxytocin and its receptor.

Keywords: abnormal corpus luteum; oxytocin; prostaglandin F-2α; ewe; luteolysis

Premature ovarian insufficiency (POI) occurs in 1% of reproductive-age women. The ovarian manifestation ranges from the presence of a variable population of follicles (follicular) to the absence of follicles (afollicular), and in the majority of cases the cause is unknown. A transgenic mouse model of follicular POI, the Double Mutant (DM), arises from oocyte-specific deletion of Mgat1 and C1galt1 required for the generation of O- and N-glycans. DM females are subfertile at 6 weeks, infertile by 9 weeks and exhibit POI by 12 weeks of age. In this study we investigate the cause of the reduced fertility at 6 weeks and infertility at 9 weeks of DM females. Ovary sections were used to analyse follicle and corpora lutea (CL) numbers, apoptosis, and levels of laminin and 3β-hydroxysteroid dehydrogenase using immunohistochemistry. After POI, DM females unexpectedly remained sexually receptive. At both 6 and 9 weeks, DM ovaries contained more primary follicles, however, at 9 weeks DM follicles were proportionally healthier, revealed by TUNEL analysis compared with Controls. In 9 week DM ovaries (collected post-mating), secondary follicles had theca and basal lamina structure abnormalities, whilst preovulatory follicles failed to ovulate resulting in the presence of numerous luteinised unruptured follicles, indicative of ovulation failure. Finally, DM ovaries contained more regressing CL with decreased luteal cell apoptosis indicative of a defect in CL regression. Identifying these follicular modifications have provided insight into the aetiology of a model of POI and highlight targets to investigate with the hope of developing new fertility treatments.

Summary. The secretion rates of testosterone measured during the last half of the oestrous cycle in 2 Merino crossbred ewes with utero-ovarian autotransplants were 1·95 ± 0·34 ng/min and 2-48 0-63 ng/min. The secretion rate of testosterone was not correlated with the secretion rate of oestradiol or androstenedione in either ewe.

Welsh Mountain ewes were actively immunized against testosterone-3-(0carboxymethyl)-oxime-bovine serum albumin (testosterone-3-BSA) or BSA alone (controls). Immunization against testosterone-3-BSA (5 ewes) resulted in anovulation (2 ewes) and the disruption of oestrous cycles and irregular ovulations (2 ewes). The ovaries showed morphological and endocrinological evidence of over-stimulation. Numerous large non-atretic follicles were present and in those ewes still ovulating the numbers of corpora lutea (ovulation rate) were increased. The concentrations of androstenedione and of oestradiol in the ovarian venous plasma were also markedly increased when compared to those in control ewes. The plasma binding capacity for steroids and the jugular venous concentrations of steroids were higher in immunized ewes. The binding capacity of follicular fluid for testosterone was similar to that of jugular venous plasma from the same ewe.

These results show that immunization against testosterone-3-BSA leads to a disruption of ovarian cycles and ovarian over-stimulation.

Summary. In a series of 5 experiments, ewes were treated with implants releasing oestradiol-17β and the effects on ovulation rate were observed. Large doses of oestradiol-17β (> 20 μg/day) produced anovulation while smaller amounts only reduced the proportion of twin ovulations. Amounts of exogenous oestradiol comparable to ovarian production rate in the luteal phase (< 1 μg/day) produced a significant (P < 0·01) suppression in ovulation rate. Treatment during the follicular phase of the oestrous cycle was most effective, but treatment during the luteal phase alone also appeared to suppress ovulation rate. Furthermore, in 2 of 3 experiments ewes treated with low amounts of oestradiol during the first half of the luteal phase were less likely to have multiple ovulations at the subsequent oestrous period. The results support the hypothesis that oestrogen is involved in the physiological control of ovulation rate in the ewe, but this action is probably not restricted to the assertion of dominance by a maturing follicle during the follicular phase.

Keywords: oestrogen; ovulation rate; sheep

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in non-reproductive females is thought to play an important role in maintaining reproductive skew. Pituitary sensitivity and ovarian structure were examined in three groups of females that differed with respect to their social environment and breeding status to determine whether anovulation is due to inhibitory social cues or is merely the result of a lack of copulatory stimulation. The contribution of gonadal steroid negative feedback to neuroendocrine differences in the reproductive systems of the respective groups was also investigated. LH secretion after a 0.5 micrograms GnRH challenge in females that had been removed from the presence of the breeding individuals for at least 6 months (removed non-reproductive females) was significantly higher than in non-reproductive females in the colony, but significantly lower than in reproductive females. In both removed non-reproductive females and reproductive females, corpora lutea were observed in ovaries of seven of eight females, indicating that ovulation occurs spontaneously in subordinate females on removal from the breeding pair. Circulating progesterone concentrations in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hystero-ovariectomy, reproductive females continued to show significantly greater GnRH-stimulated LH secretion than non-reproductive females. Thus, differential inhibition of gonadotrophin secretion in breeding and non-breeding females occurs independently of gonadal steroids. It is concluded that female Damaraland mole-rats are spontaneous ovulators and that anovulation results from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of the hypothalamo-pituitary-gonadal axis has the potential to play a causal role in maintaining reproductive skew in colonies of C. damarensis.

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in non-reproductive females is thought to play an important role in maintaining reproductive skew. Pituitary sensitivity and ovarian structure were examined in three groups of females that differed with respect to their social environment and breeding status to determine whether anovulation is due to inhibitory social cues or is merely the result of a lack of copulatory stimulation. The contribution of gonadal steroid negative feedback to neuroendocrine differences in the reproductive systems of the respective groups was also investigated. LH secretion after a 0.5 micrograms GnRH challenge in females that had been removed from the presence of the breeding individuals for at least 6 months (removed non-reproductive females) was significantly higher than in non-reproductive females in the colony, but significantly lower than in reproductive females. In both removed non-reproductive females and reproductive females, corpora lutea were observed in ovaries of seven of eight females, indicating that ovulation occurs spontaneously in subordinate females on removal from the breeding pair. Circulating progesterone concentrations in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hystero-ovariectomy, reproductive females continued to show significantly greater GnRH-stimulated LH secretion than non-reproductive females. Thus, differential inhibition of gonadotrophin secretion in breeding and non-breeding females occurs independently of gonadal steroids. It is concluded that female Damaraland mole-rats are spontaneous ovulators and that anovulation results from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of the hypothalamo-pituitary-gonadal axis has the potential to play a causal role in maintaining reproductive skew in colonies of C. damarensis.