Luteal-follicular Transition Research Articles

P-359 Effect of estradiol pretreatment on antagonist ICSI cycles outcome

Abstract Study question Does estrogen pretreatment in antagonist ICSI cycles improves the outcome? Summary answer Pretreatment with estrogen in antagonist cycles reduced the days of stimulation, the number of hMG ampoules and enhanced the implantation rate. What is known already It has been previously reported that, programming of antagonist cycles with E2 only, started in the luteal phase and continued beyond the menses till the first day of stimulation, yielded similar results as the long agonist protocol. E2 pre-treatment in the luteal phase has an inhibiting role on follicular growth through its negative feedback on the FSH increase during the luteal follicular transition phase. This effect stops as soon as E2 administration is terminated. Study design, size, duration This was a prospective randomized controlled trial performed in a private IVF centers from June 2020 to February 2021. One hundred and fourteen infertile couples undergoing intracytoplasmic sperm injection embryo transfer cycles (ICSI-ET) were included. Participants/materials, setting, methods Group A includes 57 patients were pretreated with a dose of 4 mg estradiol valerate (progynova 2 mg; Bayer) once daily starting 10days before expected menses. Ovarian stimulation was started one day after the last estradiol dose, in a dose ranging from 225 to 375 IU of hMG. While in group B , 57 patients received stimulation in a dose of 225 to 375 IU of hMG starting on cycle day 2 without estradiol pretreatment. Main results and the role of chance The daily dose of hMG was significantly lower in The study group (P = 0.048), the stimulation days were significantly higher in the control group (P = 0.049), the total number of hMG ampoules was significantly higher in the control group (P = 0.041), and the implantation rate was higher in the study group (P = 0.045) , also the pregnancy rate (positive pregnancy test) was higher in the study group (p = 0.044) but there was no significant statistical difference detected as regards the clinical pregnancy rate between both groups (P = 0.180) , the serum estradiol on day of hCG ( p = 0.055), serum progesterone level on hCG day (P = 0.71) and the endometrial thickness (p = 0.780) . Also there is no significant statistical difference between the two groups as regarding number of follicles on day of hCG. (P = 0.803), the number of mature oocytes (P = 0.703) and no significant difference in the number of good quality embryos (p = 0.532) and the ratio of mature oocytes to number of follicles on day of hCG (P = 0.835), with no significant statistical difference between both groups. Limitations, reasons for caution The limitation of this study is the small number of patients as we included only 114 patients. Wider implications of the findings Luteal estradiol in antagonist cycles improved the outcomes of ICSI procedure by reducing the number of gonadotropin ampoules used for COH and reduced duration of stimulation, also the implantation rate is improved by luteal estradiol administration. Trial registration number NCT05197374

Hormonal Profiles of Menstrual Bleeding Patterns During the Luteal-Follicular Transition.

Menstrual cycle function is determined by a complex endocrine axis that controls the ovaries and endometrium. While the late luteal phase is characterized by declining progesterone and estrogen, how these hormonal profiles relate to menstrual bleeding patterns is not well understood. Characterize associations between luteal phase hormonal profiles and subsequent menstrual bleeding patterns, specifically spotting before bleeding. We examined creatinine-adjusted urinary estrone 3-glucuronide (E13G) and pregnanediol 3-glucuronide (Pd3G) levels in relation to spotting in 116 premenopausal women (ages 20-47) who kept daily menstrual diaries and collected first morning urine samples for ≥ 2 consecutive cycles or 1 luteal-follicular transition (n = 283 transitions). We used linear mixed models to estimate associations between luteal phase hormone levels and spotting before bleeding. Transitions with ≥ 1 days of spotting before menstrual bleeding (n = 118) had greater luteal phase Pd3G levels vs nonspotting transitions (n = 165). Differences in Pd3G between spotting and nonspotting transitions were largest at menses onset (34.8%, 95% confidence interval, 18.9%, 52.7%). Pd3G levels for spotting transitions dropped to similar levels as nonspotting transitions an average of 1 day later, which aligned with the first day of bleeding for transitions with contiguous spotting. Spotting transitions were preceded by slower rates of Pd3G decline than nonspotting transitions, whereas E13G declines were similar. Self-reported bleeding patterns may provide insight into luteal phase Pd3G levels. First bleed appears to be the best choice for defining the end of the luteal phase and achieving hormonal consistency across transitions.

Sequential (hFSH + recFSH) vs homogenous (hFSH or recFSH alone) stimulation: clinical and biochemical (cumulus cell gene expression) aspects

FSH is a key hormone in the regulation of follicular development. Together with the EGF network, these molecules mediate oocyte maturation and competence in preparation for the action of LH. FSH isoforms regulate distinct biological pathways and have specific effects on granulosa cell function and maturation of the ovarian follicle. Their dynamic interactions occur during the follicular cycle; short-living forms are predominant in the pre-ovulatory phase, whereas long-acting molecules characterize the luteal-follicular transition. Recombinant FSH (rFSH) molecules have a reduced number of isoforms and are less acidic, with a shorter half-life. We have investigated sequential stimulation, comparing hFSH + rFSH, vs. rFSH alone and hFSH alone for the entire stimulation phase. Sequential stimulation leads to an E2 per MII oocyte ratio that is much lower than is seen during treatment with the two drugs individually. Although there is a positive tendency in favor of the sequential treatment, there was no significant difference in pregnancy rates, even taking frozen embryos into consideration. The cumulus cell transcriptome varies considerably between the treatments, although with no clear significance. When comparing pregnant vs. non-pregnant patients, in general a decrease in mRNA expression can be observed in the pregnant patients, especially in expression of folic acid receptor 1 and ovostatin 2. This indicates that material has been transferred from CC to the oocyte. However, a common observation in the literature is that variations in the transcriptome of the cumulus cells are highly dependent upon the patient genotype; the potential for applying this strategy as a basis for selecting embryos is, at the very least, questionable.

The normal menstrual cycle in women

The menstrual cycle in women is characterised by high variability in cycle length (26–35 days), 5-day menses, a fertile phase from 5 days before to the day of ovulation, and low fertility which is dependent on cycle length and age. All women show an FSH rise at the luteal–follicular transition, stimulating a cohort of follicular growth and inhibin B secretion in the early follicular phase. The ovulatory dominant follicle (DF) is selected in the mid-follicular phase, and as this DF grows it increasingly secretes oestradiol and inhibin A for a week before ovulation. Gonadotrophin responsiveness, IGF binding protein expression and degradation, and vascularisation have been identified to be crucial for DF selection and progression. Two-thirds of women show two follicle waves and 1/3 show 3 follicle waves per cycle. Three-wave women have longer cycles, and a later oestradiol rise and LH surge. The corpus luteum secretes progesterone, oestradiol and inhibin A in response to LH pulses, and reaches its peak in terms of size, secretions, and vascularization 6–7 days after ovulation. Luteal regression is passive and independent of the uterus, but can be prevented by hCG, the luteotrophic signal from the trophoblast, from 8 days after conception. Reductions in systemic steroid and protein hormone concentrations may be responsible for the FSH rise characteristic of premenopausal women. The functional layer of the endometrium shows steroid hormone-dependent proliferation, differentiation, and shedding in the absence of the trophoblast. Menstruation is initiated by progesterone responsive decidual cells, and executed by PGE and PGF2α, vasoconstriction and matrix metalloprotease secretion by leukocytes. Ovarian function and also hormone fluctuations during the menstrual cycle are similar to oestrous cycles of cows and mares, justifying research into comparative aspects of menstrual and oestrous cycles in monovulatory species.

Luteal phase estradiol versus luteal phase estradiol and antagonist protocol for controlled ovarian stimulation before in vitro fertilization in poor responders

Luteal phase synchronization of follicular growth has been suggested as a means to improve ovarian response in low responders. We compared luteal E2 and antagonist (n=256) with luteal E2 only (n=57) before antagonist protocol in low responders. The addition of GnRH antagonist to luteal E2 for luteal suppression before ovarian stimulation for IVF does not improve IVF outcomes in poor responders.

Mechanisms of FSH synthesis: what we know, what we don't, and why you should care

The pituitary gonadotropin hormones, FSH and LH, are key regulators of reproductive physiology. Though the two hormones are produced by the same cell type, often in response to the same endocrine and paracrine regulators, they sub-serve different biological functions and their synthesis and secretion are differentially regulated. This stems largely from differences in transcriptional, post-transcriptional, and post-translational regulation of their unique beta subunits. That is, both hormones are dimeric glycoproteins and share a common alpha subunit. Their unique beta subunits, however, derive from different genes encoding distinct proteins. Past and recent research indicates synthesis and release of the two hormones are subject to extensive and independent regulation. LH appears to be secreted predominantly via the regulated secretory pathway, whereas FSH release is largely constitutive. As such, investigations of FSH-beta subunit synthesis may lend direct insight into mechanisms underlying patterns of secreted FSH, more so than investigations of the LHbeta subunit. Here, we review recent investigations of transcriptional regulation of the FSH-beta subunit gene from different mammalian species, including humans. The results reveal both conserved and species-specific regulatory mechanisms that might contribute to inter-species variation in FSH release.

Early follicle development during the luteal-follicular transition affects the predictability of serum follicle-stimulating hormone but not antimüllerian hormone levels on cycle day 3

To verify whether the presence of an overdeveloped antral follicle modifies the expected relationship between serum antimüllerian hormone (AMH), estradiol, or follicle-stimulating hormone (FSH) levels and antral follicle count on cycle day 3. Prospective study. Teaching hospital, France. Two hundred seventy-seven normo-ovulating women. Serum AMH, estradiol, and FSH levels and the number and size of antral follicles (3 to 12 mm) were measured on cycle day 3. Two groups were set according to the presence ("large" group) or absence ("small" group) of at least one follicle measuring >7 mm. Hormonal-follicular correlation. Whereas, as expected, the correlation between FSH and follicle counts was affected by the presence of an overdeveloped follicle, the correlation between AMH and follicle counts remained unaffected. Estradiol failed to be correlated with antral follicle counts in both groups. In contrast with FSH, AMH levels remain tightly correlated to the number of antral follicles despite the presence of early growing follicles on cycle day 3.

Early follicle development alters the relationship between antral follicle counts and inhibin B and follicle-stimulating hormone levels on cycle day 3

To verify whether, during the luteal-follicular transition, increased inhibin B production by abnormally large follicles modifies the expected relationship between the number of follicles and peripheral inhibin B and FSH levels. Prospective study. Teaching hospital, France. A total of 192 normo-ovulatory women. Serum inhibin B and FSH levels and numbers and sizes of antral follicles (3-12 mm) were measured on cycle day 3. The strength of hormonal-follicular correlations was assessed in two groups formed according to the presence (large follicle group; n = 73) or absence (small follicle group; n = 119) of one follicle measuring >7 mm. Serum inhibin B and FSH levels were correlated with antral follicle counts (r = 0.32 and r = -0.44, respectively). These relationships were significantly weaker in the large follicle group (r = 0.24 and r = -0.28, respectively) than in the small follicle group (r = 0.51 and r = -0.55, respectively). Antral follicle size influences serum inhibin B and FSH levels and alters their expected relationship with the number of antral follicles on day 3. These results contribute to clarifying the controversial role of serum inhibin B and FSH levels in the prediction of ovarian follicular status.

Activator Protein-1 and Smad Proteins Synergistically Regulate Human Follicle-Stimulating Hormone β-Promoter Activity

GnRH1 stimulates the synthesis and secretion of FSH and LH from the anterior pituitary gland. The molecular mechanisms through which GnRH1 produces these effects in humans have not been determined. Here, we examined transcriptional regulation of the human FSHbeta (FSHB) subunit using reporter assays in immortalized murine gonadotrope cells. GnRH1 dose and time dependently stimulated FSHB promoter activity, with peak stimulation occurring at 8 h. GnRH1 rapidly stimulated various MAPK cascades, though the ERK1/2 and p38 pathways appeared to be most critical for FSHB induction. Indeed, constitutively active forms of both Raf1 kinase and MAP2K6 (MKK6) were sufficient to stimulate reporter activity. GnRH1 stimulated activator protein-1 (AP-1) (FosB, c-fos, JunB, and cJun) synthesis and complex formation, the latter of which bound to a conserved cis-element within -120 bp of the transcription start site. A second, lower affinity, site was mapped more proximally. Mutations of both cis-elements diminished GnRH1-stimulated promoter activity, though disruption of the higher affinity site had a more dramatic effect. A dominant-negative Fos protein dose dependently inhibited GnRH1-stimulated FSHB transcription, confirming a role for endogenous AP-1 proteins. MAPK kinase 1 (MEK1) and p38 inhibitors significantly attenuated GnRH1-stimulated c-fos, FosB, and JunB synthesis, suggesting a mechanism whereby the ERK1/2 and p38 signaling pathways regulate FSHB transcription. Activins and inhibins potently regulate FSH synthesis in rodents, but their roles in FSH regulation in humans are less clear. Activin A, though weak on its own, synergized with GnRH1 to stimulate human FSHB promoter activity. In contrast, activin A partially inhibited GnRH1-stimulated LHbeta subunit (LHB) transcription. The GnRH1 and activin A signaling pathways appear to converge at the level of the high-affinity AP-1 site. Fos and Jun proteins synergistically regulate reporter activity through this element, and their effects are potentiated by coexpression of either Smad2 or Smad3, effectors in the activin signaling cascade. In summary, GnRH1 and activin A synergistically regulate human FSHB subunit transcription. The combined actions of AP-1 and Smad proteins acting through a conserved AP-1 element provide a candidate mechanism for this effect. The ability of activins to potentiate selectively the effects of GnRH1 on FSHB expression suggests a model for preferential increases in FSH secretion at the luteal-follicular transition of the menstrual cycle.

Luteal phase estrogen is decreased in regularly menstruating older women compared with a reference population of younger women

To compare daily reproductive hormone secretion in regularly menstruating older versus younger women. This was a prospective cohort study. Daily morning urine samples were obtained from 106 women, 28 of whom were aged between 20 and 34 years (mean: 27.8+/-3.7 y) and 78 of whom were aged between 35 and 50 years (mean: 40.3+/-3.7 y). Lower luteal estrone-3-glucuronide levels were seen in the older versus the younger group (82.7 vs 93.5 ng/ml, P=0.035). The pregnanediol-3-glucuronide levels in the older group were lower than those in the younger group throughout the entire cycle. The median length of the follicular phase was shorter in the older versus younger women (13 vs 14.5 d, P=0.005). There was no significant difference in the median luteal phase lengths between groups. We report the new finding that regularly menstruating older women not only have lower pregnanediol-3-glucuronide levels but also have a significant reduction in luteal phase estrone-3-glucuronide compared with a contemporaneous cohort of younger women. This combined deficit may play a key role during the luteal-follicular transition, potentially affecting follicle recruitment and decreasing fecundity in the subsequent cycle.

Ovarian feedback, mechanism of action and possible clinical implications

The secretion of gonadotrophins from the pituitary in women is under ovarian control via negative and positive feedback mechanisms. Steroidal and non-steroidal substances mediate the ovarian effects on the hypothalamic-pituitary system. During the follicular phase of the cycle, estradiol (E(2)) plays a key role, while circulating progesterone (at low concentrations) and inhibin B contribute to the control of LH and FSH secretion respectively. During the luteal phase, both E(2) and progesterone regulate secretion of the two gonadotrophins, while inhibin A plays a role in FSH secretion. The intercycle rise of FSH is related to changes in the levels of the steroidal and non-steroidal substances during the luteal-follicular transition. In terms of the positive feedback mechanism, E(2) is the main component sensitizing the pituitary to GnRH. Activity of a non-steroidal ovarian substance, named gonadotrophin surge-attenuating factor (GnSAF), has been detected after ovarian stimulation. It is hypothesized that GnSAF, by antagonizing the sensitizing effect of E(2) on the pituitary, regulates the amplitude of the endogenous LH surge at midcycle. Disturbances in the feedback mechanisms can occur in various abnormal conditions or after treatment with pharmaceutical compounds that interfere with the production or the action of endogenous hormones.

Anti-Müllerian hormone: clinical insights into a promising biomarker of ovarian follicular status

In contrast to most hormonal biomarkers of the follicular status, anti-Müllerian hormone (AMH) is exclusively produced by the granulosa cells of a wide range of follicles (primary to the early antral stages), presumably FSH-independently and with little susceptibility to disorders of antral follicle growth during the luteal–follicular transition. This paper summarizes the authors’ clinical research on the role of AMH as a marker of ovarian functioning. It shows that the relationship between antral follicle counts and serum AMH concentrations is stronger than that observed with FSH, inhibin B and oestradiol on day 3, and that intercycle reproducibility of AMH measurements is better than the latter parameters. In addition, peripheral AMH concentrations decline during ovarian stimulation, thus confirming that maturing follicles loose progressively their ability to produce AMH. Indeed, follicular fluid (FF) AMH concentrations in small antral follicles are 3-fold as high as AMH in pre-ovulatory follicles. Further, human chorionic gonadotrophin-driven luteinization additionally curtails follicular AMH production. Finally, AMH production measured in FF from individual follicles is increased in women having normal follicular counts and responsiveness to ovarian stimulation. Together, these data reinforce the soundness of AMH measurements as a quantitative and possibly qualitative marker of granulosa cell activity and health.

Predictability of Peripheral of FSH but Also Inhibin B Levels May be Altered by Early Follicle Development on Day 3

During the luteal-follicular transition of the menstrual cycle, inhibin B, a follicle-derived protein, modulates its own stimulation by FSH. Moreover, ovarian inhibin B production may be influenced not only by the number of FSH-sensitive follicles but also by their developmental status (Groome et al., 1996). This issue is particularly key in ovarian-aged women suffering from accelerated or premature follicle growth during the luteal-follicular transition and provide a plausible explanation for the debatable predictability of inhibin B (Corson et al., 1999) and FSH (Bancsi et al., 2000) on the ovarian follicular status.

The onset of the initial rise in follicle-stimulating hormone during the human menstrual cycle.

The rise in FSH (FSHr) that leads to the recruitment of a cohort of follicles during the menstrual cycle occurs during the luteal-follicular transition, however, it is unclear whether it consistently occurs on one particular day, or is subjected to reproductive ageing. We determined the FSHr in 836 complete menstrual cycles from 102 women with regular menses using an algorithm, and additionally compared the relative variation in FSH during the last 14 days of the cycle. Possible effects of reproductive ageing on the onset of FSHr were also investigated. The day of FSHr follows a normal distribution with a median value of -4 (relative to first day of menses), mean -4.1 and SD 2.1. Analysis of the relative changes in FSH during the last 14 days of the cycle revealed the first significant rise on day -4 (P=0.0033), coinciding with the first significant drop in estrogens (P=0.0002). No effect of chronological age, or initial FSH levels, on FSHr was found, however, there was an inverse relationship between total follicular phase length (from day of FSHr to LH peak) and initial FSH levels (P<0.0001). The initial FSH rise in the cycle occurs consistently 4 days before menses, is related to a drop in estrogen levels, and is not affected by reproductive ageing.

Menstrual disturbances in athletes: a focus on luteal phase defects.

Subtle menstrual disturbances that affect the largest proportion of physically active women and athletes include luteal phase defects (LPD). Disorders of the luteal phase, characterized by poor endometrial maturation as a result of inadequate progesterone (P4) production and short luteal phases, are associated with infertility and habitual spontaneous abortions. In recreational athletes, the 3-month sample prevalence and incidence rate of LPD and anovulatory menstrual cycles is 48% and 79%, respectively. A high proportion of active women present with LPD cycles in an intermittent and inconsistent manner. These LPD cycles are characterized by reduced follicle-stimulating hormone (FSH) during the luteal-follicular transition, a somewhat blunted luteinizing hormone surge, decreased early follicular phase estradiol excretion, and decreased luteal phase P4 excretion both with and without a shortened luteal phase. LPD cycles in active women are associated with a metabolic hormone profile indicative of a hypometabolic state that is similar to that observed in amenorrheic athletes but not as comprehensive or severe. These metabolic alterations include decreased serum total triiodothyronine (T3), leptin, and insulin levels. Bone mineral density in these women is apparently not reduced, provided an adequate estradiol environment is maintained despite decreased P4. The high prevalence of LPD warrants further investigation to assess health risks and preventive strategies.

Control of follicle-stimulating hormone by estradiol and the inhibins: critical role of estradiol at the hypothalamus during the luteal-follicular transition.

To test the hypothesis that estradiol, inhibin A, and inhibin B contribute differentially to FSH negative feedback in specific phases of the menstrual cycle, daily blood samples were obtained across a control cycle and after selective estrogen blockade with tamoxifen. To examine the site of estradiol-negative feedback in control and tamoxifen treatment cycles, early follicular phase GnRH (free alpha-subunit) pulse frequency was assessed in normal women, and FSH levels were examined in GnRH-deficient women in whom hypothalamic output was fixed with GnRH administration. FSH was higher in the early follicular phase in the presence of estrogen receptor blockade (15.7 +/- 3.1 vs. 13.2 +/- 1.9 IU/liter; P < 0.05) but was not increased in the late follicular phase. In the luteal phase, FSH was elevated (10.1 +/- 0.7 vs. 7.3 +/- 0.6 IU/liter; P < 0.01). In normal women, free alpha-subunit pulse frequency increased (7.3 +/- 0.4 vs. 4.8 +/- 0.4 pulses per 8 h; P < 0.003), but in GnRH-deficient women, there was no FSH increase (11.1 +/- 1.6 vs. 12.5 +/- 3.6 IU/liter) in the early follicular phase in the presence of estrogen blockade. In conclusion, estradiol exerts a greater role over inhibin in FSH-negative feedback regulation during the luteal phase and the luteal-follicular transition. In contrast, inhibin A and/or B plays a more critical role as the follicular phase progresses. In addition, these studies support a primary if not exclusive hypothalamic site of estrogen-negative feedback in the early follicular phase.

Beneficial effects of GnRH agonist administration prior to ovarian stimulation for patients with a short follicular phase

A short follicular phase is an early clinical feature of declining reproductive competence. The shortening of the follicular phase length is related to both advanced recruitment and selection of the dominant follicle secondary to an earlier and higher FSH rise during the luteal–follicular transition, while the late follicular growth is normal. As a short follicular phase may be detrimental for reproduction, it was postulated that increasing the duration of follicular phase could improve conception rate. For that purpose, gonadotrophin-releasing hormone agonist minidoses were administered in the mid-luteal phase to prevent the intercycle FSH rise before tailoring follicular growth by controlled exogenous FSH administration. This regimen, applied to 69 infertile ovulatory women with a short follicular phase (9.6 ± 1.2 days) actually lengthened the follicular phase by about 3 days. It proved to be effective in 179 cycles to induce paucifollicular development (1.8 ± 0.9 follicles) with a low cancellation rate (4%) and a moderate requirement for gonadotrophins [13.3 ± 6.3 ampoules (75 IU)]. In those women with a high frequency (80%) of elevated basal FSH or oestradiol concentrations, the pregnancy rate reached 15.1%/cycle but the miscarriage rate remained high (44%). Thus, increasing the follicular phase length in patients with a short follicular phase may partially restore fecundity.

Hypothalamic Regulation of Cyclic Ovulation: Evidence That the Increase in Gonadotropin-Releasing Hormone Pulse Frequency during the Follicular Phase Reflects the Gradual Loss of the Restraining Effects of Progesterone

The luteal-follicular transition is characterized by decreasing plasma levels of E2, progesterone (P), and inhibin A, with concomitant increases in FSH and LH levels. LH (and by inference GnRH) pulse frequency increases from 1 pulse every 3–4 h during the luteal phase to approximately 1 pulse/h at the midcycle LH surge. To examine the regulation of GnRH pulse frequency, we gave 10 normally cycling women transdermal E2 and oral P to produce midluteal levels [364 ± 65.0 pmol/liter (99 ± 18 pg/ml) and 29.7 ± 6.8 nmol/liter (9.3 ± 2.1 ng/ml), respectively] for 10 d after the LH surge (d 0). P was then discontinued, and E2 was given alone for 3 additional wk. Pulsatile LH secretion and follicular size were assessed on d 10, 17, 24, and 31. Results are presented as the mean ± sem. LH pulse frequency was 3.1 ± 0.5 pulses/12 h after 10 d of E2 and P, and remained low on d 17 when P had fallen below 1.6 nmol/liter (<0.5 ng/ml). In the continued presence of midluteal levels of E2 [∼360 pmol/liter (100 pg/ml)], LH pulse frequency increased on d 24 and 31 to 5.5 ± 0.9 and 5.8 ± 0.5 pulses/12 h, respectively, whereas pulse amplitude remained unchanged. FSH increased 2-fold, but follicular size did not change. These results are consistent with E2 potentiating the effects of low concentrations of P on the GnRH pulse generator for at least 7 d, after which pulse frequency increases despite maintenance of E2 levels. This supports the hypothesis that the increasing GnRH pulse frequency throughout the follicular phase reflects the gradual loss of the inhibitory actions of low concentrations of P.

Hypothalamic regulation of cyclic ovulation: evidence that the increase in gonadotropin-releasing hormone pulse frequency during the follicular phase reflects the gradual loss of the restraining effects of progesterone.

The luteal-follicular transition is characterized by decreasing plasma levels of E(2), progesterone (P), and inhibin A, with concomitant increases in FSH and LH levels. LH (and by inference GnRH) pulse frequency increases from 1 pulse every 3-4 h during the luteal phase to approximately 1 pulse/h at the midcycle LH surge. To examine the regulation of GnRH pulse frequency, we gave 10 normally cycling women transdermal E(2) and oral P to produce midluteal levels [364 +/- 65.0 pmol/liter (99 +/- 18 pg/ml) and 29.7 +/- 6.8 nmol/liter (9.3 +/- 2.1 ng/ml), respectively] for 10 d after the LH surge (d 0). P was then discontinued, and E(2) was given alone for 3 additional wk. Pulsatile LH secretion and follicular size were assessed on d 10, 17, 24, and 31. Results are presented as the mean +/- SEM. LH pulse frequency was 3.1 +/- 0.5 pulses/12 h after 10 d of E(2) and P, and remained low on d 17 when P had fallen below 1.6 nmol/liter (<0.5 ng/ml). In the continued presence of midluteal levels of E(2) [ approximately 360 pmol/liter (100 pg/ml)], LH pulse frequency increased on d 24 and 31 to 5.5 +/- 0.9 and 5.8 +/- 0.5 pulses/12 h, respectively, whereas pulse amplitude remained unchanged. FSH increased 2-fold, but follicular size did not change. These results are consistent with E(2) potentiating the effects of low concentrations of P on the GnRH pulse generator for at least 7 d, after which pulse frequency increases despite maintenance of E(2) levels. This supports the hypothesis that the increasing GnRH pulse frequency throughout the follicular phase reflects the gradual loss of the inhibitory actions of low concentrations of P.

Regulation of gonadotropin secretion: implications for polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is a disorder characterized by hyperandrogenism and chronic anovulation. Although the etiology of PCOS is unknown, perturbations of gonadotropin secretion are one of the hallmarks of this disorder. In normal menstrual physiology, the monotropic rise of plasma follicle-stimulating hormone (FSH) during the luteal-follicular transition is critical for follicular development and subsequent ovulation. One of the mechanisms by which FSH is differentially synthesized involves the luteal slowing of gonadotropin-releasing hormone (GnRH) pulse frequency by ovarian steroids. In PCOS, plasma leutinizing hormone (LH) is commonly increased, FSH is typically in the lower follicular range, and LH (and by inference GnRH) pulse frequency is persistently rapid at approximately one LH pulse per hour. The etiology of the neuroendocrine abnormalities in PCOS remain unclear; however, recent studies have revealed decreased sensitivity of the GnRH pulse generator to inhibition by ovarian steroids, particularly progesterone. This abnormality is reversed by the androgen receptor antagonist flutamide, suggesting that elevated androgen levels may alter the sensitivity of the hypothalamic GnRH pulse generator to steroid inhibition and lead to enhanced LH secretion. As such, women with PCOS require higher levels of progesterone to slow the frequency of GnRH pulse secretion, resulting in inadequate FSH synthesis and persistent LH stimulation of ovarian androgens. The decreased sensitivity of the GnRH pulse generator may help to explain the genesis of PCOS during puberty. In normal early puberty, sleep-entrained increases in LH stimulate ovarian steroids, which subsequently suppress LH frequency and amplitude during the subsequent day. In hyperandrogenemic girls destined to develop PCOS, this nocturnal increase in ovarian steroids may not be adequate to suppress the GnRH pulse generator, leading to a persistently rapid LH pulse frequency, impaired FSH production, and inadequate follicular development.