Comparative Bioavailability of Two Daily Subcutaneous Doses Versus a Single Dose of Intramuscular and Vaginal Progesterone Formulations in Healthy Postmenopausal Females

Progesterone is a naturally occurring endocrine hormone. It is used for luteal phase support to improve success rates in assisted reproduction. This was a single-center, comparative bioavailability, open-label, randomized, 3-period, 6-sequence, crossover study to compare the rate and extent of absorption of subcutaneous (SC) progesterone 25 mg twice daily, versus vaginal (Vag) gel once daily (90 mg progesterone) and 50 mg of intramuscular (IM) progesterone injection once daily in healthy postmenopausal females. Eighteen healthy, postmenopausal, female nonsmokers aged 55-65 years were dosed. Data from 17 subjects who completed at least 2 study periods, including the test and 1 reference, were included in the pharmacokinetic analysis. The SC progesterone product administered twice daily showed a higher exposure than a single dose of the Vag formulation, with least-squares mean (LSM) ratios (SC/Vag gel) of 219.7% for AUC0-inf and 391.8% for Cmax . The SC progesterone product administered twice daily showed comparable extent of exposure to that of the IM product, but showed higher peak concentration, with LSM ratios (SC/IM) of 92.4% for AUC0-inf and 138.0% for Cmax . Mean (SD) relative bioavailability (Frel ) for SC/Vag gel was 449.6 (233.1)%, and for SC/IM was 92.3 (6.3)%. Mild injection site reactions were reported with similar frequency for SC and IM progesterone. With further research, twice-daily SC progesterone may offer an alternative to existing available treatments for luteal phase support.

Endometrial thickness on the day of embryo transfer is a poor predictor of IVF treatment outcome

STUDY QUESTION

What is the independent contribution of endometrial thickness (EMT) on day of embryo transfer to achieving an ongoing pregnancy and live birth after IVF treatment?

SUMMARY ANSWER

EMT is a poor predictor of IVF success and has only little independent prognostic value.

WHAT IS KNOWN ALREADY

In a number of previous studies, pregnancy rates have been found to be lower in patients with thin endometrium.

STUDY DESIGN SIZE DUARATION

This is a retrospective analysis of data from two large, randomized phase III studies (conducted in Europe and the USA) comparing s.c. progesterone with vaginal progesterone for luteal phase support. The studies were very similar in design, patient population and outcome, and the study data were combined and analysed on an individual patient level.

PARTICIPANTS/MATERIALS SETTING METHOD

Subjects were infertile patients with an indication for IVF/ICSI, aged between 18 and 42 years, BMI <30 kg/m², <3 prior ART cycles and ≥ 3 oocytes after controlled ovarian stimulation with GnRH-agonist or GnRH-antagonist. EMT was assessed on day of embryo transfer (n = 1401). The association of EMT and ongoing pregnancy rate was determined by comparison of outcomes by quantiles of EMT. The predictive capacity of EMT for ongoing pregnancy achievement was assessed at each millimeter cut-off. Finally, a regression model was built to determine the contribution of EMT among other confounders, such as age and oocyte numbers, on the likelihood of ongoing pregnancy and live birth.

MAIN RESULTS AND THE ROLE OF CHANCE

In univariate analysis, ongoing pregnancy rates correlate to EMT. In patients above a cut-off of ≥9 mm EMT, the chance of pregnancy was higher as compared to patients with an EMT of 3-8 mm (odds ratio (OR) = 1.69, 95% CI: 1.23-2.35, P = 0.001; sensitivity 88.89%, specificity 17.52%, positive predictive value 39.02%, negative predictive value 72.64% and likelihood ratio 1.08). In multivariate regression analysis, after controlling for trial, female age and oocyte numbers, EMT was a statistically significant predictor of live birth (OR = 1.05, 95% CI: 1.00-1.10; P = 0.0351). If EMT indeed is an independent factor affecting outcome, this finding implies that at a baseline live birth rate of 20% an increase of 2 mm in EMT should result in an increase of the live birth rate of ~1.6%.

LIMITATIONS REASONS FOR CAUTION

The independent contribution of EMT to live birth likelihood is small and may result from (undetermined) confounding. The EMT on day of embryo transfer is usually higher as compared to the EMT on day of triggering final oocyte maturation when it is conventionally assessed during routine cycle monitoring. Furthermore, endometrial lining pattern and/or subendometrial Doppler flow have not been assessed and, accordingly, the conclusions of this work are limited to only the thickness of the endometrium.

WIDER IMPLICATIONS OF THE FINDINGS

EMT can be ignored during cycle monitoring of the majority of IVF patients and only the extremes of EMT deserve further diagnostic work-up.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by IBSA. G.G. has received personal fees and non-financial support from MSD, Ferring, Merck-Serono, Finox, TEVA, IBSA, Glycotope, Abbott, Gedeon-Richter as well as personal fees from VitroLife, NMC Healthcare, ReprodWissen, BioSilu and ZIVA. S.T. and B.C. are employees of IBSA.

TRIAL REGISTRATION NUMBER

NCT00827983 and NCT00828191 (clinicaltrials.gov).

Trial registration date

23 January 2009 (NCT00827983 and NCT00828191).

DATE OF FIRST PATIENT’S ENROLMENT

January 2009 (NCT00827983 and NCT00828191).

Assessment of the immunogenicity of gonadotrophins during controlled ovarian stimulation

Problem

Gonadotrophin hormones are used for the controlled ovarian stimulation (COS) as part of the in vitro fertilization techniques. Therapeutic proteins have the potential to induce an unwanted immune response.

Method of study

The presence of anti‐FSH, anti‐LH and anti‐hCG antibodies were determined in patients from two different clinical trials after the repeated administration of hMG or FSH.

Results

In the first study, 27 subjects were screening for the presence of anti‐FSH antibodies. From the 27 patients, only one patient showed the presence of low levels of antibodies. In a second study, 25 patients were screened for the presence of anti‐FSH, anti‐LH and anti‐hCG antibodies. At the end of the study, no patients showed the presence of antibodies.

Conclusion

The results of this study suggest that repeated treatment cycles with FSH or hMG in patients undergoing COS for in vitro fertilization can be safely and effectively applied without concerns for immunogenicity.

Subcutaneous Progesterone Is Effective and Safe for Luteal Phase Support in IVF: An Individual Patient Data Meta-Analysis of the Phase III Trials

Objective

To summarize efficacy and safety data on a new progesterone compound which is available for subcutaneous administration as compared to vaginally administered progesterone for luteal phase support in patients undergoing IVF treatment.

Design

Data from two randomized phase III trials (07EU/Prg06 and 07USA/Prg05) performed according to GCP standards with a total sample size of 1435 per-protocol patients were meta-analyzed on an individual patient data level.

Setting

University affiliated reproductive medicine unit.

Patients

Subcutaneous progesterone was administered to a total of 714 subjects and vaginal progesterone was administered to a total of 721 subjects who underwent fresh embryo transfer after ovarian stimulation followed by IVF or ICSI. The subjects were between 18 and 42 years old and had a BMI <30kg/m².

Interventions

Subcutaneous progesterone 25 mg daily vs. either progesterone vaginal gel 90 mg daily (07EU/Prg06) or 100 mg intravaginal twice a day (07USA/Prg05) for luteal phase support in IVF patients.

Main outcome measures

Ongoing pregnancy rate beyond 10 gestational weeks, live birth rate and OHSS risk.

Results

The administration of subcutaneous progesterone versus intra-vaginal progesterone had no impact on ongoing pregnancy likelihood (OR = 0.865, 95% CI 0.694 to 1.077; P = n.s.), live birth likelihood (OR = 0.889, 95% CI 0.714 to 1.106; P = n.s.) or OHSS risk (OR = 0.995, 95% CI 0.565 to 1.754; P = n.s.) in regression analyses accounting for clustering of patients within trials, while adjusting for important confounders. Only female age and number of oocytes retrieved were significant predictors of live birth likelihood and OHSS risk.

Conclusion

No statistical significant or clinical significant differences exist between subcutaneous and vaginal progesterone for luteal phase support.

Pharmaceutical and clinical development of a novel progesterone formulation

Progesterone plays an essential role in reproductive events. Its use for luteal support in patients undergoing infertility treatment is an established practice. The different routes used to administer progesterone impact on its efficacy in luteal support: oral administration has been shown to be ineffective due to an extensive first-pass metabolism in the liver; vaginal application has a good efficacy but has drawbacks such as vaginal leakage, irritation, discomfort and uncertainty about the real dose adsorbed; finally, intramuscular administration ensures a precise dosage but can be extremely painful with, in some cases, formation of sterile abscesses. A new progesterone preparation is now available in several European and extra-European countries that combines the precise dosage of the injectable formulation with the comfort of a well-tolerated subcutaneous self-administration. The pharmacokinetic and pharmacodynamic properties of this new product are reviewed here, together with the clinical evidence obtained in two multicenter randomized clinical trials.

A randomized, controlled trial comparing the efficacy and safety of aqueous subcutaneous progesterone with vaginal progesterone for luteal phase support of in vitro fertilization

STUDY QUESTION

Is the ongoing pregnancy rate with a new aqueous formulation of subcutaneous progesterone (Prolutex(®)) non-inferior to vaginal progesterone (Endometrin(®)) when used for luteal phase support of in vitro fertilization?

SUMMARY ANSWER

In the per-protocol (PP) population, the ongoing pregnancy rates per oocyte retrieval at 12 weeks of gestation were comparable between Prolutex and Endometrin (41.6 versus 44.4%), with a difference between groups of -2.8% (95% confidence interval (CI) -9.7, 4.2), consistent with the non-inferiority of subcutaneous progesterone for luteal phase support.

WHAT IS KNOWN ALREADY

Luteal phase support has been clearly demonstrated to improve pregnancy rates in women undergoing in vitro fertilization (IVF). Because of the increased risk of ovarian hyperstimulation syndrome associated with the use of hCG, progesterone has become the treatment of choice for luteal phase support.

STUDY DESIGN, SIZE, DURATION

This prospective, open-label, randomized, controlled, parallel-group, multicentre, two-arm, non-inferiority study was performed at eight fertility clinics. A total of 800 women, aged 18-42 years, with a BMI of ≤ 30 kg/m(2), with <3 prior completed assisted reproductive technology (ART) cycles, exhibiting baseline (Days 2-3) FSH of ≤ 15 IU/L and undergoing IVF at 8 centres (seven private, one academic) in the USA, were enrolled from January 2009 through June 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 800 women undergoing IVF were randomized after retrieval of at least three oocytes to an aqueous preparation of progesterone administered subcutaneously (25 mg daily) or vaginal progesterone (100 mg bid daily). Randomization was performed to enrol 100 patients at each site using a randomization list that was generated with Statistical Analysis Software (SAS(®)). If a viable pregnancy occurred, progesterone treatment was continued up to 12 weeks of gestation.

MAIN RESULTS AND THE ROLE OF CHANCE

Using a PP analysis, which included all patients who received an embryo transfer (Prolutex = 392; Endometrin = 390), the ongoing pregnancy rate per retrieval for subcutaneous versus vaginal progesterone was 41.6 versus 44.4%, with a difference between groups of -2.8% (95% CI -9.7, 4.2), consistent with the non-inferiority of subcutaneous progesterone for luteal phase support. In addition, rates of initial positive β-hCG (56.4% subcutaneous versus 59.0% vaginal; 95% CI -9.5, 4.3), clinical intrauterine pregnancy with fetal cardiac activity (42.6 versus 46.4%; 95% CI -10.8, 3.2), implantation defined as number of gestational sacs divided by number of embryos transferred (33.2 versus 35.1%; 95% CI -7.6, 4.0), live birth (41.1 versus 43.1%; 95% CI -8.9, 4.9) and take-home baby (41.1 versus 42.6%; 95% CI -8.4, 5.4) were comparable. Both formulations were well-tolerated, with no difference in serious adverse events. Analysis with the intention-to-treat population also demonstrated no difference for any outcomes between the treatment groups.

LIMITATIONS, REASONS FOR CAUTION

The conclusions are limited to the progesterone dosing regimen studied and duration of treatment for the patient population examined in this study.

WIDER IMPLICATIONS OF THE FINDINGS

Subcutaneous progesterone represents a novel option for luteal phase support in women undergoing IVF who for personal reasons prefer not to use a vaginal preparation or who wish to avoid the side effects of vaginal or i.m. routes of administration.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by Institut Biochimique SA (IBSA). CAJ, BC, ST and CJ are employees of IBSA. FH currently consults for IBSA.

TRIAL REGISTRATION NUMBER

NCT00828191.

Subcutaneous progesterone versus vaginal progesterone gel for luteal phase support in in vitro fertilization: a noninferiority randomized controlled study

OBJECTIVE

To compare the safety, efficacy, and tolerability of subcutaneous progesterone (Prolutex, 25 mg; IBSA Institut Biochimique SA) with vaginal progesterone gel (Crinone, 8%; Merck Serono) for luteal phase support (LPS) in assisted reproduction technologies (ART) patients.

DESIGN

Prospective, open-label, randomized, controlled, parallel-group, multicenter, two-arm, noninferiority study.

SETTING

Thirteen European fertility clinics.

PATIENT(S)

A total of 683 ART patients randomized to two groups: Prolutex, 25 mg subcutaneously daily (n = 339); and Crinone, 90 mg 8% gel daily (n = 344).

INTERVENTION(S)

In vitro fertilization and embryo transfer were performed according to site-specific protocols. On the day of oocyte retrieval, Prolutex or Crinone gel was begun for LPS and continued for up to 10 weeks.

MAIN OUTCOME MEASURE(S)

Ongoing pregnancy rate.

RESULT(S)

The primary end point, ongoing pregnancy rates at 10 weeks of treatment were 27.4% and 30.5% in the Prolutex and Crinone groups, respectively (intention to treat [ITT]). The nonsignificant difference between the groups was -3.09% (95% confidence interval [CI] -9.91-3.73), indicating noninferiority of Prolutex to Crinone. Delivery and live birth rates resulted to be equivalent between the two treatments (26.8% vs. 29.9% in the Prolutex and Crinone groups, respectively [ITT]; difference -3.10 [95% CI -9.87-3.68]). No statistically significant differences were reported for any of the other secondary efficacy endpoints, including comfort of usage and overall satisfaction.

CONCLUSION(S)

Implantation rate, pregnancy rate, live birth rate, and early miscarriage rate for Prolutex were similar to those for Crinone. The adverse event profiles were similar and Prolutex was safe and well tolerated.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00827983.

A prospective, randomised, investigator-blind, controlled, clinical study on the clinical efficacy and tolerability of two highly purified hMG preparations administered subcutaneously in women undergoing IVF

The aim of this multicentre, prospective, randomised, investigator blind, controlled clinical trial was to evaluate the clinical efficacy and tolerability of a highly purified human menopausal gonadotrophin (hMG) preparation (Merional-HG) when administered to patients undergoing controlled ovarian stimulation (COS) for in-vitro fertilisation (IVF) procedure enrolled in hospital departments. One hundred fifty-seven patients were randomised in two parallel groups: 78 started COS with Merional-HG and 79 with Menopur. Results of the study showed that both highly purified hMG preparations were equivalent in terms of number of oocytes retrieved (primary endpoint: 8.8 ± 3.9 versus 8.4 ± 3.8, p = 0.54). In the patients treated with Merional-HG, we observed a higher occurrence of mature oocytes (78.3% versus 71.4%, p = 0.005) and a reduced quantity of gonadotrophins administered per cycle (2.556 ± 636 IU versus 2.969 ± 855 IU, p < 0.001). Fertilisation, cleavage, implantation rates and the number of positive β-human chorionic gonadotrophin (hCG; pregnancy) tests and the clinical pregnancy rate were comparable in the two groups. Both treatments were well tolerated. In conclusion, the results of this study support the efficacy and safety of Merional-HG administered subcutaneously for assisted reproduction techniques. Efficiency of Merional-HG appears to be higher due to reduced quantity of drug used and the higher yield of mature oocytes retrieved.

A randomized trial comparing the endometrial effects of daily subcutaneous administration of 25 mg and 50 mg progesterone in aqueous preparation

OBJECTIVE

To study the efficacy of a new P preparation in aqueous solution for subcutaneous injection for inducing the predecidual transformation of the endometrium.

DESIGN

Prospective, single-blinded, randomized, parallel pilot trial.

SETTING

University-affiliated clinical research center.

PATIENT(S)

Twenty-five regularly cycling female volunteers.

INTERVENTION(S)

Volunteers, aged 18-45 years, body mass index 19-25 kg/m(2), whose ovaries were suppressed with a GnRH agonist were estrogenized for 14 or 21 days with the use of transdermal systems delivering 0.1 mg/d E₂. After confirming that the endometrial thickness was >7 mm, the women were randomized to 25 mg or 50 mg of subcutaneous P injections daily for 11 days, after which the endometrium was sampled with the use of a Pipelle device. The endometrial biopsies were evaluated by two independent pathologists. Adverse events and subjective tolerance were checked every day by the study investigator.

MAIN OUTCOME MEASURE(S)

Predecidual changes in endometrial biopsies obtained after 11 days of subcutaneous administration of P.

RESULT(S)

Of 24 biopsies performed (one dropout), 22 provided tissue for histologic analysis. Evidence of predecidual changes in the endometrial stroma was found in 100% of the cases, with no differences between the two studied doses.

CONCLUSION(S)

Both doses of the new aqueous P preparation available for subcutaneous administration demonstrated predecidual changes in 100% of the interpretable endometrial biopsies in total absence of endogenous P. This offers good prospect of efficacy in luteal phase support for the lowest dose tested, 25 mg/d, the physiologic amount produced daily by the ovary during the midluteal phase.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00377923.

Pharmacokinetics and safety profile of a novel progesterone aqueous formulation administered by the s.c. route

A novel aqueous progesterone formulation was developed. Study I: Three-way cross-over, open-label study in 24 post-menopausal women. Comparison of the pharmacokinetic profiles of a single 100 mg dose of test product administered by subcutaneous (s.c.) and intramuscular (i.m.) injection and an i.m. reference oily product. Study II: Three-way cross-over open-label study of 25, 50 and 100 mg s.c. single doses of the aqueous formulation in 12 post-menopausal women. Study III: Parallel-group, observer-blinded study in 25 fertile women administered multiple s.c. 25 and 50 mg doses of the aqueous formulation once daily for 11 days. Baseline-corrected pharmacokinetic parameters were evaluated. Aqueous formulation (100 mg) was promptly absorbed, achieving progesterone peak serum levels at an earlier time than the reference (1 h vs. 7 h; p < 0.0001). Test and reference were bioequivalent in the extent of exposure: confidence intervals for AUC(0-t) geometric means ratios were within the pre-specified 80-125% limits. Pharmacokinetics was linear over the range of doses studied. Steady state was reached within 4 days of multiple dose treatment. All treatments were well tolerated. Considering the advantages given by the possibility of self-medication, the s.c. aqueous formulation could offer a convenient alternative for patients on assisted reproductive technology treatments.

Factors affecting success rates in two concurrent clinical IVF trials: an examination of potential explanations for the difference in pregnancy rates between the United States and Europe

OBJECTIVE

To compare a US clinical trial of gonadotropin therapy for IVF with a similar European trial to determine what factors may explain the higher clinical pregnancy rate in the US trial.

DESIGN

Comparison of baseline, treatment, and outcome variables in the United States (US) and European trials.

SETTING

IVF practices in the US (n=4) and Europe (n=6).

PATIENT(S)

297 women undergoing IVF.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Clinical pregnancy rate.

RESULT(S)

Clinical pregnancy rates were 43.4% in the US compared with 29.7% in Europe (p=0.016), with a live birth rate of 38.2% versus 27.6% (p=0.064). This difference in clinical pregnancy rate could not be explained by differences in the US versus Europe for number of embryos transferred (2.3 vs. 2.6) or female age (34.6 vs. 30.4). Although the starting dose of gonadotropin was higher in the US trial compared with the European trial (300 versus 225 IU), the total dose of gonadotropin was only slightly higher in the US. In multiple logistic regression analysis of 81 pretransfer variables on clinical pregnancy, the only two found to be significant predictors of outcome were baseline endometrial thickness following down-regulation and number of days of gonadotropin treatment.

CONCLUSION(S)

This study suggests the possibility that US pregnancy rates may be higher in part because of differences in down-regulation or gonadotropin dosing. Other factors not assessed in these studies or in national datasets likely also contribute to the difference in pregnancy rates.

Elaboration of a working model for the involvement of inhibin A as a mediator of the preovulatory rise of progesterone levels

During the final days of follicular development, exogenously administered follicle-stimulating hormone (FSH) produces a rise in serum progesterone level. The aim of the present study was to investigate the possible source and regulation of this preovulatory progesterone surge. Four sets of matching treatments with gonadotropins for in vitro fertilization and intracytoplasmic sperm injection were selected from a cohort of 953 treatments in 244 couples. Half of these four sets of treatments were selected based on the unusual course of the progesterone concentration during follicular development. The first set of 11 cycles with early termination of gonadotropin administration for prolonged coasting were compared with a set of 12 cycles with similar estradiol levels but with uninterrupted ovarian stimulation. Another set of 12 cycles with low preovulatory progesterone levels (<2 nmol/l) were matched with ten cycles with normal preovulatory progesterone levels (>2 nmol/l). The sera of these four selected sets of treatments were stored for subsequent measurement of the concentrations of inhibin A, inhibin B, activin A and leptin. During ovarian hyperstimulation serum levels of inhibin A correlated significantly with those of progesterone (p < 0.001), whereas this correlation disappeared after the withdrawal of FSH administration. The rapid fall of progesterone levels during prolonged coasting contrasts with the continuing rise of estradiol concentration and indicates that the theca interna, not the granulosa, is the major source of preovulatory progesterone. Women failing to produce any increment of progesterone levels at the end of follicular development had significantly lower levels of inhibin A (p < 0.05), indicating that inhibin A may well be involved in mediating the signal of FSH from the granulosa to the theca interna.

Oviduct cells express the cyclic AMP-adenosine pathway

The extracellular cAMP-adenosine pathway refers to the local production of adenosine mediated by cAMP egress into the extracellular space, conversion of cAMP to AMP by ectophosphodiesterase (PDE), and the metabolism of AMP to adenosine by ecto-5'-nucleotidase. The goal of this study was to assess whether the cAMP-adenosine pathway is expressed in oviduct cells. Studies were conducted in cultured bovine oviduct cells (mixed cultures of fibroblasts and epithelial cells, 1:1 ratio). Confluent monolayers of oviduct cells were exposed to cAMP (0.01-100 micromol/L) in the presence and absence of 3-isobutyl-1-methylxanthine (IBMX, 1 mmol/L, an inhibitor of both extracellular and intracellular PDE activity), 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX, 100 micromol/L, a xanthine that can inhibit extracellular or ecto-PDE activity at high concentrations), or alpha,beta-methylene-adenosine-5'-diphosphate (AMPCP, 100 micromol/L, an ecto-5'-nucleotidase inhibitor) for 0-60 min. The medium was then sampled and assayed for AMP, adenosine, and inosine. Addition of exogenous cAMP to oviduct cells increased extracellular levels of AMP, adenosine, and inosine in a concentration- and time-dependent manner. This effect was attenuated by blockade of total (extracellular and intracellular) PDE activity (IBMX), ecto-PDE activity (DPSPX), or ecto-5'-nucleotidase (AMPCP). The functional relevance of the cAMP-adenosine pathway is supported by the findings that treatment with adenylyl cyclase stimulants (forskolin plus isoproterenol) resulted in the egress of cAMP (97% extracellular) into the extracellular space and its conversion into adenosine. The extracellular cAMP-adenosine pathway exists in oviduct cells and may play an important role in regulating the biology and physiology of the oviduct. This pathway also may play a critical role in regulating sperm function, fertilization, and early embryo development.

Differential effects of natural and environmental estrogens on endothelin synthesis in bovine oviduct cells

Endothelin-1 (ET-1), a vasoconstrictor and mitogenic peptide that plays an important role within the endocrine/reproductive system, is synthesized by oviduct cells and regulates tubal contractility. Because 17beta-estradiol (estradiol) regulates oviduct function by influencing the synthesis of autocrine/paracrine factors, estradiol may also regulate ET-1 synthesis. Furthermore, environmental estrogens (EEs; phytoestrogens and xenoestrogens), which structurally resemble estradiol and possess estrogenic activity, may mimic the effects of estradiol on ET-1 synthesis and may influence the reproductive system. Using cultures of bovine oviduct cells (epithelial cells:fibroblasts, 1:1), we investigated and compared the modulatory effects of estradiol, phytoestrogens, and xenoestrogens on ET-1 synthesis and determined whether these effects were estrogen receptor (ER) mediated. A quantitative ELISA for ET-1 in the culture medium revealed that 17beta-estradiol inhibits ET-1 synthesis in a concentration-dependent manner (4-400 nmol/L). In contrast to estradiol, ET-1 synthesis was induced in cell cultures treated with xenoestrogens in the following order of potency (0.1 micromol/L): 4-hydroxy-trichlorobiphenyl > 4-hydroxy-dichlorobiphenyl > trichlorobiphenyl. The stimulatory effects of xenoestrogens on ET-1 production were mimicked by the phytoestrogens biochanin-A and genistein but not by formononetin, equol, and daidzein. The oviduct cells expressed both ERs (alpha and beta), but the modulatory effects of estradiol, but not EEs, on ET-1 synthesis were blocked by ICI-182 780 (1 microM), a pure ER antagonist. Our results provide evidence that estradiol inhibits ET-1 synthesis in oviduct cells via an ER-dependent mechanism, whereas, EEs induce ET-1 synthesis via an ER-independent mechanism. The contrasting effects of EEs on ET-1 synthesis suggests that EEs may act as endocrine modulators/disruptors and may have deleterious effects on the reproductive system by adversely influencing the biology and physiology of the oviduct.