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.

Modulation of Cyclic AMP Levels in Fallopian Tube Cells by Natural and Environmental Estrogens.

Autocrine/paracrine factors generated in response to 17ß-estradiol (E2) within the fallopian tube (FT) facilitate fertilization and early embryo development for implantation. Since cyclic AMP (cAMP) plays a key role in reproduction, regulation of its synthesis by E2 may be of biological/pathophysiological relevance. Herein, we investigated whether cAMP production in FT cells (FTCs) is regulated by E2 and environmental estrogens (EE's; xenoestrogens and phytoestrogens). Under basal conditions, low levels of extracellular cAMP were detectable in bovine FTCs (epithelial cells and fibroblasts; 1:1 ratio). Treatment of FTCs with forskolin (AC; adenylyl cyclase activator), isoproterenol (ß-adrenoceptor agonist) and IBMX (phosphodiesterase (PDE) inhibitor) dramatically (>10 fold) increased cAMP; whereas LRE1 (sAC; soluble AC inhibitor) and 2',5'-dideoxyadenosine (DDA; transmembrane AC (tmAC)) inhibitor decreased cAMP. Comparable changes in basal and stimulated intracellular cAMP were also observed. Ro-20-1724 (PDE-IV inhibitor), but not milrinone (PDE-III inhibitor) nor mmIBMX (PDE-I inhibitor), augmented forskolin-stimulated cAMP levels, suggesting that PDE-IV dominates in FTCs. E2 increased cAMP levels and CREB phosphorylation in FTCs, and these effects were mimicked by EE's (genistein, 4-hydroxy-2',4',6'-trichlorobiphenyl, 4-hydroxy-2',4',6'-dichlorobiphenyl). Moreover, the effects of E2 and EE were blocked by the tmAC inhibitor DDA, but not by the ERα/ß antagonist ICI182780. Moreover, BAPTA-AM (intracellular-Ca2+ chelator) abrogated the effects of E2, but not genistein, on cAMP suggesting differential involvement of Ca2+. Treatment with non-permeable E2-BSA induced cAMP levels and CREB-phosphorylation; moreover, the stimulatory effects of E2 and EEs on cAMP were blocked by G15, a G protein-coupled estrogen receptor (GPER) antagonist. E2 and IBMX induced cAMP formation was inhibited by LRE1 and DDA suggesting involvement of both tmAC and sAC. Our results provide the first evidence that in FTCs, E2 and EE's stimulate cAMP synthesis via GPER. Exposure of the FT to EE's and PDE inhibitors may result in abnormal non-cyclic induction of cAMP levels which may induce deleterious effects on reproduction.

Natural and environmental oestrogens induce TGFB1 synthesis in oviduct cells.

Autocrine/paracrine factors generated in response to 17ß-oestradiol (E2), within the oviduct, facilitate early embryo development for implantation. Since transforming growth factor beta 1 (TGFB1) plays a key role in embryo implantation, regulation of its synthesis by E2 may be of biological/pathophysiological relevance. Here, we investigated whether oviduct cells synthesize TGFB1 and whether E2 and environmental oestrogens (EOEs; xenoestrogens and phytoestrogens) modulate its synthesis. Under basal conditions, bovine oviduct cells (OCs; oviduct epithelial cells and oviduct fibroblasts; 1:1 ratio) synthesized TGFB1. E2 concentration-dependent induced TGFB1 levels in OCs and these effects were mimicked by some, but not all EOEs (genistein, biochanin A and 4-hydroxy-2',4',6'-trichlorobiphenyl, 4-hydroxy-2',4',6'-dichlorobiphenyl); moreover, EOEs enhanced (P < 0.05) the stimulatory effects of E2 on TGFB1 synthesis. The OCs expressed oestrogen receptors alpha and beta and aryl hydrocarbon; moreover, co-treatment with ER antagonist ICI182780 blocked the stimulatory effects of E2 and EOEs on TGFB1 synthesis. Treatment with non-permeable E2-BSA failed to induce TGFB1, thereby ruling out the involvement of membrane ERs. Cycloheximide (protein synthesis inhibitor) blocked E2-induced TGFB1 synthesis providing evidence for de novo synthesis. The stimulatory effects of E2 and EOEs, were inhibited (P < 0.05) by MAPK inhibitor (PD98059), whereas intracellular-Ca2+ chelator (BAPTA-AM) and adenylyl cyclase inhibitor (SQ22536) abrogated the effects of E2, but not EOEs, suggesting that post-ER effects of E2 and EOEs involve different pathways. Our results provide the first evidence that in OCs, E2 and EOEs stimulate TGFB1 synthesis via an ER-dependent pathway. Exposure of the oviduct to EOEs may result in continuous/sustained induction of TGFB1 levels in a non-cyclic fashion and may induce deleterious effects on reproduction.

Pharmacokinetics and Pharmacodynamics of Follicle-Stimulating Hormone in Healthy Women Receiving Single and Multiple Doses of Highly Purified Human Menotrophin and Urofollitrophin.

BACKGROUND AND OBJECTIVE: Highly purified human menotrophin and urofollitrophin preparations obtained from human urine via a novel patented purification method have been tested over a timeframe of 14 years in the studies presented in this article. The objective of the studies was to investigate the pharmacokinetics and the pharmacodynamics of follicle-stimulating hormone (FSH) after single subcutaneous and intramuscular doses and multiple subcutaneous doses of the tested preparations in healthy fertile pituitary-suppressed women. DESIGNS: We performed five open, randomised, crossover, single-dose bioequivalence and/or bioavailability studies and one open, multiple-dose, pharmacokinetics and pharmacodynamics study. STUDY SUBJECTS AND TREATMENTS: The six studies included 121 healthy fertile women taking their usual combined oral contraceptives for 3 months before the study: Study 1: 300 international units (IU) of highly purified menotrophin as single subcutaneous and intramuscular doses. Study 2: 300 IU of highly purified menotrophin (test formulation vs. comparator) as single subcutaneous doses. Study 3: 300 IU of highly purified urofollitrophin (hp-FSH) (test formulation vs. comparator) as single subcutaneous doses. Study 4: 300 IU (2 × 150 IU vs. 4 × 75 IU) of hp-FSH as single subcutaneous doses. Study 5: 225 and 445 IU of hp-FSH as single subcutaneous doses. Study 6: daily 225 IU of hp-FSH as subcutaneous doses for 5 consecutive days. MAIN OUTCOME MEASURES: The main outcome measures were the FSH pharmacokinetic parameters, estradiol concentrations, and the number and size of the follicles. RESULTS: FSH after single subcutaneous and intramuscular injections of menotrophin or urofollitrophin attained a systemic peak (maximum) concentration (C max) that was on average consistent throughout the first four studies and ranged from 4.98 to 7.50 IU/L. The area under the plasma concentration-time curve (AUC) from administration to the last observed concentration time t (AUCt) ranged from 409.71 to 486.16 IU/L·h and the elimination half-life (t ½) ranged from 39.02 to 53.63 h. After multiple doses of urofollitrophin (225 IU) for 5 days, FSH attained a mean C max of 14.93 ± 2.92 IU/L and had an AUC during the time interval τ between two consecutive doses at steady state (AUCτ) of 322.59 ± 57.92 IU/L·h, which was similar to the mean AUCt after a single subcutaneous dose of 225 IU of urofollitrophin in study 5 (306.82 ± 68.37 IU/L·h). CONCLUSIONS: In our studies, the intramuscular and subcutaneous routes of menotrophin were equivalent; both menotrophin and urofollitrophin were bioequivalent to their marketed reference; FSH kinetic parameters following injection of urofollitrophin were dose proportional and independent from the administered concentration; and multiple doses of FSH increased estradiol levels and enhanced growth of follicles with a good dose-response correlation. Local tolerability was excellent throughout the six studies.

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 <30 kg/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 ß-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 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.

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.