Inositol triphosphate participates in an oestradiol nongenomic signalling pathway involved in accelerated oviductal transport in cycling rats

Classical Estrogen Signaling in Ciliated Epithelial Cells of the Oviduct Is Nonessential for Fertility in Female Mice

Ciliary action performs a critical role in the oviduct (Fallopian tube) during pregnancy establishment through sperm and egg transport. The disruption of normal ciliary function in the oviduct affects oocyte pick-up and is a contributing factor to female infertility. Estrogen is an important regulator of ciliary action in the oviduct and promotes ciliogenesis in several species. Global loss of estrogen receptor α (ESR1) leads to infertility. We have previously shown that ESR1 in the oviductal epithelial cell layer is required for female fertility. Here, we assessed the role of estrogen on transcriptional regulation of ciliated epithelial cells of the oviduct using single-cell RNA-sequencing analysis. We observed minor variations in ciliated cell genes in the proximal region (isthmus and uterotubal junction) of the oviduct. However, 17β-estradiol treatment had little impact on the gene expression profile of ciliated epithelial cells. We also conditionally ablated Esr1 from ciliated epithelial cells of the oviduct (called ciliated Esr1d/d mice). Our studies showed that ciliated Esr1d/d females had fertility rates comparable to control females, did not display any disruptions in preimplantation embryo development or embryo transport to the uterus, and had comparable cilia formation to control females. However, we observed some incomplete deletion of Esr1 in the ciliated epithelial cells, especially in the ampulla region. Nevertheless, our data suggest that ESR1 expression in ciliated cells of the oviduct is dispensable for ciliogenesis and nonessential for female fertility in mice.

Altered Ovarian Inositol Ratios May Account for Pathological Steroidogenesis in PCOS

The presence of abnormal ovarian ratios of myo-inositol (MI) to D-chiro-inositol (DCI) is a recurrent feature in PCOS. Available evidence suggests that MI and DCI may modulate steroid biosynthesis, likely in an opposite manner. Specifically, MI seems to induce estrogen production, while DCI has a role in the synthesis of androgens. Elevated insulin levels, generally associated with PCOS, alter the physiological MI/DCI ratio, increasing MI-to-DCI conversion through activation of a specific epimerase enzyme. DCI directly increases testosterone biosynthesis in thecal cells and reduces its conversion to estradiol by downregulating aromatase enzyme in granulosa cells. This manuscript reviews the literature that supports the connection between altered MI/DCI ratios and pathological steroidogenesis observed in PCOS women. Furthermore, it discusses the application of inositol-based treatment protocols in managing PCOS symptoms and improving the quality of patients' life.

Breakthroughs in the Use of Inositols for Assisted Reproductive Treatment (ART)

It is well known that myo-inositol (MI) and D-chiro-inositol (DCI) are insulin-sensitizing agents, and MI is of proven utility in polycystic ovary syndrome (PCOS). In addition, MI plays a pivotal role in the physiology of reproduction, and has beneficial effects on the development of oocytes, spermatozoa, and embryos. By contrast, DCI has little effect on spermatozoa, but high concentrations in the ovary can negatively affect the quality of oocytes and the blastocyst. Overall, the evidence in the literature supports the beneficial effects of MI in both female and male reproduction, warranting clinical use of MI in assisted reproductive treatment (ART).

Inositols in Polycystic Ovary Syndrome: An Overview on the Advances

This review details the physiologic roles of two insulin sensitizers, myo-inositol (MI) and d-chiro-inositol (DCI). In the human ovary, MI is a second messenger of follicle-stimulating hormone (FSH) and DCI is an aromatase inhibitor. These activities allow a treatment for polycystic ovary syndrome (PCOS) to be defined based on the combined administration of MI and DCI, where the best MI:DCI ratio is 40:1. Moreover, MI enhances the effect of metformin and clomiphene on the fertility of PCOS women seeking pregnancy. As impaired intestinal transport may lead to unsuccessful inositol treatment, we also discuss new data on the use of alpha-lactalbumin to boost inositol absorption. Overall, the physiological activities of MI and DCI dictate the dosages and timing of inositol supplementation in the treatment of PCOS.

Experts' opinion on inositols in treating polycystic ovary syndrome and non-insulin dependent diabetes mellitus: a further help for human reproduction and beyond

Introduction: This Experts' opinion provides an updated scientific support to gynecologists, obstetricians, endocrinologists, nutritionists, neurologists and general practitioners on the use of Inositols in the therapy of Polycystic Ovary Syndrome (PCOS) and non-insulin dependent (type 2) diabetes mellitus (NIDDM).Areas covered: This paper summarizes the physiology of Myo-Inositol (MI) and D-Chiro-Inositol (DCI), two important molecules present in human organisms, and their therapeutic role, also for treating infertility. Some deep differences between the physiological functions of MI and DCI, as well as their safety and intestinal absorption are discussed. Updates include new evidence on the efficacy exerted in PCOS by the 40:1 MI/DCI ratio, and the innovative approach based on alpha-lactalbumin to overcome the decreased therapeutic efficacy of Inositols in some patients.Expert opinion: The evidence suggests that MI, alone or with DCI in the 40:1 ratio, offers a promising treatment for PCOS and NIDDM. However, additional studies need to evaluate some still unresolved issues, such as the best MI/DCI ratio for treating NIDDM, the potential cost-effectiveness of reduced gonadotropins administration in IVF due to MI treatment, or the benefit of MI supplementation in ovulation induction with clomiphene citrate in PCOS patients.

The role of mating in oviduct biology

The oviduct connects the ovary to the uterus, and is subject to changes that influence gamete transport, fertilization, and early embryo development. The ovarian steroids estradiol and progesterone are largely responsible for regulating oviduct function, although mating signals also affect the female reproductive tract, both indirectly, through sensory stimulation, and directly, through contact with seminal plasma or spermatozoa. The resulting alterations in gene and protein expression help establish a microenvironment that is appropriate for sperm storage and selection, embryo development, and gamete transport. Mating may also induce the switch from a non-genomic to a genomic pathway of estradiol-accelerated oviduct egg transport, reflecting a novel example of the functional plasticity in well-differentiated cells. This review highlights the physiological relevance of various aspects of mating to oviduct biology and reproductive success. Expanding our knowledge of the mating-associated molecular and cellular events in oviduct cells would undoubtedly facilitate new therapeutic strategies to treat infertility attributable to oviduct pathologies. Mol. Reprod. Dev. 83: 875-883, 2016 © 2016 Wiley Periodicals, Inc.

Oviduct: roles in fertilization and early embryo development

Animal oviducts and human Fallopian tubes are a part of the female reproductive tract that hosts fertilization and pre-implantation development of the embryo. With an increasing understanding of roles of the oviduct at the cellular and molecular levels, current research signifies the importance of the oviduct on naturally conceived fertilization and pre-implantation embryo development. This review highlights the physiological conditions within the oviduct during fertilization, environmental regulation, oviductal fluid composition and its role in protecting embryos and supplying nutrients. Finally, the review compares different aspects of naturally occurring fertilization and assisted reproductive technology (ART)-achieved fertilization and embryo development, giving insight into potential areas for improvement in this technology.

A Randomized Pilot Study of Inositol in Association with Betaine and Boswellia in the Management of Mastalgia and Benign Breast Lump in Premenopausal Women

Benign mammary lumps and mastalgia are the most common breast disorders; yet, there is no clear-cut consensus about the best strategy for their treatment. We hypothesized that a combination, including boswellic acid, betaine, and myoinositol, would be beneficial in breast disorders by exerting a pleiotropic effect on multiple pathways. Indeed, myoinositol has already been proven to modulate some factors involved in the genesis of breast diseases, such as fibrosis and metabolic and endocrine cues. In our study, 76 women were randomly assigned to either the experimental or the placebo arm. After six months of treatment, statistically significant differences between the two groups were recorded for pain relief (56% vs 17%) and breast density reduction (60% vs 9%). Furthermore, benign breast mass dimension showed a reduction in the experimental group (40% vs 16%). The combination of boswellic acid, betaine, and myoinositol has been demonstrated to be effective in the treatment of breast pain and radiologically and histologically confirmed benign breast mass and in the reduction of breast density, one of the pivotal risk factors for the development of breast cancer, without any side effects.

Estradiol increases IP3 by a nongenomic mechanism in the smooth muscle cells from the rat oviduct

Estradiol (E2) accelerates egg transport by a nongenomic action, requiring activation of estrogen receptor (ER) and successive cAMP and IP3 production in the rat oviduct. Furthermore, E2 increases IP3 production in primary cultures of oviductal smooth muscle cells. As smooth muscle cells are the mechanical effectors for the accelerated oocyte transport induced by E2 in the oviduct, herein we determined the mechanism by which E2 increases IP3 in these cells. Inhibition of protein synthesis by Actinomycin D did not affect the E2-induced IP3 increase, although this was blocked by the ER antagonist ICI182780 and the inhibitor of phospholipase C (PLC) ET-18-OCH3. Immunoelectron microscopy for ESR1 or ESR2 showed that these receptors were associated with the plasma membrane, indicating compatible localization with E2 nongenomic actions in the smooth muscle cells. Furthermore, ESR1 but not ESR2 agonist mimicked the effect of E2 on the IP3 level. Finally, E2 stimulated the activity of a protein associated with the contractile tone, calcium/calmodulin-dependent protein kinase II (CaMKII), in the smooth muscle cells. We conclude that E2 increases IP3 by a nongenomic action operated by ESR1 and that involves the activation of PLC in the smooth muscle cells of the rat oviduct. This E2 effect is associated with CaMKII activation in the smooth muscle cells, suggesting that IP3 and CaMKII are involved in the contractile activity necessary to accelerate oviductal egg transport.

Estradiol increases cAMP in the oviductal secretory cells through a nongenomic mechanism

In the rat oviduct, estradiol (E2) accelerates egg transport by a nongenomic action that requires previous conversion of E2 to methoxyestrogens via catechol-O-methyltranferase (COMT) and activation of estrogen receptor (ER) with subsequent production of cAMP and inositol triphosphate (IP3). However, the role of the different oviductal cellular phenotypes on this E2 nongenomic pathway remains undetermined. The aim of this study was to investigate the effect of E2 on the levels of cAMP and IP3 in primary cultures of secretory and smooth muscle cells from rat oviducts and determine the mechanism by which E2 increases cAMP in the secretory cells. In the secretory cells, E2 increased cAMP but not IP3, while in the smooth muscle cells E2 decreased cAMP and increased IP3. Suppression of protein synthesis by actinomycin D did not prevent the E2-induced cAMP increase, but this was blocked by the ER antagonist ICI 182 780 and the inhibitors of COMT OR 486, G protein-α inhibitory (Gαi) protein pertussis toxin and adenylyl cyclase (AC) SQ 22536. Expression of the mRNA for the enzymes that metabolizes estrogens, Comt, Cyp1a1, and Cyp1b1 was found in the secretory cells, but this was not affected by E2. Finally, confocal immunofluorescence analysis showed that E2 induced colocalization between ESR1 (ERα) and Gαi in extranuclear regions of the secretory cells. We conclude that E2 differentially regulates cAMP and IP3 in the secretory and smooth muscle cells of the rat oviduct. In the secretory cells, E2 increases cAMP via a nongenomic action that requires activation of COMT and ER, coupling between ESR1 and Gαi, and stimulation of AC.

Mating decreases plasma levels of TGFβ1 and regulates myosalpinx expression of TGFβ1/TGFBR3 in the rat

Mating shuts down a 2-methoxyestradiol (2ME)-dependent, non-genomic activity that is responsible for accelerating egg transport in the rat oviduct. The aims of this work were to investigate the role of TGFβ1 in this 2ME-reduced activity and to determine the effect of mating on the expression and distribution of TGFβ1 and its receptor TGFBR3 in the rat oviduct. We determined the level of TGFβ1 in the plasma and oviductal fluid at 1, 3, or 6 hr during Day 1 of the oestrous cycle in unmated or mated animals. We then examined if 2ME accelerates oviductal egg transport in unmated rats that were previously treated with a neutralizing TGFβ1 antibody. The expression of Tgfb1 and Tgfbr3 mRNA and the level and distribution of TGFBR3 protein in the oviduct were also determined at these time points. Mating decreased TGFβ1 in the plasma, but not in the oviductal fluid, whereas antibody neutralization of circulating TGFβ1 did not prevent the effect of 2ME on egg transport. Mating decreased Tgfb1 and hastened the increase in TGFBR3 abundance in the myosalpinx. These results indicate that mating decreased circulating levels of TGFβ1 without shutting down the non-genomic 2ME response that normally accelerates egg transport. Levels of Tgfb1 transcript and TGFBR3 protein, however, changed in the myosalpinx of mated rats, suggesting a role for mating-associated factors in the autocrine and paracrine effects of TGFβ in the oviduct.

The rationale of the myo-inositol and D-chiro-inositol combined treatment for polycystic ovary syndrome

PCOS is one of the most common endocrine disorders affecting women and it is characterized by a combination of hyper-androgenism, chronic anovulation, and insulin resistance. While a significant progress has recently been made in the diagnosis for PCOS, the optimal infertility treatment remains to be determined. Two inositol isomers, myo-inositol (MI) and D-chiro-inositol (DCI) have been proven to be effective in PCOS treatment, by improving insulin resistance, serum androgen levels and many features of the metabolic syndrome. However, DCI alone, mostly when it is administered at high dosage, negatively affects oocyte quality, whereas the association MI/DCI, in a combination reproducing the plasma physiological ratio (40:1), represents a promising alternative in achieving better clinical results, by counteracting PCOS at both systemic and ovary level.

Tumour necrosis factor-α is the signal induced by mating to shutdown a 2-methoxyestradiol nongenomic action necessary to accelerate oviductal egg transport in the rat

Mating shut down a 2-methoxyestradiol (2ME) nongenomic action necessary to accelerate egg transport in the rat oviduct. Herein, we investigated whether tumour necrosis factor-α (TNF-α) participates in this mating effect. In unmated and mated rats, we determined the concentration of TNF-α in the oviductal fluid and the level of the mRNA for Tnf-a (Tnf) and their receptors Tnfrsf1a and Tnfrsf1b in the oviduct tissues. The distribution of the TNFRSF1A and TNFRSF1B proteins in the oviduct of unmated and mated was also assessed. Finally, we examined whether 2ME accelerates oviductal egg transport in unmated rats that were previously treated with a rat recombinant TNF-α alone or concomitant with a selective inhibitor of the NF-κB activity. Mating increased TNF-α in the oviductal fluid, but Tnf transcript was not detected in the oviduct. The mRNA for TNF-α receptors as well as their distribution was not affected by mating, although they were mainly localized in the endosalpinx. Administration of TNF-α into the oviduct of unmated rats prevented the effect of 2ME on egg transport. However, the NF-κB activity inhibitor did not revert this effect of TNF-α. These results indicate that mating increased TNF-α in the oviductal fluid, although this not associated with changes in the expression and localization of TNF-α receptors in the oviductal cells. Furthermore, TNF-α mimicked the effect of mating on the 2ME-induced egg transport acceleration, independently of the activation of NF-κB in the oviduct. We concluded that TNF-α is the signal induced by mating to shut down a 2ME nongenomic action in the rat oviduct.

The role of purinergic signaling on deformation induced injury and repair responses of alveolar epithelial cells

Cell wounding is an important driver of the innate immune response of ventilator-injured lungs. We had previously shown that the majority of wounded alveolus resident cells repair and survive deformation induced insults. This is important insofar as wounded and repaired cells may contribute to injurious deformation responses commonly referred to as biotrauma. The central hypothesis of this communication states that extracellular adenosine-5′ triphosphate (ATP) promotes the repair of wounded alveolus resident cells by a P2Y2-Receptor dependent mechanism. Using primary type 1 alveolar epithelial rat cell models subjected to micropuncture injury and/or deforming stress we show that 1) stretch causes a dose dependent increase in cell injury and ATP media concentrations; 2) enzymatic depletion of extracellular ATP reduces the probability of stretch induced wound repair; 3) enriching extracellular ATP concentrations facilitates wound repair; 4) purinergic effects on cell repair are mediated by ATP and not by one of its metabolites; and 5) ATP mediated cell salvage depends at least in part on P2Y2-R activation. While rescuing cells from wounding induced death may seem appealing, it is possible that survivors of membrane wounding become governors of a sustained pro-inflammatory state and thereby perpetuate and worsen organ function in the early stages of lung injury syndromes. Means to uncouple P2Y2-R mediated cytoprotection from P2Y2-R mediated inflammation and to test the preclinical efficacy of such an undertaking deserve to be explored.

Participation of the oviductal s100 calcium binding protein G in the genomic effect of estradiol that accelerates oviductal embryo transport in mated rats

BACKGROUND

Mating changes the mechanism by which E2 regulates oviductal egg transport, from a non-genomic to a genomic mode. Previously, we found that E2 increased the expression of several genes in the oviduct of mated rats, but not in unmated rats. Among the transcripts that increased its level by E2 only in mated rats was the one coding for an s100 calcium binding protein G (s100 g) whose functional role in the oviduct is unknown.

METHODS

Herein, we investigated the participation of s100 g on the E2 genomic effect that accelerates oviductal transport in mated rats. Thus, we determined the effect of E2 on the mRNA and protein level of s100 g in the oviduct of mated and unmated rats. Then, we explored the effect of E2 on egg transport in unmated and mated rats under conditions in which s100 g protein was knockdown in the oviduct by a morpholino oligonucleotide against s100 g (s100 g-MO). In addition, the localization of s100 g in the oviduct of mated and unmated rats following treatment with E2 was also examined.

RESULTS

Expression of s100 g mRNA progressively increased at 3-24 h after E2 treatment in the oviduct of mated rats while in unmated rats s100 g increased only at 12 and 24 hours. Oviductal s100 g protein increased 6 h following E2 and continued elevated at 12 and 24 h in mated rats, whereas in unmated rats s100 g protein increased at the same time points as its transcript. Administration of a morpholino oligonucleotide against s100 g transcript blocked the effect of E2 on egg transport in mated, but not in unmated rats. Finally, immunoreactivity of s100 g was observed only in epithelial cells of the oviducts of mated and unmated rats and it was unchanged after E2 treatment.

CONCLUSIONS

Mating affects the kinetic of E2-induced expression of s100 g although it not changed the cellular localization of s100 g in the oviduct after E2 . On the other hand, s100 g is a functional component of E2 genomic effect that accelerates egg transport. These findings show a physiological involvement of s100 g in the rat oviduct.

A non-genomic signaling pathway shut down by mating changes the estradiol-induced gene expression profile in the rat oviduct

Estradiol (E(2)) accelerates oviductal egg transport through intraoviductal non-genomic pathways in unmated rats and through genomic pathways in mated rats. This shift in pathways has been designated as intracellular path shifting (IPS), and represents a novel and hitherto unrecognized effect of mating on the female reproductive tract. We had reported previously that IPS involves shutting down the E(2) non-genomic pathway up- and downstream of 2-methoxyestradiol. Here, we evaluated whether IPS involves changes in the genomic pathway too. Using microarray analysis, we found that a common group of genes changed its expression in response to E(2) in unmated and mated rats, indicating that an E(2) genomic signaling pathway is present before and after mating; however, a group of genes decreased its expression only in mated rats and another group of genes increased its expression only in unmated rats. We evaluated the possibility that this difference is a consequence of an E(2) non-genomic signaling pathway present in unmated rats, but not in mated rats. Mating shuts down this E(2) non-genomic signaling pathway up- and downstream of cAMP production. The Star level is increased by E(2) in unmated rats, but not in mated rats. This is blocked by the antagonist of estrogen receptor ICI 182 780, the adenylyl cyclase inhibitor SQ 22536, and the catechol-O-methyltransferase inhibitor, OR 486. These results indicate that the E(2)-induced gene expression profile in the rat oviduct differs before and after mating, and this difference is probably mediated by an E(2) non-genomic signaling pathway operating on gene expression only in unmated rats.

Mating changes the subcellular distribution and the functionality of estrogen receptors in the rat oviduct

BACKGROUND

Mating changes the mode of action of 17beta-estradiol (E2) to accelerate oviductal egg transport from a nongenomic to a genomic mode, although in both pathways estrogen receptors (ER) are required. This change was designated as intracellular path shifting (IPS).

METHODS

Herein, we examined the subcellular distribution of ESR1 and ESR2 (formerly known as ER-alpha and ER-beta) in oviductal epithelial cells of rats on day 1 of cycle (C1) or pregnancy (P1) using immunoelectron microscopy for ESR1 and ESR2. The effect of mating on intraoviductal ESR1 or ESR2 signaling was then explored comparing the expression of E2-target genes c-fos, brain creatine kinase (Ckb) and calbindin 9 kDa (s100g) in rats on C1 or P1 treated with selective agonists for ESR1 (PPT) or ESR2 (DPN). The effect of ER agonists on egg transport was also evaluated on C1 or P1 rats.

RESULTS

Receptor immunoreactivity was associated with the nucleus, cytoplasm and plasma membrane of the epithelial cells. Mating affected the subcellular distribution of both receptors as well as the response to E2. In C1 and P1 rats, PPT increased Ckb while both agonists increased c-fos. DPN increased Ckb and s100g only in C1 and P1 rats, respectively. PPT accelerated egg transport in both groups and DPN accelerated egg transport only in C1 rats.

CONCLUSION

Estrogen receptors present a subcellular distribution compatible with E2 genomic and nongenomic signaling in the oviductal epithelial cells of C1 and P1 although IPS occurs independently of changes in the distribution of ESR1 and ESR2 in the oviductal epithelial cells. Mating affected intraoviductal ER-signaling and induced loss of functional involvement of ESR2 on E2-induced accelerated egg transport. These findings reveal a profound influence on the ER signaling pathways exerted by mating in the oviduct.

Genomic priming of the antisecretory response to estrogen in rat distal colon throughout the estrous cycle

The secretion of Cl(-) across distal colonic crypt cells provides the driving force for the movement of fluid into the luminal space. 17beta-Estradiol (E2) produces a rapid and sustained reduction in secretion in females, which is dependent on the novel protein kinase C delta (PKC delta) isozyme and PKA isoform I targeting of KCNQ1 channels. This sexual dimorphism in the E2 response is associated with a higher expression level of PKC delta in female compared with the male tissue. The present study revealed the antisecretory response is regulated throughout the female reproductive (estrous) cycle and is primed by genomic regulation of the kinases. E2 (1-10 nm) decreased cAMP-dependent secretion in colonic epithelia during the estrus, metestrus, and diestrus stages. A weak inhibition of secretion was demonstrated in the proestrus stage. The expression levels of PKC delta and PKA fluctuated throughout the estrous cycle and correlated with the potency of the antisecretory effect of E2. The expression of PKC delta and PKA were up-regulated by estrogen at a transcriptional level via a PKC delta-MAPK-cAMP response element-binding protein-regulated pathway indicating a genomic priming of the antisecretory response. PK Cdelta was activated by the membrane-impermeant E2-BSA, and this response was inhibited by the estrogen receptor antagonist ICI 182,780. The 66-kDa estrogen receptor-alpha isoform was present at the plasma membrane of female colonic crypt cells with a lower abundance found in male colonic crypts. The study demonstrates estrogen regulation of intestinal secretion both at a rapid and transcriptional level, demonstrating an interdependent relationship between both nongenomic and genomic hormone responses.

Catechol-O-Methyltransferase and Methoxyestradiols Participate in the Intraoviductal Nongenomic Pathway Through Which Estradiol Accelerates Egg Transport in Cycling Rats1

Estradiol (E(2)) accelerates oviductal egg transport through intraoviductal nongenomic pathways in cyclic rats and through genomic pathways in pregnant rats. This shift in pathways, which we have provisionally designated as intracellular path shifting (IPS), is caused by mating-associated signals and represents a novel and hitherto unrecognized phenomenon. The mechanism underlying IPS is currently under investigation. Using microarray analysis, we identified several genes the expression levels of which changed in the rat oviduct within 6 hours of mating. Among these genes, the mRNA level for the enzyme catechol-O-methyltransferase (COMT), which produces methoxyestradiols from hydroxyestradiols, decreased 6-fold, as confirmed by real-time PCR. O-methylation of 2-hydroxyestradiol was up to 4-fold higher in oviductal protein extracts from cyclic rats than from pregnant rats and was blocked by OR486, which is a selective inhibitor of COMT. The levels in the rat oviduct of mRNA and protein for cytochrome P450 isoforms 1A1 and 1B1, which form hydroxyestradiols, were detected by RT-PCR and Western blotting. We explored whether methoxyestradiols participate in the pathways involved in E(2)-accelerated egg transport. Intrabursal application of OR486 prevented E(2) from accelerating egg transport in cyclic rats but not in pregnant rats, whereas 2-methoxyestradiol (2ME) and 4-methoxyestradiol mimicked the effect of E(2) on egg transport in cyclic rats but not in pregnant rats. The effect of 2ME on egg transport was blocked by intrabursal administration of the protein kinase inhibitor H-89 or the antiestrogen ICI 182780, but not by actinomycin D or OR486. We conclude that in the absence of mating, COMT-mediated formation of methoxyestradiols in the oviduct is essential for the nongenomic pathway through which E(2) accelerates egg transport in the rat oviduct. Yet unidentified mating-associated signals, which act directly on oviductal cells, shut down the E(2) nongenomic signaling pathway upstream and downstream of methoxyestradiols. These findings highlight a physiological role for methoxyestradiols in the female genital tract, thereby confirming the occurrence of and providing a partial explanation for the mechanism underlying IPS.