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Relationship: 2580


The title of the KER should clearly define the two KEs being considered and the sequential relationship between them (i.e., which is upstream and which is downstream). Consequently all KER titles take the form “upstream KE leads to downstream KE”.  More help

Suppression, Estrogen receptor (ER) activity leads to Increased, secretion of GnRH from hypothalamus

Upstream event
Upstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help
Downstream event
Downstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes. Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

This table is automatically generated upon addition of a KER to an AOP. All of the AOPs that are linked to this KER will automatically be listed in this subsection. Clicking on the name of the AOP in the table will bring you to the individual page for that AOP. More help
AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Hypothalamic estrogen receptors inhibition leading to ovarian cancer adjacent High Not Specified Cataia Ives (send email) Under development: Not open for comment. Do not cite

Taxonomic Applicability

Select one or more structured terms that help to define the biological applicability domain of the KER. In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. Authors can indicate the relevant taxa for this KER in this subsection. The process is similar to what is described for KEs (see pages 30-31 and 37-38 of User Handbook) More help
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
rat Rattus norvegicus High NCBI
mice Mus sp. High NCBI

Sex Applicability

Authors can indicate the relevant sex for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of the User Handbook). More help
Sex Evidence
Female High
Male Low

Life Stage Applicability

Authors can indicate the relevant life stage for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of User Handbook). More help
Term Evidence
Adult, reproductively mature High

Key Event Relationship Description

Provide a brief, descriptive summation of the KER. While the title itself is fairly descriptive, this section can provide details that aren’t inherent in the description of the KEs themselves (see page 39 of the User Handbook). This description section can be viewed as providing the increased specificity in the nature of upstream perturbation (KEupstream) that leads to a particular downstream perturbation (KEdownstream), while allowing the KE descriptions to remain generalised so they can be linked to different AOPs. The description is also intended to provide a concise overview for readers who may want a brief summation, without needing to read through the detailed support for the relationship (covered below). Careful attention should be taken to avoid reference to other KEs that are not part of this KER, other KERs or other AOPs. This will ensure that the KER is modular and can be used by other AOPs. More help

Study on female human patient had shown Selective Estrogen Receptors Modulator (Clomiphene) act on the hypothalamic site and increase the hypothalamic GnRH secretion significantly (KERIN et al., 1985). Study on female rat had shown increased gonadotropin hormone secretion upon administration of very low dose (1-100 ng/kg) of clomiphene citrate. However, high dose (1µg/kg -2 mg/kg) of clomiphene citrate in female rat inhibit the gonadotropin hormone secretion (Koch et al., 1971).

Estradiol i.e. Estrogen receptor beta acts as a potent feedback molecule between the ovary and hypothalamic GnRH neurons, and exerts both positive and negative regulatory actions on GnRH synthesis and secretion (Hu et al., 2008). ESR2 control the GnRH release through the intracellular calcium ions release (Kenealy et al., 2011). Research had shown that nanomolar concentration of membrane-associated G protein-coupled estrogen receptor alter the patterns of Ca2+ release in GnRH neurone (Komatsuzaki and Kawato, 2007). Studies on mouse have shown several molecules such as, eastradiol, non-peptide neurotransmitters, gasotransmitters can modulate the GnRH neuron activity and GnRH secretion and control the reproductive functions (Spergel, 2019; Temple et al., 2004; Temple and Wray, 2005).

Evidence Supporting this KER

Assembly and description of the scientific evidence supporting KERs in an AOP is an important step in the AOP development process that sets the stage for overall assessment of the AOP (see pages 49-56 of the User Handbook). To do this, biological plausibility, empirical support, and the current quantitative understanding of the KER are evaluated with regard to the predictive relationships/associations between defined pairs of KEs as a basis for considering WoE (page 55 of User Handbook). In addition, uncertainties and inconsistencies are considered. More help

Koch et al., had shown the ~107% increase in GnRH secretion after administration of clomiphene citrate (1-100 ng/kg) in adult female rat (Koch et al., 1971).

Boyer et al., had also shown the increasing GnRH secretion after administration of clomiphene citrate (1.0 mg/kg/day)in immature female rats (Boyar, 1970).

Roy et al., had shown that 17β-estradiol at 1 nm concentration over a 48 h time period down regulate (~55%) the expression of GnRH mRNA in GnRH-secreting, hypothalamic cell line (GT1–7) (Roy et al., 1999).

Chu et al., had shown using whole cell electrophysiology of the brain slice in adult female mice 10 picomolar concentration of estradiol reduce the firing of GnRH neurone (Chu et al., 2009).

Biological Plausibility
Define, in free text, the biological rationale for a connection between KEupstream and KEdownstream. What are the structural or functional relationships between the KEs? For example, there is a functional relationship between an enzyme’s activity and the product of a reaction it catalyses. Supporting references should be included. However, it is recognised that there may be cases where the biological relationship between two KEs is very well established, to the extent that it is widely accepted and consistently supported by so much literature that it is unnecessary and impractical to cite the relevant primary literature. Citation of review articles or other secondary sources, like text books, may be reasonable in such cases. The primary intent is to provide scientifically credible support for the structural and/or functional relationship between the pair of KEs if one is known. The description of biological plausibility can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured (see page 40 of the User Handbook for further information).   More help

Molecular mechanism for the enhancement of GnRH by suppression of Estrogen receptor activity is poorly known.

Uncertainties and Inconsistencies
In addition to outlining the evidence supporting a particular linkage, it is also important to identify inconsistencies or uncertainties in the relationship. Additionally, while there are expected patterns of concordance that support a causal linkage between the KEs in the pair, it is also helpful to identify experimental details that may explain apparent deviations from the expected patterns of concordance. Identification of uncertainties and inconsistencies contribute to evaluation of the overall WoE supporting the AOPs that contain a given KER and to the identification of research gaps that warrant investigation (seep pages 41-42 of the User Handbook).Given that AOPs are intended to support regulatory applications, AOP developers should focus on those inconsistencies or gaps that would have a direct bearing or impact on the confidence in the KER and its use as a basis for inference or extrapolation in a regulatory setting. Uncertainties that may be of academic interest but would have little impact on regulatory application don’t need to be described. In general, this section details evidence that may raise questions regarding the overall validity and predictive utility of the KER (including consideration of both biological plausibility and empirical support). It also contributes along with several other elements to the overall evaluation of the WoE for the KER (see Section 4 of the User Handbook).  More help

The release GnRH neurons depends on the concentration of the Selective Estrogen Receptors Modulator compound (Clomiphene). Scientific reports have shown the both stimulatory and inhibitory effects on the GnRH secretion exhibited by the estradiol depending on the concentration of clomiphene molecules and presence of types of receptors (Chu et al., 2009; Micevych and Kelly, 2012; Boyar, 1970).

Response-response Relationship
This subsection should be used to define sources of data that define the response-response relationships between the KEs. In particular, information regarding the general form of the relationship (e.g., linear, exponential, sigmoidal, threshold, etc.) should be captured if possible. If there are specific mathematical functions or computational models relevant to the KER in question that have been defined, those should also be cited and/or described where possible, along with information concerning the approximate range of certainty with which the state of the KEdownstream can be predicted based on the measured state of the KEupstream (i.e., can it be predicted within a factor of two, or within three orders of magnitude?). For example, a regression equation may reasonably describe the response-response relationship between the two KERs, but that relationship may have only been validated/tested in a single species under steady state exposure conditions. Those types of details would be useful to capture.  More help

Not Specified

This sub-section should be used to provide information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). This can be useful information both in terms of modelling the KER, as well as for analyzing the critical or dominant paths through an AOP network (e.g., identification of an AO that could kill an organism in a matter of hours will generally be of higher priority than other potential AOs that take weeks or months to develop). Identification of time-scale can also aid the assessment of temporal concordance. For example, for a KER that operates on a time-scale of days, measurement of both KEs after just hours of exposure in a short-term experiment could lead to incorrect conclusions regarding dose-response or temporal concordance if the time-scale of the upstream to downstream transition was not considered. More help

Neural activity and elevated hormone release are observed for hours in in vivo study (Chu et al., 2009).

Known modulating factors
This sub-section presents information regarding modulating factors/variables known to alter the shape of the response-response function that describes the quantitative relationship between the two KEs (for example, an iodine deficient diet causes a significant increase in the slope of the relationship; a particular genotype doubles the sensitivity of KEdownstream to changes in KEupstream). Information on these known modulating factors should be listed in this subsection, along with relevant information regarding the manner in which the modulating factor can be expected to alter the relationship (if known). Note, this section should focus on those modulating factors for which solid evidence supported by relevant data and literature is available. It should NOT list all possible/plausible modulating factors. In this regard, it is useful to bear in mind that many risk assessments conducted through conventional apical guideline testing-based approaches generally consider few if any modulating factors. More help

GnRH secretion from the neurone can be modulated by prostaglandin, glutamate, ATP, carbon monoxide, nitric oxide, neurotransmitters (norepinephrine, epinephrine, GABA, histamine and acetylcholine) (Spergel, 2019).

Known Feedforward/Feedback loops influencing this KER
This subsection should define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits? In some cases where feedback processes are measurable and causally linked to the outcome, they should be represented as KEs. However, in most cases these features are expected to predominantly influence the shape of the response-response, time-course, behaviours between selected KEs. For example, if a feedback loop acts as compensatory mechanism that aims to restore homeostasis following initial perturbation of a KE, the feedback loop will directly shape the response-response relationship between the KERs. Given interest in formally identifying these positive or negative feedback, it is recommended that a graphical annotation (page 44) indicating a positive or negative feedback loop is involved in a particular upstream to downstream KE transition (KER) be added to the graphical representation, and that details be provided in this subsection of the KER description (see pages 44-45 of the User Handbook).  More help

Not Specified

Domain of Applicability

As for the KEs, there is also a free-text section of the KER description that the developer can use to explain his/her rationale for the structured terms selected with regard to taxonomic, life stage, or sex applicability, or provide a more generalizable or nuanced description of the applicability domain than may be feasible using standardized terms. More help

Negative feedback action on GnRH secretion had shown in female guinea pig (Kelly et al., 1984).

Reduced firing of GnRH neurone was shown in adult female mice (Chu et al., 2009).

Alterations in the concentrations of oestrogen receptors in the hypothalamus was shown in rat (Adashi et al., 1980).

Negative Feedback of estrogen on GnRH secretion was studied in adult woman (Shaw et al., 2010).


List of the literature that was cited for this KER description using the appropriate format. Ideally, the list of references should conform, to the extent possible, with the OECD Style Guide (OECD, 2015). More help

Adashi, E., Hsueh, A., & Yen, S. (1980). Alterations induced by clomiphene in the concentrations of oestrogen receptors in the uterus, pituitary gland and hypothalamus of female rats. Journal of Endocrinology, 87(3), 383-392.

Baez-Jurado, E., Rincon-Benavides, M. A., Hidalgo-Lanussa, O., Guio-Vega, G., Ashraf, G. M., Sahebkar, A., et al. (2018). Molecular mechanisms involved in the protective actions of Selective Estrogen Receptor Modulators in brain cells. Front Neuroendocrinol, 52, 44-64. doi:S0091-3022(18)30094-3 [pii]10.1016/j.yfrne.2018.09.001.

Bharti, S., Misro, M., & Rai, U. (2013). Clomiphene citrate potentiates the adverse effects of estrogen on rat testis and down-regulates the expression of steroidogenic enzyme genes. Fertility and sterility, 99(1), 140-148. e5.

Boyar, R. M. (1970). Effects of clomiphene citrate on pituitary FSH, FSH-RF, and release of LH in immature and mature rats. Endocrinology, 86(3), 629-33. doi:10.1210/endo-86-3-629.

Bussenot, I., Parinaud, J., Clamagirand, C., Vieitez, G., & Pontonnier, G. (1990). Effect of clomiphene cirate on oestrogen secretion by human granulosa cells in culture. Human Reproduction, 5(5), 533-536.

Chu, Z., Andrade, J., Shupnik, M. A., & Moenter, S. M. (2009). Differential regulation of gonadotropin-releasing hormone neuron activity and membrane properties by acutely applied estradiol: dependence on dose and estrogen receptor subtype. J Neurosci, 29(17), 5616-27. doi:29/17/5616 [pii]10.1523/JNEUROSCI.0352-09.2009.

Cosman, F. (2003). Selective estrogen-receptor modulators. Clin Geriatr Med, 19(2), 371-9. doi:S0749-0690(02)00114-3 [pii]10.1016/s0749-0690(02)00114-3.

Couse, J. F., & Korach, K. S. (1999). Estrogen receptor null mice: what have we learned and where will they lead us? Endocr Rev, 20(3), 358-417. doi:10.1210/edrv.20.3.0370.

Goerzen, J., Corenblum, B., & Taylor, P. J. (1985). Potentiation of GnRH response by clomiphene citrate. J Reprod Med, 30(10), 749-52.

Haskell, S. G. (2003). Selective estrogen receptor modulators. South Med J, 96(5), 469-76. doi:10.1097/01.SMJ.0000051146.93190.4A.

Hu, L., Gustofson, R. L., Feng, H., Ki Leung, P., Mores, N., Krsmanovic, L. Z., et al. (2008). Converse regulatory functions of estrogen receptor-α and-β subtypes expressed in hypothalamic gonadotropin-releasing hormone neurons. Molecular Endocrinology, 22(10), 2250-2259.

Kelly, M. J., Ronnekleiv, O. K., & Eskay, R. L. (1984). Identification of estrogen-responsive LHRH neurons in the guinea pig hypothalamus. Brain Res Bull, 12(4), 399-407. doi:0361-9230(84)90112-6 [pii]10.1016/0361-9230(84)90112-6.

Kenealy, B., Keen, K., & Terasawa, E. (2011). Rapid action of estradiol in primate GnRH neurons: the role of estrogen receptor alpha and estrogen receptor beta. Steroids, 76(9), 861-866.

KERIN, J. F., LIU, J. H., PHILLIPOU, G., & Yen, S. (1985). Evidence for a hypothalamic site of action of clomiphene citrate in women. The Journal of Clinical Endocrinology & Metabolism, 61(2), 265-268.

Koch, Y., Dikstein, S., Superstine, E., & Sulman, F. G. (1971). The effect of promethazine and clomiphene on gonadotrophin secretion in the rat. J Endocrinol, 49(1), 13-7. doi:10.1677/joe.0.0490013.

Komatsuzaki, Y., & Kawato, S. (2007). Rapid Effect of Progesterone on the Intracellular Ca2+ Oscillation of Immortalized Hypothalamic GT1-7 Cells. bioimages, 15, 1-7.

Kumar, A., & Pakrasi, P. L. (1995). Estrogenic and antiestrogenic properties of clomiphene citrate in laboratory mice. Journal of Biosciences, 20(5), 665-673.

Micevych, P. E., & Kelly, M. J. (2012). Membrane estrogen receptor regulation of hypothalamic function. Neuroendocrinology, 96(2), 103-10. doi:000338400 [pii]10.1159/000338400.

Ng, Y., Wolfe, A., Novaira, H. J., & Radovick, S. (2009). Estrogen regulation of gene expression in GnRH neurons. Molecular and cellular endocrinology, 303(1-2), 25-33.

Petersen, S. L., McCrone, S., Keller, M., & Shores, S. (1995). Effects of estrogen and progesterone on luteinizing hormone-releasing hormone messenger ribonucleic acid levels: consideration of temporal and neuroanatomical variables. Endocrinology, 136(8), 3604-10. doi:10.1210/endo.136.8.7628399.

Roy, D., Angelini, N. L., & Belsham, D. D. (1999). Estrogen directly represses gonadotropin-releasing hormone (GnRH) gene expression in estrogen receptor-α (ERα)-and ERβ-expressing GT1–7 GnRH neurons. Endocrinology, 140(11), 5045-5053.

Shaw, N. D., Histed, S. N., Srouji, S. S., Yang, J., Lee, H., & Hall, J. E. (2010). Estrogen negative feedback on gonadotropin secretion: evidence for a direct pituitary effect in women. J Clin Endocrinol Metab, 95(4), 1955-61. doi:jc.2009-2108 [pii]10.1210/jc.2009-2108.

Spergel, D. J. (2019). Modulation of Gonadotropin-Releasing Hormone Neuron Activity and Secretion in Mice by Non-peptide Neurotransmitters, Gasotransmitters, and Gliotransmitters. Front Endocrinol (Lausanne), 10, 329. doi:10.3389/fendo.2019.00329.

Tan, S. L., Farhi, J., Homburg, R., & Jacobs, H. S. (1996). Induction of ovulation in clomiphene-resistant polycystic ovary syndrome with pulsatile GnRH. Obstet Gynecol, 88(2), 221-6. doi:0029-7844(96)00190-1 [pii]10.1016/0029-7844(96)00190-1.

Temple, J. L., Laing, E., Sunder, A., & Wray, S. (2004). Direct action of estradiol on gonadotropin-releasing hormone-1 neuronal activity via a transcription-dependent mechanism. J Neurosci, 24(28), 6326-33. doi:10.1523/JNEUROSCI.1006-04.200424/28/6326 [pii].

Temple, J. L., & Wray, S. (2005). Bovine serum albumin-estrogen compounds differentially alter gonadotropin-releasing hormone-1 neuronal activity. Endocrinology, 146(2), 558-63. doi:en.2004-1117 [pii]10.1210/en.2004-1117.

Zhang, Z., Bartsch, J. W., Benzel, J., Lei, T., Nimsky, C., & Voellger, B. (2009). Selective estrogen receptor modulators decrease invasiveness in pituitary adenoma cell lines AtT-20 and TtT/GF by affecting expression of MMP-14 and ADAM12. FEBS Open Bio, 10(11), 2489-2498. doi:10.1002/2211-5463.12999.

Zoeller, R. T., & Young, W. S., 3rd (1988). Changes in cellular levels of messenger ribonucleic acid encoding gonadotropin-releasing hormone in the anterior hypothalamus of female rats during the estrous cycle. Endocrinology, 123(3), 1688-9. doi:10.1210/endo-123-3-1688.