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Relationship: 3715

Title

A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

Increased, secretion of GnRH from hypothalamus leads to Increase, Gonadotropins concentration in plasma

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

Increased, secretion of GnRH from hypothalamus

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

Increase, Gonadotropins concentration in plasma

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

AOP Name	Adjacency	Weight of Evidence	Quantitative Understanding	Point of Contact	Author Status	OECD Status
Activation, estrogen receptor alpha leads to persistent vaginal cornification via increased kisspeptin release	adjacent	High		John Frisch (send email)	Under development: Not open for comment. Do not cite

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) 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. More help

Term	Scientific Term	Evidence	Link
mammals	mammals	Moderate	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Unspecific	High

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Adult, reproductively mature	Moderate
Juvenile	Moderate

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help

Gonadotropin-releasing hormone (GnRH) is produced by the hypothalamus. Gonadotropin-releasing hormone is a peptide hormone composed of 10 amino acids (Hassanein et al. 2024). Increases in GnRH stimulate increased production of Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH), two types of gonadotropins. GnRH activation of gonadotropin production is triggered via a G-protein, phospholipase C activation, and mitogen-activated protein kinase (MAPK) pathway activation (Hassanein et al. 2024). LH and FSH are important hormones in the hypothalamus- pituitary-gonadal (HPG) axis. Increased GnRH release leads to increased production of gonadotropins in the anterior pituitary gland.

Gonadotropins are hormones in mammals that cue development of reproductive organs to maturity (Casarini and Simoni 2021; Howard 2021) and the different phases of the estrus cycle (Uenoyama et al. 2021). Gonadotropins are composed of two subunits: a 90-100 amino acid alpha subunit that is identical for all gonadotropins for a species, and a 105-150 amino acid beta subunit that are unique to each gonadotropin but exhibit large similarities in order to interact with alpha subunits (Cahoreau et al 2015). Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) are released from the anterior pituitary gland (Howard 2021).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings. Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

This Key Event Relationship was part of an Environmental Protection Agency effort to develop AOPs that establish scientifically supported causal linkages between alternative endpoints measured using new approach methodologies (NAMs) and guideline apical endpoints measured in Tier 1 and Tier 2 test guidelines (U.S. EPA, 2024) employed by the Endocrine Disruptor Screening Program (EDSP). A series of key events that represent significant, measurable, milestones connecting molecular initiation to apical endpoints indicative of adversity were identified based on scientific review articles and empirical studies. Additionally, scientific evidence supporting the causal relationships between each pair of key events was assembled and evaluated. The present effort focused primarily on empirical studies with laboratory rodents and other mammals.

Empirical studies are focused on increased Gonadotropin-Releasing Hormone (GnRH) and resulting increased gonadotropins in plasma, in support of development of AOP 623.

Authors of KER 3715 did a further evaluation of published peer-reviewed literature to provide additional evidence in support of the key event relationship. The literature used to support this KER began with the test guidelines and followed to primary, secondary, and/or tertiary works concerning the relevant underlying biology. In addition, search engines were used to target journal articles with terms ‘Gonadotropin-releasing hormone,’ ‘Luteinizing hormone,’ and ‘Follicle-stimulating hormone’ to locate representative empirical studies that support the key event relationship.

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field 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. More help

Increased Gonadotropin-Releasing Hormone (GnRH) and resulting increased gonadotropins, with focus on Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH), have been studied in laboratory mammals by addition of estrogen compounds (Clarkson et al. 2008), toxicants (Wang et al. 2014), and modifying diet (Bo et al. 2022). Gene-knock out studies have been useful in showing the essentiality of GnRH in reproductive development and puberty, with GnRH-null animals failing to increase gonadotropin levels (Clarkson et al. 2008). GnRH binds to GnRH receptors on the surface of pituitary gonadotroph cells, triggering gonadotropin production by G-protein, phospholipase C activation, and mitogen-activated protein kinase (MAPK) pathway activation. Fast GnRH pulse secretion cues LH production, and slow GnRH pulse secretion cues FSH production.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Species	Duration	Dose	Increased GnRH?	Increased LH/FSH?	Summary	Citation
Mice (Mus musculus)	1 week	1 ug/20 ug BW 17B-estradiol, ovariectomized.	yes	yes	Female ovariectomized mice exposed to estradiol had statistically significant increased GnRH activity by c-FOS expression (as a molecular marker for GnRH neural activity) leading to statistically significant increased LH hormone levels.	Clarkson et al. (2008)
Mice (Mus musculus)	6 hours	20 ug/kg/bw BPA	yes	yes	Female mice exposed to BPA had statistically significant increased GnRH mRNA at proestrus leading to statistically significant increased LSH and FSH hormone levels at proestrus.	Wang et al. (2014)
Mice (Mus musculus)	14 days	High fat diet	yes	yes	Female mice fed high fat diet had statistically significant increased GnRH protein expression leading to statistically significant increased LH mRNA and increased FSH mRNA.	Bo et al. (2022)
Mice (Mus musculus)	20 days	2 ug/g leptin	yes	yes	Female mice exposed to leptin had statistically significant increases in GnRH mRNA leading to statistically significant increased LSH and FSH hormone levels.	Zhou et al. (2023)

Uncertainties and Inconsistencies

Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references. More help

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Time-scale

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?). More help

Known Feedforward/Feedback loops influencing this KER

Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help

Life Stage: Applies to adult, reproductively mature and juveniles.

Sex: Applies to both males and females as both sexes require signalling for GnRH-gonadotropin signalling for hormone pathways.

Taxonomic: Primarily studied in humans and laboratory rodents. Plausible for most mammals due to conserved hormone pathways regulating hypothalamus-pituitary-gonadal axis processes. GnRH and gonadotropins widespread among vertebrates, including fish, amphibians, reptiles, birds, and mammals (Duan and Allard 2020; Hollander-Cohen et al. 2021).

References

List of the literature that was cited for this KER description. More help

Bo T, Liu M, Tang L, Lv J, Wen J, Wang D. 2022. Effects of High-Fat Diet During Childhood on Precocious Puberty and Gut Microbiota in Mice. Frontiers in Microbiology 13: 930747.

Cahoreau C, Klett D, Combarnous Y. 2015. Structure-function relationships of glycoprotein hormones and their subunits' ancestors. Frontiers in Endocrinology 6: 26. Casarini, L. and Simoni M. 2021. Recent advances in understanding gonadotropin signaling. Faculty Reviews 10: 41.

Clarkson J, d’Anglemont de Tassigny X, Moreno AS, Colledge WH, Herbison AE. 2008. Kisspeptin–GPR54 signaling is essential for preovulatory gonadotropin-releasing hormone neuron activation and the luteinizing hormone surge. Journal of Neuroscience 28(35): 8691–8697.

Duan C, Allard J. 2020. Gonadotropin-releasing hormone neuron development in vertebrates. General and Comparative Endocrinology. 292: 113465.

Hassanein, E.M., Szelényi, Z., Szenci, O. 2024. Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction I: Structure, Biosynthesis, Physiological Effects, and Its Role in Estrous Synchronization. Animals 14: 1473.

Hollander-Cohen L, Golan M, Levavi-Sivan B. 2021. Differential Regulation of Gonadotropins as Revealed by Transcriptomes of Distinct LH and FSH Cells of Fish Pituitary. International Journal of Molecular Sciences 22(12): 6478. Howard, S.R. 2021. Interpretation of reproductive hormones before, during and after the pubertal transition—identifying health and disordered puberty. Clinical Endocrinolology 95: 702-715. Uenoyama, Y., Inoue, N., Nakamura, S., and Tsukamura, H. Kisspeptin Neurons and Estrogen–Estrogen Receptor α Signaling: Unraveling the Mystery of Steroid Feedback System Regulating Mammalian Reproduction. 2021. International Journal of Molecular Sciences 22(17): 9229.

U.S. Environmental Protection Agency. 2004. EDSP Test Guidelines and Guidance Document. https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/edsp-test-guidelines-and-guidance-document (retrieved 25 July 2025).

Wang X, Chang F, Bai Y, Chen F, Zhang J, Chen L. 2014. Bisphenol A enhances kisspeptin neurons in anteroventral periventricular nucleus of female mice. Journal of Endocrinology 28(35): 201-213.

Zhou L, Ren Y, Li D, Zhou W, Li C, Wang Q, Yang X. 2023. Timosaponin AIII attenuates precocious puberty in mice through downregulating the hypothalamic-pituitary-gonadal axis. Acta Biochimica Polonica 70(1): 183-190.

Italics indicate edits from John Frisch February 2026. A full list of updates can be found in the Change Log on the View History page.