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Relationship: 3716

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

Increase, Gonadotropins concentration in plasma leads to Increased, E2 production in ovaries

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Increase, Gonadotropins concentration in plasma
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help
Increased, E2 production in ovaries

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 Do not cite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
Female 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

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 gonadotropins of particular interest because of roles in the hypothalamus- pituitary-gonadal (HPG) axis, and are released from the anterior pituitary gland (Howard 2021), resulting in increased production of estradiol in the ovaries.  

Production of estradiol (E2) by the ovaries has been well-established by the two-cell, two gonadotropin model of steroid biosynthesis (for review see Drummond 2006; Kimura et al. 2007; Palermo 2007; Beevors et al. 2024). Luteinizing hormone stimulates steroid production in theca cells, with follicle-stimulating hormone stimulates steroid production in granulosa cells.

Table 1: List of steroid synthesis enzymes with identifier of enzyme (Uniprot, 2025).

Enzyme

Identifier

Steroidogenic acute regulatory protein, mitochondrial (STAR)

 

Cholesterol side-chain cleavage enzyme, mitochondrial (CYP11A)

EC:1.14.15.6

3 beta-hydroxysteroid dehydrogenase (3B-HSD)

EC:1.1.1.145

Steroid 17-alpha-hydroxylase (CYP17A1)

EC:1.14.14.19

17-beta-hydroxysteroid dehydrogenase (17B-HSD)

EC:1.1.1.105

Aromatase (CYP19A1)

EC:1.14.14.14

3-oxo-5-alpha-steroid 4-dehydrogenase 2 (SRD5A2)

EC:1.3.1.22

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 fast Luteinizing hormone/ Follicle-stimulating hormone (LH/FSH) pulsatile release and resulting increased estradiol production in ovaries, in support of development of AOP 623.

Authors of KER 3716 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 ‘Luteinizing hormone,’ ‘Follicle-stimulating hormone,’ and ‘Estradiol’ 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 Luteinizing hormone/ Follicle-stimulating hormone (LH/FSH) levels and resulting increased estradiol production in ovaries have been studied in laboratory mammals by addition of hormones (Sashida and Johnson 1976; Spears et al. 1998; Murray et al. 2008).  In vitro studies isolating ovarian follicles have been useful in isolating the essentiality of gonadotropins by selective addition (Spears et al. 1998; Murray et al. 2008).  Luteinizing hormone binds to receptors on the surface of theca cells, while follicle-stimulating hormone binds to receptors on granulosa cells, cueing cyclic adenosine monophosphate (cAMP) signalling cascades in each cell that results in increased production of enzymes needed for conversion of cholesterol precursor to steroid compounds.  Theca cells and granulosa cells are responsible for different enzyme-catalyzed reaction steps resulting in the generation of estradiol.

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
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 females as specific to ovaries.

Taxonomic: Primarily studied in humans and laboratory rodents.  Plausible for most mammals due to conserved hormone pathways regulating hypothalamus-pituitary-gonadal axis processes.  Gonadotropins and estradiol production in ovaries widespread among vertebrates, including fish, amphibians, reptiles, birds, and mammals (Bondesson et al. 2015; Li et al. 2019; Hollander-Cohen et al. 2021; Hanlon et al. 2022; Cruz-Cano et al. 2023).  

References

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

Beevors LI, Sundar S, Foster PA. 2024. Steroid metabolism and hormonal dynamics in normal and malignant ovaries. Essays in Biochemistry 68(4): 491-507.

Bondesson M, Hao R, Lin CY, Williams C, Gustafsson JA. 2015.  Estrogen receptor signaling during vertebrate development. Biochimica et Biophysica Acta 1849(2): 142-151. 

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.

Cruz-Cano NB, Sanchez-Rivera UA, Alvarez-Rodriguez C, Cardenas-Leon M, Martinez-Torres M. 2023.  Sex steroid receptors in the ovarian follicles of the lizard Sceloporus torquatus. Zygote. 31(4): 386-392.

Drummond AE. 2006.  The role of steroids in follicular growth. Reproductive Biology and Endocrinology 4:16. 

Hanlon C, Ziezold CJ, Bedecarrats GY. 2022.  The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens. Frontiers in Physiology 13: 942790. 

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.

Kimura S, Matsumoto T, Matsuyama R, Shiina H, Sato T, Takeyama K, Kato S. 2007. Androgen receptor function in folliculogenesis and its clinical implication in premature ovarian failure. Trends in Endocrinology and Metabolism 18(5): 183-189.

Li M, Sun L, Wang D. 2019.  Roles of estrogens in fish sexual plasticity and sex differentiation. General and Comparative Endocrinology 277: 9-16.

Murray AA, Swales AK, Smith RE, Molinek MD, Hillier SG, Spears N.  2008.  Follicular growth and oocyte competence in the in vitro cultured mouse follicle: effects of gonadotrophins and steroids. MHR-Basic Science of Reproductive Medicine 14(2): 75-83.

Palermo R. 2007. Differential actions of FSH and LH during folliculogenesis. Reproductive BioMedicine Online 15(3): 326-337. 

Sashida T, Johnson DC. 1976.  Stimulation of the estrogen synthesizing system of the immature rat ovary by exogenous and endogenous gonadotropins. Steroids 27(4): 469-79. 

Spears N, Murray AA, Allison V, Boland NI, Gosden RG. 1998.  Role of gonadotrophins and ovarian steroids in the development of mouse follicles in vitro. Journal of Reproduction and Fertility 113(1): 19-26.

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).

The UniProt Consortium.  UniProt: the Universal Protein Knowledgebase in 2025. https://www.uniprot.org/ (retrieved 2 November 2025).

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.