1. Foundations: Understanding Menopause
Pedagogy: This lesson uses mechanistic illustration and translational reasoning — connecting basic neuroscience (KNDy pathway) to clinical therapeutics (fezolinetant), building the "why" behind treatment choices.
Learning Objectives
- Explain the hormonal changes of the menopausal transition, including the roles of oestradiol, FSH, inhibin B, and AMH.
- Describe the shift from an oestrogenic to a relatively androgenic endocrine milieu and its metabolic consequences.
- Illustrate the KNDy neuron pathway and explain how oestrogen withdrawal causes vasomotor symptoms.
- Relate thermoregulatory narrowing of the thermoneutral zone to hot flushes and the mechanism of NK3 receptor antagonists.
Key Facts
The HPO Axis in Decline
The menopausal transition is driven by progressive depletion of ovarian follicles and consequent decline in ovarian hormone production. As the follicular pool diminishes, inhibin B secretion falls, releasing the anterior pituitary from negative feedback. FSH rises as a result. Oestradiol production becomes erratic during perimenopause before declining to permanently low postmenopausal levels (1,2).
Anti-Müllerian hormone (AMH) declines progressively throughout reproductive life and becomes undetectable at menopause. AMH is the earliest biochemical marker of declining ovarian reserve, although it is not recommended for diagnosing menopause in routine practice (1).
The Oestrogenic-to-Androgenic Shift
As oestradiol falls, the endocrine milieu shifts from predominantly oestrogenic to relatively androgenic. SHBG concentrations decline, increasing bioavailable testosterone. This explains key clinical features of the transition (2,3):
| Hormonal Change | Clinical Consequence |
|---|---|
| ↓ Oestradiol | VMS, vaginal atrophy, accelerated bone loss, adverse lipid changes, mood disturbance |
| ↑ FSH | Marker of ovarian failure; diagnostic in women <45 years |
| ↓ Inhibin B | Loss of pituitary negative feedback; drives FSH rise |
| ↓ AMH | Reflects follicular depletion; earliest marker of declining ovarian reserve |
| ↓ SHBG / relative ↑ testosterone | Centripetal fat redistribution, visceral adiposity, metabolic syndrome risk |
The KNDy Neuron Pathway
KNDy neurons in the hypothalamic arcuate (infundibular) nucleus co-express three neuropeptides: kisspeptin, neurokinin B (NKB), and dynorphin. Before menopause, oestrogen exerts tonic inhibition on KNDy neurons. With menopausal oestrogen withdrawal (1,2):
→ KNDy neurons hypertrophy
→ Kisspeptin and NKB gene expression increases; dynorphin expression declines
→ Net increase in NKB release
→ NKB neurons project onto thermoregulatory neurons in the median preoptic area
→ Inappropriate peripheral vasodilation and sweating = hot flush
The thermoneutral zone narrows significantly, meaning minor core temperature fluctuations now cross the threshold for heat dissipation. This mechanism is the direct target of NK3 receptor antagonist therapies such as fezolinetant (2).
Clinical Pearl
The KNDy pathway explains WHY oestrogen withdrawal causes hot flushes and WHY NK3 receptor antagonists work without hormones. Understanding this pathway is essential for explaining non-hormonal treatment options to patients — particularly those with breast cancer.
Clinical Pearl
The shift to a relatively androgenic milieu with declining SHBG explains centripetal fat redistribution and metabolic syndrome risk at menopause — independent of chronological ageing (Ravindran & Varma, 2026).
Case-Based Examples
Case 1: "Why do I keep getting these hot flushes?"
Presentation: A 50-year-old reports hot flushes every 2–3 hours, drenching night sweats, and 8 kg abdominal weight gain over 2 years. She asks why this is happening.
Question: Explain the pathophysiological basis in patient-friendly terms.
Model Answer: Her flushes result from oestrogen withdrawal affecting the brain's thermostat. Oestrogen normally keeps temperature-regulating neurons (KNDy neurons) in check. As oestrogen falls, these neurons overreact and trigger cooling — vasodilation and sweating — even when core temperature barely changes. Her central weight gain reflects the hormonal shift: declining oestrogen and SHBG increase androgens' influence, promoting visceral fat. IMS 2025: midlife weight gain is mostly ageing-related, but abdominal redistribution is menopause-specific.
Case 2: Breast cancer patient asking about "that new non-hormonal tablet"
Presentation: A 47-year-old with HR+ breast cancer on tamoxifen develops severe VMS (12–15/day) following chemotherapy-induced ovarian suppression. MHT is contraindicated.
Question: Explain fezolinetant's mechanism and its relevance to this patient.
Model Answer: Fezolinetant is a selective NK3 receptor antagonist. It blocks NKB signalling at the hypothalamic thermoregulatory centre, suppressing the overactive KNDy pathway without oestrogenic stimulus — mechanistically suitable for oestrogen-sensitive cancers. The DAYLIGHT trial demonstrated significant VMS reductions at 24 weeks in women unsuitable for MHT. NICE TA1143 (2026) recommends fezolinetant for moderate-to-severe VMS when HRT is unsuitable. Note: avoid paroxetine with tamoxifen (CYP2D6 inhibition). Elinzanetant (dual NK1/NK3) has also shown efficacy for endocrine therapy-associated VMS.
Self-Assessment Questions
PLAB/MLA Neuropeptide pathway responsible for VMS
Which neuropeptide pathway is primarily responsible for generating vasomotor symptoms in menopausal women?
A. Serotonin–noradrenaline pathway in dorsal raphe nucleus
B. Kisspeptin–neurokinin B–dynorphin (KNDy) pathway in hypothalamic arcuate nucleus
C. Dopamine pathway in tuberoinfundibular tract
D. GABA-ergic pathway in preoptic area
E. CRH pathway in paraventricular nucleus
Answer: B. KNDy neurons in the arcuate nucleus co-express kisspeptin, NKB, and dynorphin. Oestrogen withdrawal leads to hypertrophy and increased NKB release, which projects onto thermoregulatory neurons in the preoptic area, generating VMS.
MRCGP Counselling about cardiometabolic changes and HRT for CVD
A 51-year-old asks: "I've read menopause causes heart disease. Should I be on HRT to protect my heart?"
Outline how you would explain the cardiometabolic changes and the role of HRT in CVD prevention.
Model Answer: Explain the hormonal shift — falling oestradiol, declining SHBG, relative androgen excess — causes real biological changes: rising LDL, visceral adiposity, insulin resistance, BP elevation. These increase CVD risk. However, NICE NG23 (2024) states HRT should NOT be offered for primary or secondary CVD prevention. The "window of opportunity" hypothesis is not supported by statistically significant RCT subgroup differences. Instead: use the menopause consultation for QRISK3, fasting lipids, HbA1c, BP. Prescribe HRT for symptom relief. Address CVD risk with statins, antihypertensives, and lifestyle modification. This is the precision menopause approach.
Professor Translational pathway from KNDy discovery to NK3R antagonists
Discuss the translational pathway from basic neuroscience discovery to the development of NK3 receptor antagonists, evaluating evidence quality at each stage.
Model Answer: Post-mortem studies → KNDy neuron hypertrophy in postmenopausal women (Rometo & Rance, 2008). NKB infusion studies → exogenous NKB triggers flushes in premenopausal women (Jayasena et al., 2015; Level 2b). Phase 2 RCT of MLE4901 (Prague et al., Lancet 2017) → significant VMS reduction but liver safety concerns. Fezolinetant → Phase 2 dose-finding (Fraser et al., 2020), Phase 3 SKYLIGHT trials, Phase 3b DAYLIGHT trial (Schaudig et al., BMJ 2024). Limitations: relatively short trial durations (24–52 weeks); exclusion of significant hepatic impairment; need for long-term safety data beyond 2 years. Elinzanetant (dual NK1/NK3) → second-generation approach with potential additional sleep/mood benefits via NK1 blockade.
Take-Away Messages
- Follicular depletion → ↓ inhibin B → ↑ FSH → ↓ oestradiol drives the menopausal transition.
- The endocrine milieu shifts from oestrogenic to androgenic, explaining centripetal fat redistribution and metabolic syndrome risk.
- KNDy neurons (kisspeptin/NKB/dynorphin) in the arcuate nucleus mediate VMS via projections to the thermoregulatory centre.
- Oestrogen withdrawal causes KNDy hypertrophy and thermoneutral zone narrowing.
- NK3 receptor antagonists (fezolinetant) block this pathway without hormonal activity — a paradigm shift for non-hormonal treatment.
References
- Lumsden MA, et al. ESE Clinical Practice Guideline: menopause and perimenopause. Eur J Endocrinol. 2025;193(4):G49–G79. DOI
- Davis SR, et al. Menopausal hormone therapy: beyond the traditional indications. Nat Rev Endocrinol. 2022;18:611–627. DOI
- Ravindran N, Varma R. Cardiometabolic changes at menopause. InnovAiT. 2026. DOI