Reproductive axis
FSH/LH/HPG axis
Also searched as FSH/LH/HPG axis.
You want it functioning: a well-tuned HPG axis sustains hormones, fertility and vitality.
In depth
The hypothalamic–pituitary–gonadal axis — the command line of sex-hormone production and reproductive health.
What drives it
Stress & cortisol reduces it.
CRF/GnRH review 2010, Brain Res — stress activates the HPA axis and suppresses the HPG axis; CRF is a potent inhibitor of the GnRH pulse generator, reducing LH/FSH. PMID 20727865. Mechanism is specific, not generic 'stress is bad': gonadal function and reproduction are suppressed in response to various stressors by two distinct CRF-mediated routes. (1) pituitary: stress-induced CRF stimulates urocortin-2 production in corticotrophs, which inhibits gonadotropin secretion via the CRF-2 receptor. (2) hypothalamus: CRF suppresses the HPG axis at the GnRH pulse generator itself via hypothalamic CRF receptors. Suppressing the pulse generator matters more than suppressing the hormone, because GnRH must be pulsatile to work. PMID 20727865
Reproductive trigger hormone increases it.
Human genetics is decisive: inactivating mutations of the kisspeptin receptor (GPR54/KISS1R) in humans cause failure to PROGRESS through puberty and adult infertility — hypogonadotropic hypogonadism with capable gonads that are never signaled. Loss of function, pharmacological: the selective antagonist peptide 234 inhibited the post-castration LH rise in mice, blunted the LH response in rats, and suppressed LH pulse frequency and amplitude in ewes and GnRH pulses in monkeys. Gain of function, in humans: 12-hour intravenous Kp-10 in women with cabergoline-resistant hyperprolactinaemic amenorrhoea significantly raised LH and FSH, increased LH pulses, and raised estradiol, testosterone and inhibin B (PMC5686678). Hierarchy: kisspeptin neurons in the arcuate and AVPV nuclei release kisspeptin → KISS1R on GnRH neurons → GnRH into the portal circulation → LH and FSH from the anterior pituitary → gonad. Why the gate must exist at all: GnRH neurons lack estrogen receptor alpha and progesterone receptors, so sex-steroid feedback cannot act on them directly — it is relayed through kisspeptin neurons. kisspeptin is a key integrator, not the sole switch — neurokinin B, dynorphin, leptin and estradiol feedback all converge on the same cells; and it is not a simple booster, since its effect depends on the state of the individual's axis. doi 10.3389/fendo.2022.925206 · PMC5686678
Testosterone reduces it.
NBK526128 — This is the return arm of the axis. Negative feedback is the defining property of the HPG axis: without it, the axis would produce a hormone and never switch itself off. The claim is plain: testosterone from the testes exerts negative feedback effects on FSH and LH production by negatively modulating production of GnRH in the hypothalamus, and testicular steroids have major feedback actions directly at the hypothalamus to inhibit the secretion of GnRH. Steroid hormones have a much greater inhibitory effect on LH production than on FSH.
Estrogen balance reduces it.
The inhibitory effect on gonadotropin secretion is mediated mainly by estradiol from endogenous conversion of testosterone rather than direct androgen action, at least in the pituitary gland. The decisive evidence is a human experiment of nature: basal, GnRH-stimulated and pulsatile evaluation of LH and FSH in two aromatase-deficient men provided direct evidence that circulating estrogens exert an inhibitory control in LH feedback at both the hypothalamic and pituitary levels. And the control condition is just as sharp: the authors did not record any change in LH and FSH secretion when pure androgen DHT was administered — DHT cannot be aromatised, and it does not suppress. What this explains: high aromatase expression in adipose tissue converts androgens to estrogens, which suppress GnRH, LH and FSH and therefore testosterone — hypogonadotropic hypogonadism, reported in 29 to 79 percent of obese men. And the trap: testosterone administration could increase estradiol production, further promoting the inhibitory feedback. Giving the hormone can deepen the suppression that caused the deficiency. The field states its own there is NO clear consensus on the role of estrogen receptor versus androgen receptor signaling in males. The aromatase-deficient men are decisive for estrogen; they do not prove androgen contributes nothing. doi 10.3389/fendo.2014.00001 · PMC10516609
The Two-Faced Peptide reduces it.
The evidence is electrophysiological and steroid-sensitive: stimulation of KNDy neurons by the NK3R agonist SENKTIDE was attenuated in intact versus castrated mice and suppression by dynorphin was enhanced. Both estradiol and DHT suppressed senktide-induced KNDy firing and enhanced the inhibition caused by dynorphin. The authors propose steroid modulation of responses to NK3R and kappa-opioid receptor activation as mechanisms for negative feedback in KNDy neurons. This is the cellular route for the other two edges: GnRH neurons carry no steroid receptors, so the feedback must land somewhere else — and it lands here, on the kisspeptin neuron, by making its dynorphin brake more effective. mouse brain-slice electrophysiology; the human arm is the aromatase-deficient men on the estrogen edge. doi 10.1210/en.2015-1741 · PMC10516609
Reproductive trigger increases it.
NBK558992 — GnRH is the hypothalamic input to the pituitary-gonadal axis.
Follicle-stimulating hormone increases it.
The pituitary arm of the axis. PMC9113536
What it drives
It increases Estrogen balance.
HPG-axis review 2025 — the hypothalamic-pituitary-gonadal axis (GnRH→LH/FSH) drives gonadal estradiol biosynthesis; FSH induces granulosa-cell aromatase to convert androgens to estrogen. PMC12448947
It increases Testosterone.
HPG-axis endocrinology review — pituitary LH stimulates testicular Leydig cells to synthesize testosterone. PMID 3109367. the axis is a closed feedback loop -- rising testosterone inhibits GnRH at the hypothalamus and LH at the pituitary, while inhibin selectively suppresses FSH only. Raising one arm is opposed by the loop. PMID 3109367
It increases Sperm quality.
HPG-axis endocrinology review — pituitary FSH, with high intratesticular testosterone, drives Sertoli-cell support of spermatogenesis. PMID 3109367. A precise limit from the primary: in selective gonadotrophin replacement in hypogonadotrophic hypogonadal men, qualitatively normal sperm production was achieved by replacing either LH OR FSH alone -- but both are required to maintain quantitatively normal spermatogenesis. Quality and count are separable endpoints and the axis does not deliver them together. The FSH requirement is greatest during initiation of sperm production at puberty. PMID 3109367
It reduces PCOS.
Named across five reviews of the cardiovascular-renal-hepatic-metabolic syndrome as part of the shared mechanism set: ectopic fat accumulation triggered by metabolic reprogramming, oxidative stress and inflammation induced by energy overload, modified lipids, UREMIC toxins, and senescence, as well as insulin resistance pathways activated by pro-inflammatory factors and lipotoxic products, collectively exacerbate simultaneous hepatic and renal injury. doi 10.1038/s41581-026-01066-0 · PMC11725408
It increases Women's hormone balance.
The genitalia and lower urinary tract share common estrogen receptor function. The receptor change is the estrogen receptors alpha and beta ARE present in the vagina, vestibule, urethra and bladder TRIGONE - while both receptors can be found in premenopausal women, only estrogen-beta receptors can be detected in postmenopausal women. The tissue does not merely see less hormone; it loses a receptor subtype. And a pH loop with a clinical endpoint: estrogen maintains vaginal glycogen, lactobacilli convert it to lactic acid holding pH at 3.5-5.0; loss of estrogen is responsible for the reduction of Lactobacillus, changing the vaginal fluid to an alkaline pH of 5.0 OR above, which promotes overgrowth of gram-negative rod fecal flora, inducing vaginal infection and UTI. Scale and underdiagnosis: GSM affects 40-54 percent of postmenopausal women and 15 percent of premenopausal women, and around 60 percent of these women have never had a diagnosis of GSM before. doi 10.3389/frph.2021.779398 · PMC10692865
It increases Urinary health.
The genitalia and lower urinary tract share common estrogen receptor function. The receptor change is the estrogen receptors alpha and beta ARE present in the vagina, vestibule, urethra and bladder TRIGONE - while both receptors can be found in premenopausal women, only estrogen-beta receptors can be detected in postmenopausal women. The tissue does not merely see less hormone; it loses a receptor subtype. And a pH loop with a clinical endpoint: estrogen maintains vaginal glycogen, lactobacilli convert it to lactic acid holding pH at 3.5-5.0; loss of estrogen is responsible for the reduction of Lactobacillus, changing the vaginal fluid to an alkaline pH of 5.0 OR above, which promotes overgrowth of gram-negative rod fecal flora, inducing vaginal infection and UTI. Scale and underdiagnosis: GSM affects 40-54 percent of postmenopausal women and 15 percent of premenopausal women, and around 60 percent of these women have never had a diagnosis of GSM before. doi 10.3389/frph.2021.779398 · PMC10692865
It increases Men's hormone balance.
The finding that unifies all three nodes is that the same androgen does opposite things in different tissues: testosterone acts directly, and indirectly through intracellular conversion to dihydrotestosterone by 5-alpha reductase, as in prostate cells, and separately through estrogen effect when converted to estradiol by aromatase. Raise testosterone and you also raise DHT and estradiol - which is why the same intervention supports male hormonal health and can enlarge the prostate. And the clinical data shows both arms at once: in 183 men over 50 with BPH, testosterone was significantly lower in patients with severe LUTS (285.94 ng/dL) than mild (544.09 ng/dL) - so low testosterone tracks with worse urinary symptoms, while DHT drives the gland. That is not a contradiction to resolve, it is two different molecules. Bidirectionality is explicit: the relationship between hypogonadism and metabolic disorders is bidirectional, and a vicious circle between the two components has been documented. PMC6669361
It increases Male fertility.
The finding that unifies all three nodes is that the same androgen does opposite things in different tissues: testosterone acts directly, and indirectly through intracellular conversion to dihydrotestosterone by 5-alpha reductase, as in prostate cells, and separately through estrogen effect when converted to estradiol by aromatase. Raise testosterone and you also raise DHT and estradiol - which is why the same intervention supports male hormonal health and can enlarge the prostate. And the clinical data shows both arms at once: in 183 men over 50 with BPH, testosterone was significantly lower in patients with severe LUTS (285.94 ng/dL) than mild (544.09 ng/dL) - so low testosterone tracks with worse urinary symptoms, while DHT drives the gland. That is not a contradiction to resolve, it is two different molecules. Bidirectionality is explicit: the relationship between hypogonadism and metabolic disorders is bidirectional, and a vicious circle between the two components has been documented. PMC6669361
It increases Female fertility.
The central finding is that reactive oxygen species ARE required, not merely harmful: ROS in the ovary regulate ovarian steroid hormone production, follicle synthesis, maturation, ovulation, and tubal function. ROS and antioxidant levels regulate the microenvironment of the follicular fluid, which determines which follicle becomes dominant. ROS can trigger ovulation in mature GRAAF follicles, and any change in this ROS level can disrupt ovulation. So an antioxidant claim here cuts both ways - the requirement is redox homeostasis, not suppression. Excess oxidative stress damages the oocyte through mitochondrial dysfunction, follicular atresia, meiotic errors, DNA damage and telomere shortening; too little disrupts the ovulatory trigger itself. Scale: infertility affects approximately 10-15 percent of couples, with nearly half the cases attributed to female reproductive dysfunction. doi 10.3390/antiox12081490 · PMID 40712896 · PMC10666387
It reduces Temperature stability in menopause.
10.3389/fphar.2025.1587885 — Drawn from reviews of neighboring outcomes rather than from studies of this outcome itself, which is weaker evidence, and the map marks it so. doi 10.3389/fphar.2025.1587885
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.