HMG (human menopausal gonadotropin, also called menotropin) is a urine-derived gonadotropin preparation that carries both follicle-stimulating hormone (FSH) activity and luteinizing hormone (LH) activity, conventionally standardized at a 1:1 ratio and labeled in International Units (IU) rather than milligrams. In laboratory research it is used as a dual-receptor stimulus that engages the FSH receptor (FSHR) and the LH/choriogonadotropin receptor (LHCGR) simultaneously — a property that distinguishes it from single-agonist reference materials such as recombinant FSH or hCG. Analytical work published between 2003 and 2026 has established that most of the LH-receptor-mediated bioactivity in commercial HMG is contributed not by LH itself but by co-purified human chorionic gonadotropin (hCG). This article summarizes HMG's composition, receptor pharmacology, standardization, and laboratory handling. All information here is provided strictly for in-vitro and laboratory research use only.
What Is HMG?
HMG is not a single molecule. It is a purified protein mixture extracted from the urine of postmenopausal women, in whom circulating gonadotropins are elevated because ovarian negative feedback has been withdrawn. The material recovered from that source contains the glycoprotein hormone family members FSH and LH, plus a variable quantity of hCG, along with non-gonadotropin urinary proteins that survive purification.
All three of these gonadotropins share the same architecture: a non-covalently associated heterodimer built from a common 92-amino-acid alpha subunit and a hormone-specific beta subunit. FSH has an approximate molecular weight of 30 kDa and LH approximately 28 kDa, with carbohydrate accounting for a substantial fraction of each. Because the alpha subunit is identical across the family, receptor selectivity is determined entirely by the beta subunit — which is also why analytical methods that quantify the alpha subunit measure total gonadotropin content rather than any individual hormone.
CAS 9002-68-0 is assigned to menotropin as a preparation, not to a defined chemical entity. This is an important framing point: HMG behaves in the laboratory more like a standardized biological extract than like a synthetic peptide of known sequence and mass.
Two Hormone Activities, Three Gonadotropins
The most consequential finding in the HMG literature concerns where the LH activity actually comes from. In 2003, van de Weijer and colleagues published a compositional analysis of a commercial menotropin preparation in Reproductive BioMedicine Online. Using chromatographic and mass-spectrometric methods, they resolved three gonadotropins in the product — FSH, LH, and hCG — and reported that hCG immunoactivity was roughly three-fold higher than LH immunoactivity. Because hCG has a substantially longer circulating half-life than LH, the authors calculated that approximately 95% of the in-vivo LH-receptor-mediated bioactivity of the preparation was attributable to hCG rather than to LH.
That analysis has been reinforced by more recent work. In 2024, Capolupo and colleagues published an investigation in the International Journal of Molecular Sciences specifically designed to determine the origin of the hCG in highly purified HMG (HP-hMG). Their approach used sulfated glycans as a diagnostic marker: pituitary-derived glycoprotein hormones carry characteristic sulfated glycan structures that placental hCG does not. The glycan signature therefore distinguishes hCG that co-purified from postmenopausal pituitary output from hCG added from a separate placental (pregnancy-urine) source during manufacturing.
The practical implication for a research setting is direct. A vial labeled "75 IU FSH / 75 IU LH" does not contain 75 IU of LH protein. It contains a mixture whose LHCGR-directed bioactivity is dominated by hCG. Any experiment that depends on LH-specific rather than LHCGR-generic pharmacology — for example, work probing biased agonism between LH and hCG at the shared receptor — cannot treat HMG as an LH source.
Why HMG Is Labeled in IU, Not Milligrams
Like hCG, HMG is quantified by bioactivity rather than by mass. The reference method is the Steelman-Pohley bioassay, an in-vivo assay in immature female rats in which FSH is co-administered with a fixed dose of hCG and potency is read out from ovarian weight gain. Christin-Maitre and Bouchard reviewed the gonadotropin bioassay landscape in Methods in 2000, cataloguing the Steelman-Pohley assay alongside radioligand receptor assays and in-vitro Sertoli cell and granulosa cell bioassays.
The Steelman-Pohley assay remains the method published in the pharmacopoeias, but its limitations are well documented: limited precision, large animal requirements, and cumbersome data handling. A 2023 review in the International Journal of Molecular Sciences by Nevelli, Palmese and colleagues surveyed the transition from in-vivo potency determination toward in-vitro alternatives, motivated by both reproducibility and 3Rs considerations.
The most recent contribution here is a 2026 paper by Li and colleagues in Frontiers in Bioengineering and Biotechnology, which developed a reversed-phase HPLC method to quantify the alpha subunit common to FSH, LH, and hCG, along with FSH content and overall purity, in menotropin preparations. Validated to ICH Q2(R1), the method achieved correlation coefficients above 0.998 for both subunits, recoveries of 90.0-110.0% with relative standard deviations below 2.0%, and detection and quantification limits of 3 ng and 9 ng respectively. Across 69 commercial batches sampled at manufacturing, distribution, and clinical-use stages, the authors reported that the standard in-vivo bioassay showed substantial inter-assay variability and could not resolve subtle batch-to-batch fluctuations that the chromatographic method detected.
For laboratory work, this literature supports a simple rule: IU labeling on HMG is a potency assignment carrying real measurement uncertainty, not a precise mass statement. Investigators requiring tight quantitative control should verify content analytically rather than assuming label accuracy.
Receptor Pharmacology: FSHR and LHCGR
HMG's defining laboratory characteristic is that it stimulates two receptors at once.
The FSH Receptor
FSHR is a class A G protein-coupled receptor with a large leucine-rich-repeat ectodomain, a hinge region, and a seven-transmembrane core. Its canonical output is Gs-coupled adenylyl cyclase activation, raising intracellular cAMP and activating PKA, with additional signaling through PI3K/AKT and ERK1/2 branches and beta-arrestin recruitment.
The structural basis of hormone recognition was established by Fan and Hendrickson, who reported a 2.9-Šstructure of partially deglycosylated human FSH bound to the FSHR hormone-binding ectodomain in Nature in 2005. The hormone binds in what the authors described as a hand-clasp fashion to an elongated, curved receptor, burying an unusually large interface of approximately 2,600 Ų with high charge density. The binding mode appeared generalizable across the glycoprotein hormone family.
That picture was extended in 2012, when Jiang and colleagues reported in PNAS the structure of FSH bound to the entire FSHR ectodomain, including the hinge region. Contrary to expectation, the hinge did not form a separate structural module but was integral to the ectodomain fold, and it contributed a sulfotyrosine site that engages the hormone. The authors proposed a two-step interaction: initial ligand recruitment, followed by sulfotyrosine recognition that commits the complex to activation.
More recently, cryo-EM has resolved full-length receptor signaling complexes. Duan and colleagues published structures of full-length glycoprotein hormone receptor complexes in Nature in 2021, describing a "push and pull" activation mechanism in which the ectodomain is pushed by bound hormone and pulled by an extended hinge loop, with a conserved 10-residue fragment at the ectodomain-transmembrane interface acting as a tethered agonist. A 2023 Nature Communications paper from the same structural community addressed hormone- and allosteric-agonist-mediated FSHR activation specifically.
The LHCGR Arm
The LHCGR component of HMG's activity behaves, pharmacologically, as an hCG stimulus. LHCGR is the same receptor family member characterized in the hCG structural literature, and the 2021 cryo-EM work above resolved LHCGR in inactive and active states bound to chorionic gonadotropin and Gs.
In co-culture and whole-follicle model systems, this dual FSHR/LHCGR engagement is precisely why HMG is used rather than recombinant FSH alone: theca-cell LHCGR stimulation and granulosa-cell FSHR stimulation occur together, which more closely reproduces the two-cell, two-gonadotropin arrangement of ovarian steroidogenesis than a single-agonist stimulus does.
Glycoform Heterogeneity and In-Vitro Potency
Even setting aside the LH/hCG question, the FSH in HMG is not a uniform species. The FSH beta subunit carries N-linked glycosylation sites at Asn7 and Asn24, and preparations contain a mixture of fully glycosylated FSH (FSH24, both sites occupied) and hypo-glycosylated forms (FSH21/18, one site unoccupied).
This is not a cosmetic distinction. Jiang and colleagues reported in the Journal of Clinical Endocrinology & Metabolism in 2015 that hypo-glycosylated hFSH showed greater bioactivity than fully glycosylated recombinant hFSH in human granulosa cells, with faster receptor binding kinetics, higher apparent affinity, and occupancy of more FSHR binding sites under identical conditions.
Mechanistic follow-up has connected glycoform identity to receptor quaternary structure. A 2021 study in Frontiers in Endocrinology used super-resolution imaging (PD-PALM) in FSHR-expressing HEK293 cells and found that high concentrations of FSH21/18 rapidly dissociated FSHR oligomers into monomers while FSH24 did so with slower kinetics, and that low concentrations of either glycoform promoted oligomer association. Oligomer dissociation correlated with the time points at which higher cAMP production was observed.
For an investigator running FSHR assays, the takeaway is that glycoform composition is a real source of between-lot variability in urinary-derived FSH activity, and that dose-response curves generated with one lot may not superimpose on curves from another.
Purity and Co-Purified Proteins
Urinary derivation carries a purity cost that has been quantified repeatedly.
The 2003 van de Weijer analysis reported that non-gonadotropin proteins comprised at least 30% of the preparation by reversed-phase HPLC. In 2009, Bassett and colleagues published a proteomic comparison in Reproductive BioMedicine Online of urinary HMG, urinary hFSH, and recombinant hFSH, detecting 23 non-gonadotropin-related proteins at variable levels across batches of the urine-derived preparations, 16 of which had not previously been reported in urinary gonadotropins. The recombinant preparation was substantially purer than either urinary product.
Two practical consequences follow for laboratory use:
- Background protein can confound sensitive readouts. Co-purified urinary proteins may contribute to total-protein normalization, interfere in proteomic or immunoassay workflows, or exert their own activity in cell culture.
- Batch-to-batch variability is inherent, not incidental. The impurity profile varies across batches of the same product. Where a defined single-agonist stimulus is required, recombinant FSH is the more appropriate comparator, with HMG reserved for experiments that specifically require combined FSHR/LHCGR stimulation.
Laboratory Research Applications
Within in-vitro and preclinical model systems, HMG and related menotropin preparations appear in the published literature in several recurring roles:
- Dual-receptor stimulus. Simultaneous FSHR and LHCGR activation in granulosa-theca co-culture and whole-follicle models.
- Granulosa cell assays. cAMP accumulation, aromatase (CYP19A1) induction, and steroid output in primary or immortalized granulosa cell cultures.
- In-vitro follicle culture systems. Support of follicular development in three-dimensional and encapsulated follicle culture models.
- Analytical method development. Reference matrix for HPLC, mass spectrometry, and glycan-profiling methods, as in the 2024 and 2026 work above.
- Bioassay comparison. Head-to-head benchmarking of in-vivo Steelman-Pohley potency against in-vitro receptor-based alternatives.
- Purity and impurity profiling. Model system for proteomic characterization of urinary-derived biologics.
Handling, Reconstitution, and Storage
HMG is supplied as a lyophilized powder. Its handling requirements resemble those of other glycoprotein preparations more than those of small synthetic peptides.
Store lyophilized material at -20°C, protected from light and moisture. Allow vials to reach room temperature before opening so that condensation does not form on cold powder.
Reconstitute gently. Direct diluent slowly down the vial wall rather than onto the cake, and swirl rather than shake. Vigorous agitation of a glycoprotein solution promotes interfacial denaturation and aggregation, which reduces measured bioactivity without necessarily producing visible turbidity.
Aliquot to avoid freeze-thaw cycles. Repeated freezing and thawing is a recognized contributor to potency loss in gonadotropin preparations. Single-use aliquots of reconstituted material are preferable to repeated access of a single vial.
Expect the label to encode potency, not mass. Because IU assignment derives from a bioassay with documented variability, quantitative comparisons across lots should be anchored to an internal standard or an analytical measurement rather than to the label alone.
Verify with documentation. A certificate of analysis, independent purity testing, and endotoxin data are the relevant confirmations for a research-grade urinary-derived preparation, where co-purified protein content is a known variable.
Common Questions
What receptors does HMG act on?
Both the FSH receptor (FSHR) and the LH/choriogonadotropin receptor (LHCGR). This dual engagement is HMG's distinguishing pharmacological feature relative to recombinant FSH, which acts at FSHR alone, or hCG, which acts at LHCGR alone.
Is HMG a peptide?
No. HMG is a mixture of heterodimeric glycoproteins — FSH at roughly 30 kDa, LH at roughly 28 kDa, plus hCG — each built from two polypeptide chains carrying extensive N- and O-linked carbohydrate. Most research peptides are single synthetic chains under 5 kDa. The difference drives everything about how HMG is standardized, stored, and handled.
Does HMG contain real LH?
It contains LH protein, but published compositional analysis indicates that hCG, not LH, accounts for the large majority of LH-receptor-mediated bioactivity — approximately 95% by the 2003 estimate, owing to hCG's longer half-life and its higher relative abundance in the preparation. HMG is therefore not a suitable substitute for purified LH in experiments requiring LH-specific pharmacology.
How does HMG differ from HCG?
hCG is a single glycoprotein acting selectively at LHCGR and is supplied as a defined reference agonist for that receptor. HMG is a multi-component urinary extract whose defining property is combined FSHR and LHCGR stimulation. They are not interchangeable: HMG cannot be used as a clean LHCGR-selective stimulus, and hCG provides no FSHR activity at all.
Why is HMG measured in IU?
Because the material is a heterogeneous mixture of glycoforms and co-purified proteins, mass does not track biological activity. Potency is therefore assigned by bioassay — historically the Steelman-Pohley in-vivo assay — and expressed in International Units against a reference standard.
Is HMG studied for muscle growth or body composition?
No. That framing has no basis in the peer-reviewed gonadotropin literature and falls entirely outside the scope of this material. HMG supplied as a research chemical is intended for in-vitro and laboratory investigation of gonadotropin receptor signaling only. It is not for human consumption and is not intended to diagnose, treat, cure, or prevent any disease.
Why does batch-to-batch variability matter in FSHR assays?
Two independent sources compound: the glycoform ratio of FSH21/18 to FSH24, which measurably changes receptor binding kinetics and cAMP output, and the co-purified protein profile, which varies across batches of urinary-derived material. Both argue for running an internal reference within each experimental series rather than relying on nominal IU equivalence between lots.
Research Use Only
All products and information referenced here are supplied strictly for laboratory research use only. HMG is not a dietary supplement, is not approved for human or veterinary use, and is not intended to diagnose, treat, cure, or prevent any disease. Handling should be performed only by qualified personnel in an appropriate laboratory setting and in accordance with applicable institutional and regulatory requirements. Nothing in this article constitutes medical advice or a recommendation for use in humans or animals.
This article was researched and last updated August 2026 and incorporates analytical literature published through May 2026. Citations below link to indexed primary literature and peer-reviewed reviews.