Human chorionic gonadotropin (HCG) is a glycoprotein hormone that acts as a structural and functional analog of luteinising hormone (LH) at the LH/CG receptor on Leydig cells. It is the primary gonadotropin of pregnancy, produced by syncytiotrophoblasts; in research it serves as the standard LH receptor agonist for studying testicular steroidogenesis, Leydig cell function, and HPG axis biology. In TRT research, HCG is the co-administration compound of choice for maintaining intratesticular testosterone (ITT) and testicular volume during exogenous testosterone suppression — making it essential for HPG axis preservation studies.
Mechanism of Action — HCG (Human Chorionic Gonadotropin)
HCG α-subunit is identical to LH, FSH, and TSH; the unique β-subunit (145 aa vs LH β 121 aa, with C-terminal extension) determines receptor specificity and extended half-life vs LH:
LH/CG receptor (LHCGR): Gs-coupled GPCR → cAMP/PKA → StAR protein → cholesterol → pregnenolone → testosterone (Leydig cells)
Testicular: Leydig cell testosterone synthesis (intratesticular testosterone, ITT, is 50–100× higher than serum) — essential for spermatogenesis
Sertoli cells: Indirect — ITT maintains Sertoli cell FSH-independent spermatogenic support
HPG feedback: LH negative feedback from exogenous testosterone → Leydig cell atrophy. HCG bypasses pituitary to directly stimulate LHCGR — maintaining ITT despite suppressed LH
Intratesticular testosterone — why serum levels are not the whole story
Spermatogenesis requires intratesticular testosterone (ITT) at concentrations 50–100× higher than serum testosterone. Exogenous TRT elevates serum T but suppresses LH → Leydig cells receive no stimulation → ITT falls → spermatogenesis impairs. Low-dose HCG (500 IU every 2–3 days) directly activates LHCGR and maintains ITT despite LH suppression. This is why HCG + testosterone combinations are the standard protocol in male fertility preservation research during TRT.
Key Research Studies & Clinical Data
Key HCG research studies
Study
Design
Key finding
Coviello et al. 2005
29 men on GnRH agonist + graded HCG doses
HCG 125 IU EOD maintained ITT and spermatogenesis — minimum effective dose established
Wenker et al. 2015
Retrospective TRT + HCG vs TRT alone
HCG maintained testicular volume and sperm parameters during TRT
Ramasamy et al. 2014
Hypogonadal men: TRT vs HCG monotherapy
HCG monotherapy increased T, maintained spermatogenesis; TRT increased T but suppressed sperm
Research Protocols — HCG (Human Chorionic Gonadotropin)
Protocol 1: HPG preservation during TRT (rat)
Testosterone cypionate 10mg/kg IM weekly + HCG 10–50 IU SC 3×/week vs T alone vs vehicle. Primary endpoints: testicular weight, ITT (LC-MS/MS), spermatogenesis (histology), Leydig cell number/morphology, FSH/LH, serum testosterone.
Protocol 2: Leydig cell steroidogenesis
HCG dose-response in isolated primary Leydig cells (rat). 0.01–100 mIU/mL. StAR expression (WB), progesterone/testosterone production (ELISA), cAMP (competitive binding), cell viability (MTT).
Orchidectomised rat model: HCG 25 IU SC 3×/week vs testosterone cypionate vs vehicle × 8 weeks. Serum testosterone, body composition, sexual behaviour, bone density, muscle mass.
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Frequently Asked Questions
What is HCG used for in research?
HCG is used as the standard LH receptor agonist in testicular steroidogenesis, HPG axis, and male fertility research. Its most common research application is HPG axis preservation during exogenous testosterone studies — maintaining intratesticular testosterone and spermatogenesis despite LH suppression from exogenous androgen.
How does HCG maintain fertility during TRT?
Exogenous testosterone suppresses pituitary LH secretion, depriving Leydig cells of their stimulation signal → intratesticular testosterone (ITT) falls dramatically despite elevated serum T. HCG directly activates LH/CG receptors on Leydig cells, maintaining ITT independent of pituitary LH — preserving spermatogenesis.
What is intratesticular testosterone and why does it matter?
Intratesticular testosterone (ITT) is testosterone measured within the testis — it is 50–100× higher than serum testosterone. This high local concentration is required for Sertoli cell-dependent spermatogenesis. TRT raises serum T but can suppress ITT by 95%+ via LH suppression.
What formats does QSC supply HCG in?
QSC supplies HCG as lyophilised research vials. Ships from domestic QSC warehouses in USA, EU, UK, Canada, and Australia.
Is HCG the same as pharmaceutical HCG (Pregnyl, Novarel)?
Pharmaceutical HCG is FDA-approved for specific human indications (infertility, cryptorchidism). QSC HCG is research-grade material supplied for laboratory research only. Same peptide sequence; ≥99% purity; not for human use.
Research Use Only: All QSC compounds are sold strictly for laboratory research purposes. Not for human use. Not approved by the FDA or equivalent regulatory bodies for human administration. All purchases confirm research intent and compliance with applicable local regulations.
