Overview
In plain English
HCG is a glycoprotein hormone, not a peptide. It is best known as the pregnancy hormone, but in research it is used because it acts on the same receptor as luteinising hormone — the LH/CG receptor on Leydig, theca and granulosa cells.
It is studied in published research as an LH surrogate in gonadal steroidogenesis models, and in work on the respective roles of LH and FSH under experimental gonadotropin suppression. Strictly for laboratory research use. Not for human or veterinary consumption.
- What it isA heterodimeric glycoprotein hormone acting at the LH/CG receptor
- Mainly studied forGonadal steroidogenesis and gonadotropin-suppression research models
- Supplied asLyophilised powder, 5,000iu and 10,000iu vials, independently assayed
How it works
What it actually does
Gonadal steroid production runs on a pituitary signal, luteinising hormone. When that signal is suppressed in a research model, Leydig cell steroidogenesis falls with it.
HCG binds the same receptor as that signal. In published models, receptor occupancy raises cAMP and drives the steroidogenic pathway in the absence of endogenous LH.
It persists far longer in circulation than native LH, because of additional sialylated glycans on a C-terminal extension of its beta subunit — which is why it serves as a sustained stimulus in experimental work.
The science in detail
HCG is not a peptide in the sense that most of this catalogue is. It is a heterodimeric glycoprotein hormone, produced by the syncytiotrophoblast during pregnancy, and it belongs to the same structural family as luteinising hormone, follicle-stimulating hormone and thyroid-stimulating hormone. All four share a common alpha subunit; specificity resides entirely in the beta subunit, which associates non-covalently with the alpha chain to form the active hormone. Neither subunit is active alone.
The target is the luteinising hormone / choriogonadotropin receptor, a class A G-protein-coupled receptor expressed on Leydig cells in the testis and on theca and granulosa cells in the ovary. Receptor occupancy activates adenylate cyclase, raises cAMP and drives protein kinase A signalling, with steroidogenic acute regulatory protein mobilising cholesterol to the inner mitochondrial membrane as the rate-limiting step in steroid synthesis.
HCG and LH act at the same receptor, which is why HCG functions experimentally as an LH surrogate. The pharmacologically significant difference is duration. The HCG beta subunit carries a C-terminal peptide extension bearing additional O-linked glycosylation, and this heavily sialylated tail markedly slows renal clearance. The result is a far longer circulating half-life than native LH, which is what makes the molecule useful as a sustained stimulus in gonadal research models.
The human literature is substantial and long-established. Matsumoto, Karpas and Bremner (Journal of Clinical Endocrinology & Metabolism, 1986) administered HCG chronically to normal men, suppressing FSH to undetectable levels, and demonstrated that FSH replacement was required to restore quantitatively normal sperm production — establishing the division of labour between the two gonadotropins. Coviello et al. (Journal of Clinical Endocrinology & Metabolism, 2005) reported that low-dose HCG maintained intratesticular testosterone in normal men with testosterone-induced gonadotropin suppression, a study frequently cited in subsequent work on gonadal axis suppression.
Because it is a glycoprotein rather than a synthetic peptide, batch characterisation and handling differ meaningfully from the rest of this catalogue.
Evidence
What the research shows
Acts at the same receptor as LH
It substitutes for the pituitary LH signal in research models where that signal has been suppressed.
Much longer-lasting than native LH
Structural differences give it a far longer circulating half-life, so it acts as a sustained receptor stimulus.
Intratesticular testosterone maintained in a published study
A clinical pharmacology study reported intratesticular testosterone maintained under experimental gonadotropin suppression.
Shares structure with LH, FSH and TSH
It belongs to the same hormone family; only one half of the molecule gives it its specificity.
Reconstitution & handling
Reconstitution and handling in the laboratory
These are general handling notes for the lyophilised glycoprotein supplied by Purist Peptides. They describe the preparation of a stock solution for laboratory work. They are not a dosing protocol, and they describe no administration to a person or an animal.
A 3ml vial of bacteriostatic water is included free with every peptide vial you order, so the material can be reconstituted on arrival.
HCG 5,000iu and 10,000iu — preparing a stock solution
Choice of diluent
Bacteriostatic water (water for injection with 0.9% benzyl alcohol) is the usual diluent where a stock will be drawn from repeatedly, because the preservative permits several septum entries across a working period. Sterile water for injection and sterile 0.9% sodium chloride are both used where a single-use preparation is wanted instead. The diluent volume sets the concentration of the stock, so record it.
Sterile technique
- Allow the sealed vial to reach room temperature before opening the carton — reconstituting a cold lyophilised cake slows dissolution
- Work in a clean area or a laminar flow cabinet, and wipe the rubber septum with 70% isopropyl alcohol, letting it dry fully
- Draw the chosen volume of diluent using a sterile single-use syringe and needle
- Angle the needle so the diluent runs down the inside wall of the vial — do not direct the stream onto the lyophilised cake
- Roll the vial gently between the palms until the cake has dissolved completely. Do not shake and do not vortex: HCG's two subunits are held together non-covalently and dissociate under shear and interfacial stress, with loss of activity and no visible change
- Let the vial stand for 5 to 10 minutes. A correctly reconstituted solution is clear and free of visible particles
Working out the concentration
Concentration follows from the mass in the vial and the volume of diluent added, nothing else. For a glycoprotein the concentration is expressed in international units per millilitre. Adding 1ml of diluent to the 5,000iu vial gives a 5,000iu/ml stock; adding 2ml to the 10,000iu vial gives the same 5,000iu/ml. Label every reconstituted vial with its concentration and the date it was prepared.
Storage and stability
Before reconstitution
The lyophilised powder is the stable form. Sealed vials are best held at −20°C, protected from light and from moisture; the short periods at 2 to 6°C that occur in transit and on arrival are expected and are accounted for in the supply chain. Keep the vial in its carton — light and humid air are the two ordinary causes of loss on storage.
After reconstitution
Hold reconstituted solution at 2 to 6°C and protect it from light. Do not freeze a working stock: freeze-thaw cycling is the main avoidable cause of degradation and of visible precipitate, and a glycoprotein is more vulnerable to it than a short synthetic peptide.
Reconstituted HCG has a shorter stability window than the synthetic peptides in this range. Use the stock within a short working period, avoid repeated agitation, and do not freeze it.
Checks before use
Inspect every vial against a light source. Discard any solution that is hazy, discoloured or contains particles, and any vial whose septum integrity is in doubt. The independent HPLC assay report for the batch supplied is available on request.
Strictly for laboratory research use. Not for human or veterinary consumption.
Questions
Frequently asked questions
Why is HCG measured in international units rather than milligrams?
Because it is a glycoprotein whose activity depends on glycosylation as well as sequence, potency is defined against a biological reference standard rather than by mass. Two preparations of identical mass may differ in activity, so international units are the meaningful specification.
How does HCG differ from luteinising hormone?
Both act at the same receptor. The difference is duration: the HCG beta subunit carries a C-terminal peptide extension with additional sialylated O-linked glycans, which slows renal clearance substantially and gives a far longer circulating half-life than native LH.
What has HCG been studied for in the research literature?
Gonadal steroidogenesis, intratesticular testosterone, and the respective roles of LH and FSH in spermatogenesis. Matsumoto et al. (JCEM, 1986) and Coviello et al. (JCEM, 2005) are two frequently cited examples. Purist supplies the compound for laboratory research only.
Why does it require different handling from the synthetic peptides?
It is a much larger molecule held together by a non-covalent association between two subunits. That association can be lost to shear or interfacial stress without any visible change in the solution, and activity is lost with it. Reconstituted stability windows are also shorter.
How is purity verified?
Every batch is assayed by independent HPLC at Bioindustrial Services in Boksburg. We do not rely on the manufacturer's own certificate alone. The assay report for the batch you receive is available on request, and our full testing protocol is set out at Quality Standards.
How long does delivery take?
Orders are dispatched from South Africa, with timelines varying by region and courier. Current dispatch and transit windows are set out at Delivery Process.
What is the returns policy?
Unopened vials in original condition may be returned under the conditions set out at Refund Policy.
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