PepEvolutionGonadorelin is synthetic gonadotropin-releasing hormone (GnRH), the same 10-residue peptide the hypothalamus dumps into pituitary portal blood. It binds GnRH receptors on gonadotrophs and can raise luteinizing hormone (LH) and follicle-stimulating hormone (FSH). It is not kisspeptin, which sits one synapse upstream, and it is not leuprolide, a long-acting analog built to shut the axis down.
TL;DR
- One sequence. Porcine, ovine, and human GnRH are pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2. The Factrel label puts the free-base mass at 1182.33 daltons (Matsuo et al., 1971; Factrel PI).
- Minutes, not hours. Native GnRH’s half-life is 2 to 4 minutes, chopped by peptidases and cleared by glomerular filtration (Kumar and Sharma, 2014).
- The pattern is the drug. In rhesus monkeys with hypothalamic lesions, hourly pulses restored LH and FSH. Continuous infusion did not (Belchetz et al., 1978).
- Hoffman and Crowley, 1982: long-term pulsatile GnRH in men with idiopathic hypogonadotropic hypogonadism. Gonadotropins reached adult ranges in one week and were supraphysiologic by day 14. Testis size rose in four men. Three had sperm by 43 weeks (Hoffman and Crowley, 1982).
- Factrel is gone. The U.S. diagnostic product and its generics are discontinued. A research vial is not that product (Drugs.com).
What is gonadorelin, chemically?
It is native GnRH, made on purpose. Schally’s group proposed the porcine LH- and FSH-releasing sequence in 1971. The Factrel label later said the synthetic decapeptide matches the natural hormone isolated from porcine or ovine hypothalami (Matsuo et al., 1971; Factrel PI).
The chemistry is typical hypothalamic peptide: pyroglutamate at the amino end, glycinamide at the carboxyl end. Those caps slow exopeptidases. They do not make a depot drug.
That is why Peptides 101 treats GnRH as a releasing hormone, not a sex steroid and not a gonadotropin. For how a 10-mer like this is usually built today, see solid-phase synthesis.
How is gonadorelin different from kisspeptin?
Kisspeptin talks to GnRH neurons. Gonadorelin is the message those neurons send.
Kisspeptin-10 and kisspeptin-54 bind KISS1R (GPR54) on hypothalamic GnRH cells. Those cells then release GnRH into portal blood. Gonadorelin skips that step and occupies the pituitary receptor directly.
The comparison article is kisspeptin-10 and the HPG axis. A pituitary that still answers gonadorelin but not kisspeptin points upstream, at GnRH neurons or KISS1R.
Why does a 4-minute peptide need a pulse, not a drip?
Knobil’s monkeys made the rule. Belchetz, Plant, Nakai, Keogh, and Knobil lesioned the hypothalamus in rhesus monkeys so endogenous GnRH was gone. Hourly exogenous GnRH restored gonadotropin secretion. The same peptide, given continuously, did not (Belchetz et al., 1978).
Kumar and Sharma put the human pharmacology in one line: pulsatile GnRH induces FSH and LH. A continuous agonist, or a receptor-blocking antagonist, desensitizes the gonadotroph (Kumar and Sharma, 2014).
Forums treat gonadorelin like a long-acting “restart.” Native GnRH is a brief pulse. Stretch the occupancy and the pituitary stops answering.
What did the 1982 NEJM puberty study actually show?
Hoffman and Crowley treated men who had idiopathic hypogonadotropic hypogonadism with long-term pulsatile low-dose GnRH. Gonadotropins moved into the adult range within a week and overshot by day 14. Four men had larger testes, and three had sperm by 43 weeks (Hoffman and Crowley, 1982).
That is a pump study in a specific disease, not a protocol for a research vial. Conn and Crowley’s later NEJM review is the analog map: native GnRH as a pulse, substituted agonists as the drugs that exploit desensitization (Conn and Crowley, 1991).
Is gonadorelin the same molecule as leuprolide?
No. Same receptor, opposite clinical job.
Leuprolide, goserelin, triptorelin, and nafarelin are GnRH agonists with substitutions that resist peptidases. They flare LH and FSH, then down-regulate the receptor. That hypo-gonadal state is the point in prostate cancer, endometriosis, and precocious puberty (Kumar and Sharma, 2014).
Gonadorelin is the unmodified decapeptide. On the old Factrel label it was a single 100 mcg subcutaneous or intravenous bolus to test whether gonadotrophs could still fire. The label is explicit that one shot does not measure pituitary reserve (Factrel PI).
| Feature | Gonadorelin (native GnRH) | Kisspeptin-10 / -54 | Depot GnRH agonist (leuprolide class) |
|---|---|---|---|
| What it is | 10-residue hypothalamic peptide, pGlu…Gly-NH2 (Matsuo et al., 1971) | KISS1 fragments that hit KISS1R on GnRH neurons | Substituted analog with a longer half-life (Kumar and Sharma, 2014) |
| Direct target | Pituitary GnRH receptor | Hypothalamic GnRH neuron | Pituitary GnRH receptor, then desensitization |
| Clock | Half-life 2 to 4 min (Kumar and Sharma, 2014) | Minutes for kisspeptin-10, longer for kisspeptin-54 | Hours to a depot month |
| Pulse vs continuous | Hourly pulses restored LH/FSH in lesioned monkeys. Continuous infusion failed (Belchetz et al., 1978) | Drives endogenous GnRH pulses | Continuous occupancy is the design |
| U.S. product history | Factrel diagnostic, Lutrepulse pulsatile kit, both discontinued (Drugs.com) | No FDA-approved kisspeptin drug | Multiple approved depot products |
The Factrel pharmacology numbers are diagnostic, not a stack. After an intravenous 100 mcg bolus in adult men, mean time to the LH peak was 27 plus or minus 14 minutes. Mean LH peak was 63.8 plus or minus 40.3 mIU/mL (Factrel PI).
The same label recorded rare hypersensitivity after multiple doses, and one report of pituitary apoplexy with sudden blindness after GnRH in a patient who had a gonadotropin-secreting adenoma (Factrel PI).
Is a research vial the same as Factrel?
No. Factrel was an FDA-approved lyophilized diagnostic with a defined salt, lactose, and benzyl-alcohol diluent. Drugs.com states that the Factrel brand and any generics have been discontinued in the United States (Drugs.com).
A catalog vial labeled gonadorelin is not that product. Sequence on a website is not identity, purity, sterility, or dose accuracy. That gap is the point of how to read a COA.
Licensed hormone clinics, when they are the topic, sit in the provider directory and on the price index. Handling education lives on the reconstitution guide and the calculator.
Bottom line: Gonadorelin is real native GnRH. The 1971 sequence, the 2-to-4-minute half-life, and the Belchetz pulse rule are the story. Kisspeptin is upstream. Depot agonists are a different clinical tool. A research vial is not discontinued Factrel.
Educational only. Not medical advice. Not a recommendation to use gonadorelin, Factrel, Lutrepulse, kisspeptin, leuprolide, or any research-grade GnRH peptide.