Gonadorelin Acetate 5mg Peptide

Gonadorelin is the decapeptide pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2, the same molecule hypothalamic neurons release into the hypophysial portal circulation to control the pituitary. It is gonadotropin-releasing hormone itself, not an analogue of it. The free base is C55H75N17O13 at 1,182.3 g/mol, CAS 33515-09-2, PubChem CID 638793. Leuprolide, triptorelin, goserelin and buserelin all carry deliberate substitutions at position 6 and at the C-terminus. Gonadorelin carries none, which is why it remains the reference compound when the question is how the native axis behaves rather than how a modified agonist behaves.

The word acetate on the label names the counterion, not a different molecule. Peptides purified by reversed-phase HPLC come off the column as trifluoroacetate salts, and the acetate form is produced by exchanging that counterion, since acetate is far less likely than residual TFA to interfere with cell-based assays. The acetate salt is C57H79N17O15 at 1,242.3 g/mol, PubChem CID 11980076, and registries carry separate CAS numbers for the anhydrous acetate (34973-08-5), the monoacetate (499785-55-6) and the diacetate tetrahydrate (52699-48-6). A vial labelled by gross mass therefore holds less peptide than the number suggests, because part of that mass is acetate and bound water.

The fact that organises everything else about this molecule is pulsatility. Delivered in discrete pulses, gonadorelin drives luteinizing hormone and follicle-stimulating hormone release. Delivered continuously at the same total exposure, it shuts that release down by desensitising and downregulating its own receptor. Both directions were demonstrated in the same animals in the same 1978 experiment, and the suppressive direction is the entire basis of the long-acting agonists.

Gonadorelin binds the type I GnRH receptor (GNRHR) on pituitary gonadotropes, a class A G protein-coupled receptor signalling predominantly through Gq/11. Receptor occupancy activates phospholipase C beta, generating inositol trisphosphate and diacylglycerol, raising intracellular calcium, and driving both immediate exocytosis of stored LH and transcription of the gonadotropin subunit genes. Millar and colleagues catalogued 23 structural variants of GnRH across protochordates and vertebrates in their 2004 receptor review, and noted that the mammalian type I receptor is unusual among GPCRs in lacking a cytoplasmic C-terminal tail, the domain that normally recruits arrestin and drives rapid internalisation.

Clearance is fast because the peptide is built to be cleared fast. Lew and colleagues showed in 1994, working with ovine hypothalamic extracts and recombinant rat endopeptidase EC 3.4.24.15, that degradation proceeds in two steps: prolyl endopeptidase first removes the C-terminal Gly10 amide to give GnRH(1-9), then EP24.15 cleaves the Tyr5-Gly6 bond to give GnRH(1-5). Affinity of EP24.15 for the intact peptide was low (Km 1.35 mM) and improved 10 to 15 fold once the C-terminal amide or the whole glycinamide was removed (Km 90 and 119 micromolar). That is direct evidence that the blocked C-terminus is what protects the intact hormone from the enzyme that finishes it.

The measured consequence in humans is a two-phase disappearance curve. Seyler reported in 1975 that after a 100 microgram intravenous bolus of synthetic LHRH in normal men, peak biological activity in peripheral blood appeared within 2 to 6 minutes and the decay resolved into two exponentials with half-lives of roughly 2 and 10 minutes. Estrogen pretreatment suppressed the pituitary LH response without changing those clearance rates, which located the effect at the pituitary rather than in the circulation.

That short life is a feature rather than a limitation. Because each pulse is cleared before the next arrives, the receptor is free to resensitise between pulses, and the gonadotrope reads pulse frequency as a signal in its own right. Hold the concentration steady and the signal disappears: the receptor pool downregulates, second messenger coupling falls away, and gonadotropin output collapses despite continuous ligand.

Two laboratories arrived at the same ten residues within months of each other in 1971, from different starting material. Matsuo, Baba, Nair, Arimura and Schally proposed the amino acid sequence of the porcine LH- and FSH-releasing hormone in Biochemical and Biophysical Research Communications in June. Burgus, Butcher, Ling, Monahan, Rivier, Fellows, Amoss, Blackwell, Vale and Guillemin published the molecular structure of the ovine LRF in Comptes Rendus later that year. The sequences matched. That established GnRH-I as conserved across mammals and made a single synthetic decapeptide useful in every mammalian species studied since.

Roger Guillemin and Andrew Schally shared the 1977 Nobel Prize in Physiology or Medicine for their discoveries concerning peptide hormone production of the brain, with Rosalyn Yalow recognised the same year for radioimmunoassay. The pairing matters for reading the older literature. Without the assay there was no way to measure the LH response that defined the hormone's activity, and a great deal of 1970s gonadorelin work is really work on what a new assay had just made visible.

Both groups reached the sequence by exhaustive extraction from animal hypothalami, Schally's from pig and Guillemin's from sheep, at a scale that took years of tissue collection. What they isolated had a blocked N-terminus (pyroglutamate) and a blocked C-terminus (glycinamide), an arrangement that made the Edman chemistry of the period considerably harder than it would have been for an ordinary peptide, and that also turns out to be the structural reason the molecule survives in plasma for minutes rather than seconds.

The 1978 Science paper by Belchetz, Plant, Nakai, Keogh and Knobil is why gonadorelin is interesting rather than merely historical. Their preparation was a rhesus monkey with a hypothalamic lesion that had reduced circulating LH and FSH to undetectable levels, so any gonadotropin measured afterwards had to come from the exogenous peptide. Continuous infusion of GnRH into that animal did not restore sustained secretion. Hourly pulses of the same peptide did. Switching an animal that was secreting normally on hourly pulses over to continuous infusion turned the secretion off again.

Wildt and colleagues then took the preparation apart parameter by parameter in Endocrinology in 1981, using a baseline of 1 microgram per minute for 6 minutes once every hour. Increasing frequency to two, three and five pulses per hour, with infusion rate and pulse duration unchanged, produced progressive falls in plasma gonadotropins, and those falls were traceable to reduced pituitary responsiveness to each individual pulse rather than to anything upstream. Decreasing frequency to one pulse every three hours produced variable LH declines but a consistent FSH rise. Dropping the infusion rate from 1 to 0.1 micrograms per minute while holding frequency and duration constant sent both hormones to immeasurable levels.

Two conclusions follow, and they are the load-bearing facts for anyone designing an experiment with this peptide. A GnRH exposure has at least three independent variables, frequency, amplitude and duration, so reporting only an amount describes almost nothing about what the pituitary actually saw. And the LH to FSH ratio is itself a readout of frequency, which is why slow pulsing favours FSH while fast pulsing favours neither.

The analogues were designed against the specific weaknesses the degradation studies exposed. Cleavage at Tyr5-Gly6 by endopeptidase EC 3.4.24.15 is the main proteolytic exit, and glycine at position 6 sits in the beta turn the receptor recognises. Replacing it with a D-amino acid does two things at once: it blocks that cleavage sterically and it stabilises the bioactive conformation, raising receptor affinity. Leuprolide is [D-Leu6, des-Gly10, Pro9-ethylamide] GnRH. Triptorelin is [D-Trp6] GnRH. Goserelin carries D-Ser(tBu) at position 6 with an azaglycine amide at the C-terminus. Buserelin combines D-Ser(tBu)6 with the same ethylamide C-terminus leuprolide uses.

Those substitutions convert a peptide with a two-minute initial half-life into agents that can be formulated as one-month and three-month depots. Once exposure is continuous, the receptor does what Belchetz showed it does under continuous exposure: it downregulates, and gonadotropin output collapses. The suppression that makes leuprolide useful in hormone-sensitive prostate and breast disease is therefore not a different pharmacology from gonadorelin. It is the same pharmacology with the pulse interval engineered out.

That mechanism leaves a signature. Because an agonist must occupy and activate the receptor before it can desensitise it, depot agonists produce an initial testosterone surge, and repeat administration can produce microsurges. GnRH antagonists, a structurally distinct group including cetrorelix, ganirelix and degarelix that carry multiple substitutions and block the receptor without activating it, suppress testosterone rapidly with no surge at all. Boccon-Gibod and colleagues reviewed the comparison in 2011 and identified the absent surge as the main practical distinction of the antagonist class in advanced prostate cancer.

Gonadorelin sits outside both groups. It is neither a long-acting agonist nor an antagonist. It is the native ligand, which is exactly why it stays in use when the experimental question is about the axis rather than about a drug.

The short half-life that makes gonadorelin awkward for sustained suppression makes it well suited to a provocation test. A single exposure produces a bounded LH and FSH excursion that has resolved within a few hours, so pituitary gonadotrope reserve can be read from the peak. This is the basis of the gonadorelin stimulation test used to separate central precocious puberty from peripheral causes, and to distinguish pituitary from hypothalamic failure in hypogonadotropic hypogonadism. The ATC system gives gonadorelin a dedicated diagnostic code, V04CM01, alongside its endocrine code H01CA01, which is unusual for a peptide and reflects how much of its documented use is measurement rather than treatment.

The threshold in common use is a peak LH above 5.0 U/L. A retrospective review of 234 Korean girls diagnosed on that criterion found body mass shifts the peak: overweight girls reached 8.95 U/L against 11.97 U/L in normoweight girls, with a parallel difference in peak FSH. A 2025 report in the same journal asked directly whether the triptorelin stimulation test is interchangeable with the gonadorelin test in boys, which is the question that arises wherever a centre substitutes an analogue for the native peptide and needs to know whether the published thresholds still apply.

Massachusetts General Hospital ran the longest-lived study of this class, NCT00392756, from April 1989 to May 2019, enrolling 624 participants to examine the role of gonadotropin pulsations in reversal of hypogonadotropic hypogonadism, with GnRH as the sole listed intervention. Thirty years on one protocol is unusual, and it is a fair proxy for how settled the underlying pharmacology is.

Three compounds in this catalogue act on the hypothalamic-pituitary-gonadal axis at three different levels, and the differences are structural rather than a matter of potency. Kisspeptin-10 acts upstream, on KISS1R receptors expressed by the GnRH neurons themselves. Gonadorelin acts at the pituitary gonadotrope. hCG acts downstream at the gonad, on the LH and choriogonadotropin receptor, bypassing hypothalamus and pituitary entirely.

The dependency was demonstrated directly in adult male rhesus monkeys. A 50 microgram intravenous bolus of human kisspeptin-10 produced a single LH pulse followed by a testosterone rise sustained for at least 180 minutes. That response was abolished in animals pretreated with the GnRH receptor antagonist acyline, which places kisspeptin unambiguously above GnRH in the chain. In the same acyline-blocked animals kisspeptin still raised hCG-stimulated testosterone, revealing a separate action at the testis itself.

For experimental design the consequence is direct. A kisspeptin challenge asks whether the GnRH neuron can be driven. A gonadorelin challenge asks whether the gonadotrope can respond. An hCG challenge asks whether the gonad can respond. Seminara and colleagues showed in 2003 that loss-of-function GPR54 mutations cause hypogonadotropic hypogonadism in both humans and mice while the mice stayed responsive to exogenous GnRH and to gonadotropins, which is the genetic version of the same three-level dissection.

Peptide content and gross mass are not the same number for an acetate salt. Acetate and residual water contribute mass, roughly 60 g/mol per acetate equivalent against a 1,182.3 g/mol backbone. Anyone calculating molarity from a labelled mass should work from the free base weight and from the peptide content stated on the certificate of analysis rather than from vial mass, and should note whether the material is the acetate, the hydrochloride (the salt used throughout the veterinary literature) or the free base, since the same quantity of peptide appears as three different numbers depending on which is quoted.

The lyophilised powder is the stable form. In solution the peptide is attacked by the same prolyl endopeptidase and EP24.15 chemistry that clears it in vivo, and any protease activity carried in with the diluent works on the Tyr5-Gly6 and Pro9-Gly10 bonds specifically. Repeated freeze-thaw cycling is the common avoidable loss of assayable material. The C-terminal glycinamide deserves attention for a second reason: the 1994 kinetics showed that removing it raises EP24.15 affinity by more than an order of magnitude, so the first degradation product is a better substrate than the parent compound.

Analytical work on this specific peptide has been driven by anti-doping requirements, because gonadorelin appears on the World Anti-Doping Agency prohibited list as a peptide hormone on the basis that raising endogenous LH raises testosterone. Torrini and colleagues reported a biomimetic ELISA in 2022 built on polynorepinephrine molecularly imprinted polymers grown directly on microwells, reaching a detection limit of 277 pmol/L with coefficients of variation of 4.07 percent in standards and 5.24 percent in urine, cross-validated against mass spectrometry. The same group reviewed the wider analytical position of small peptide hormones in 2023 using gonadorelin as the worked example, and that pair is the current methods reference for characterising this material.

Formulation chemistry has taken a different route. Yordanova and colleagues showed in 2018 that the enzymatically stabilised derivative GnRH [6-D-Phe] self-assembles into oligomers and fibrils when Zn(2+) is present and the pH is shifted, and that the lyophilised zinc complex released peptide slowly and continuously over 14 days from two different oil vehicles. That work is on the D-Phe6 derivative rather than on native gonadorelin, and the distinction is the point: the native peptide is the one that does not survive long enough to be depot-formulated that way.

The largest and most recent controlled datasets on native gonadorelin come from cattle rather than from human medicine, because timed-breeding programmes in dairy herds deliver statistical power that clinical endocrinology rarely reaches. A 2026 four-herd study across California and Wisconsin blocked 6,621 lactating Holsteins in a two by two factorial design by parity and by gonadorelin hydrochloride quantity at the first GnRH of a synchronisation programme. The larger quantity raised peak LH and LH area under the curve in a serially sampled subset, raised ovulatory response from 70.8 to 83.0 percent by ultrasonography, and raised pregnancy per artificial insemination from 48.6 to 51.8 percent, with the benefit concentrated in multiparous cows.

Earlier work in the same journal tested the equivalent comparison in Holstein heifers and in resynchronisation programmes, and a 2017 study in Theriogenology compared LH surge profiles between gonadorelin and the analogue buserelin across seasons and stages of the estrous cycle. That is one of the few head-to-head native-versus-analogue pharmacodynamic comparisons available in any species, and it exists because livestock work routinely runs both compounds side by side.

This literature is useful to a research buyer for a specific reason. It reports species, quantity, salt form, sampling schedule and endpoint with a consistency the human literature on this peptide rarely matches, and the effect sizes are large enough that the relationship between amount and response is visible rather than inferred.