Alarelin

Overview

Alarelin is a synthetic gonadotropin-releasing hormone (GnRH) agonist decapeptide developed primarily in China and the Soviet Union for veterinary and limited human reproductive applications. Structurally similar to gonadorelin and leuprolide, alarelin features targeted amino acid substitutions that dramatically enhance its potency and resistance to enzymatic degradation. It is commonly used in animal reproduction for estrus synchronization, ovulation induction, and breeding program management, and has been investigated for human endometriosis and precocious puberty.

Alarelin belongs to the broader family of GnRH analogs alongside buserelin, nafarelin, triptorelin, and histrelin. Its commercial footprint is largest in veterinary medicine in Asia, while in Western markets more established human GnRH agonists dominate.

Structure / Sequence

Alarelin has the sequence pGlu-His-Trp-Ser-Tyr-D-Ala-Leu-Arg-Pro-NHEt. The key modifications from native GnRH are the substitution of D-alanine at position 6 (replacing glycine) and replacement of the C-terminal Gly-NH2 with an N-ethyl proline amide. These changes protect the peptide from endopeptidase cleavage and increase receptor affinity roughly 50-fold over native GnRH.

Mechanism of Action

Alarelin binds the GnRH receptor (GnRHR) on anterior pituitary gonadotropes. Initial administration triggers an acute release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), the "flare" effect. Chronic or pulsatile exposure causes receptor downregulation and desensitization, suppressing gonadotropin secretion and ultimately gonadal steroid production, the pharmacologic basis for "medical castration" used in hormone-responsive cancers and endometriosis.

In veterinary settings, acute alarelin dosing is timed to induce ovulation in cows, sows, and ewes, often in combination with prostaglandin F2-alpha protocols.

Research Summary

Pharmacokinetics

Subcutaneous or intramuscular alarelin reaches peak plasma concentrations within 30 to 60 minutes. Plasma half-life is approximately 2 to 4 hours, intermediate between native GnRH (minutes) and long-acting depots such as leuprolide microspheres. Elimination is predominantly renal following hepatic peptidase degradation.

Dosing Protocols

Clinical and veterinary dosing of alarelin varies widely:

• Cattle ovulation induction: 10 to 25 mcg IM at defined cycle time points
• Swine synchronization: 5 to 10 mcg IM
• Human investigational use: 150 to 300 mcg intranasal twice daily (historical endometriosis protocols)

Alarelin is not FDA-approved in the United States. Human therapeutic use should rely on approved GnRH agonists instead.

Common Discussion Topics

• Comparison of alarelin potency to gonadorelin and buserelin
• Role of D-amino acid substitutions in extending GnRH analog half-life
• Veterinary reproductive synchronization programs using alarelin
• Regulatory differences driving alarelin's limited Western availability
• Flare effect management when initiating GnRH agonist therapy

Related Compounds

• Gonadorelin — native GnRH decapeptide
• Leuprolide — long-acting GnRH agonist
• Buserelin — clinical GnRH agonist
• Triptorelin — depot GnRH agonist
• Nafarelin — intranasal GnRH agonist
• Histrelin — implant GnRH agonist
• Degarelix — GnRH antagonist