Alarelin

Alarelin is a synthetic analog of gonadotropin-releasing hormone (GnRH) created by substituting D-alanine for glycine at position 6 of the natural GnRH decapeptide sequence. This modification significantly increases the peptide's resistance to enzymatic degradation and enhances its binding affinity for pituitary GnRH receptors, resulting in greater potency and longer duration of action compared to native GnRH.

Like other GnRH agonists, alarelin initially stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. With continued administration, it induces pituitary GnRH receptor downregulation, leading to suppression of the reproductive axis and reduced gonadal steroid production. This dual-phase pharmacology — initial stimulation followed by suppression — is characteristic of all GnRH agonist compounds.

Alarelin has been most extensively used in veterinary medicine, particularly in aquaculture for inducing spawning in fish species and in livestock reproduction management. In fish, alarelin is commonly combined with a dopamine antagonist (such as domperidone) to enhance gonadotropin release and induce ovulation. This application has been particularly valuable in captive breeding programs for endangered fish species and in commercial aquaculture.

In human medicine, alarelin has been used primarily in China and some Asian countries for controlled ovarian stimulation in assisted reproductive technology (ART) protocols, similar to other GnRH agonists. Research has also explored its potential utility in the treatment of hormone-dependent conditions. However, its clinical use in humans is more limited compared to triptorelin, leuprolide, and other more widely adopted GnRH agonists.