Effects of GnRH Antagonists Vs. Agonists in Domestic Carnivores

Gonadotropin-releasing hormone (GnRH) stimulates the pituitary secretion of both luteinizing and follicle-stimulating hormones, and thus controls the hormonal and reproductive functions of the gonads. GnRH analogs, which include agonists and antagonists, have been produced by amino acid substitutions of the native GnRH molecule to create greater potency and longer duration of effectiveness. While the development of agonists progressed quickly the antagonist´s has lagged behind, in part related to their high cost of production. Furthermore, the initial GnRH antagonist exhibited significant histamine release which almost halted their further development (1). More recently, a new series of potent, long acting, water soluble, low histamine-release third generation GnRH antagonists appeared including, among others, cetrorelix, abarelix, antarelix, teverelix, degarelix, azaline B and acyline. Long term administration of GnRH agonists functions through desensitization and down-regulation of GnRH pituitary receptors inhibiting gonadotropin production and release after an initial stimulation. Conversely, antagonists competitively block and inhibit GnRH-induced GnRH receptor gene expression leading to an immediate pituitary suppression (1) constituting their main advantage over the agonists. [...]