Fig. 4. Chemical structure of the hypothalamic decapeptide gonadotropin-releasing hormone (GnRH). Amino acids 2 and 3 are important for receptor activation. Degradation of GnRH occurs by cleavage of the decapeptide between amino acids 5–6 and 6–7. (Friedman AJ: Leuprolide acetate: Applications in gynecology. Curr Probl Obstet Gynecol Fertil 11:209, 1988)