The gonadotropin-releasing hormones (GnRH) (gonadoliberin) [<cite idref="PUB00005538"/>] are a familyof peptides that play a pivotal role in reproduction. The main function ofGnRH is to act on the pituitary to stimulate the synthesis and secretion ofluteinizing and follicle-stimulating hormones, but GnRH also acts on thebrain, retina, sympathetic nervous system, gonads and placenta in certainspecies. There seems to be at least three forms of GnRH. The second form isexpressed in midbrain and seems to be widespread. The third form has only beenfound so far in fish.GnRH is a C-terminal amidated decapeptide processed from a larger precursorprotein. Four of the ten residues are perfectly conserved in all specieswhere GnRH has been sequenced. Gonadotropin-releasing hormone