EVOLUTIONARY ASPECTS OF GONADOTROPIN-RELEASING-HORMONE AND ITS RECEPTOR

1. Gonadotropin-releasing hormone (GnRH) was originally isolated as a hypothalamic peptide hormone that regulates the reproductive system by stimulating the release of gonadotropins from the anterior pituitary. However, during evolution the peptide was subject to gene duplication and structural changes, and multiple molecular forms have evolved. 2. Eight variants of GnRH are known, and at least two different forms ar e expressed in species from all vertebrate classes: chicken GnRH II an d a second, unique, GnRH isoform. 3. The peptide has been recruited du ring;evolution for diverse regulatory functions: as a neurotransmitter in the central and sympathetic nervous systems, as a paracrine regula tor in the gonads and placenta, and as an autocrine regulator in tumor cells. 4. Evidence suggests that in most species the early-evolved an d highly conserved chicken GnRH II has a neurotransmitter function, wh ile the second form, which varies across classes, has a physiologic ro le in regulating gonadotropin release. 5. We review here evolutionary aspects of the family of GnRH peptides and their receptors.