Comparative Biological Properties of Lamprey Gonadotropin-releasing Hormone in Vertebrates

The biological activities of lamprey GnRH were determined in the lamprey, chicken, sheep, and rat. Lamprey GnRH elevated plasma steroid levels and stimulated ovulation in the lamprey, but had little or no LH-releasing activity in chicken and sheep pituitary bioassays or effect on GnRH receptor-binding activity in the rat pituitary. The lamprey GnRH molecule is structurally distinct from other known vertebrate GnRHs and is the first identified molecule in this family to have different amino acids in the third and sixth positions. These data suggest that the presence of Tyr3 or Glu6 in lamprey GnRH may account for the lack of biological activity in the representatives of the two different vertebrate classes investigated in this study.