Effects of lamprey gonadotropin-releasing hormone-III on steroidogenesis and spermiation in male sea lampreys.

The biological activities of lamprey gonadotropin-releasing hormone-III (GnRH-III) were determined in the adult male sea lamprey, Petromyzon marinus. One injection of lamprey GnRH-III at 0.1 or 0.2 microgram/g body wt stimulated plasma estradiol and progesterone levels in adult male sea lampreys undergoing final maturation. Four successive injections of lamprey GnRH-III at 0.1 microgram/g of lamprey GnRH-1 at 0.2 microgram/g induced spermiation in 78 or 30% of the lampreys, respectively, compared to 0% in controls by Day 16. In summary, lamprey GnRH-III is biologically active in stimulating the pituitary-gonadal axis in adult male lampreys.