Recent studies have provided evidence that 15??-hydroxytestosterone (15??-T) and 15??-hydroxyprogesterone (15??-P) are produced in vitro and in vivo in adult male sea lampreys (Petromyzon marinus), and that circulatory levels increase in response to injections with gonadotropin- releasing hormone (GnRH). We examined four species from the Petromyzontidae family including silver lampreys (Ichthyomyzon unicuspis), chestnut lampreys (I. castaneus), American brook lampreys (Lethenteron appendix), and Pacific lampreys (Entosphenus tridentatus) to determine if these unusual steroids were unique to sea lampreys or a common feature in lamprey species. In vitro production was examined through incubations of testis with tritiated precursors, and 15??-T and 15??-P production was confirmed in all species through co-elution with standards on both high performance liquid chromatography (HPLC) and thin layer chromatography. In vivo production was proven by demonstrating that HPLC-fractionated plasma had peaks of immunoreactive 15??-T and 15??-P that co-eluted with standards through using previously developed radioimmunoassays for 15??-T and 15??-P. The possible functionality of 15??-T and 15??-P was further examined in silver and Pacific lampreys by investigating the effect of injection of either type of lamprey GnRH on plasma concentrations of 15??-T and 15??-P. Injections with exogenous GnRH did not affect circulatory levels of either steroid in silver lampreys, and only GnRH III elicited higher levels of both steroids in Pacific lampreys. The 15??-hydroxylase enzyme(s) for steroids appeared to present in adult males of all species examined, but the question of whether 15??-hydroxylated steroids are functional in these lamprey species, and the significance of the 15-hydroxyl group, requires further research.
Additional Publication Details
Comparison of synthesis of 15??-hydroxylated steroids in males of four North American lamprey species