Gonadal steroids: Synthesis, plasmatic levels and biological activities in sturgeons

Abstract

The information on sex steroids in sturgeons is fragmented and comes from different species. In females, circulating oestradiol-17ß increases during vitellogenesis and resulted a good marker of puberty in some species. However, researchers failed to induce oocyte growth and vitellogenesis using treatments with oestradiol-17ß. Androgens also increase during this period but remained elevated during ovulation and post-ovulation suggesting a physiological role at peri-ovulatory period. 17,20,21P seems to be a good candidate as mediator of gonadotropin to induce follicle maturation since it is produced in vitro by sturgeons ovaries, it has a high potency to induce follicle maturation in vitro, and its plasmatic concentration increases after hormonal induction of ovulation; however, other C21 steroids as 17,21-dihydroxy-4-pregnene-3,20-dione (17,21P), 17,20ß-dihydroxy-4-pregnen- 3-one (17,20ßP) and 17,20ß-dihydroxy-4-pregnen-3-one (17,20ßP) need to be further investigated as possible maturation-inducing steroids. Studies on potency of C21 and C19 steroids to induce resumption of meiosis revealed that C21 steroids are more potent than testosterone and that 11-oxygenated androgens do not induce maturation. Aromatase expression in immature males and plasmatic changes of testosterone and oestradiol-17ß suggest their participation in early testicular development. 11-Ketotestosterone increased significantly during spermatogenesis both in vitro and in vivo as it has been shown in teleosts. The C21 steroid (17,20ßP and 17,20,21P) increases in blood plasma after hormonal induction of spermiation suggesting their participation in the control of sperm maturation and release. Biological activity of steroids and in vitro steroid production by gonads are almost none studied in sturgeons.