Seasonal changes in the production of two novel and abundant ovarian steroids in the channel catfish (Ictalurus punctatus).

Timely and appropriate changes in steroid plasma titers are necessary for successful reproduction in all vertebrates. Gonadal steroidogenesis of the most intensively cultured teleost species in North America, the channel catfish (Ictalurus punctatus), is poorly understood so a year-long study was conducted to investigate seasonal changes in ovarian steroidogenesis. Incubations of ovarian tissue were conducted monthly with [3H]pregnenolone and the medium was analyzed by high-performance liquid chromatography (HPLC) with radioactivity detection. The suite of steroids produced by the catfish ovary included the expected sex steroids (estradiol and testosterone) and 18 additional ovarian metabolites, including five steroids that have yet to be identified. Androstenedione, 20beta-dihydroprogesterone, 5|P-dihydrotestosterone, estriol, 11beta-hydroxyandrostenedione, 17-hydroxypregnenolone, 17-hydroxyprogesterone, 11beta-hydroxytestosterone, and progesterone were characterized by a combination of HPLC and thin-layer chromatography. Two of the most abundant steroids were isolated and analyzed by gas chromatography coupled with mass spectrometry (GC-MS). One of the steroids, 7alpha-hydroxypregnenolone (7P5), is a novel steroid in teleosts and was produced late in vitellogenic growth of the oocyte. Evidence suggests that the enzyme responsible for converting pregnenolone to 7P5, 7alpha-hydroxylase, is a cytochrome P450. The second abundant steroid metabolite was partially characterized by GC-MS as an hydroxylated form of 17-hydroxy-pregnenolone (chi,17P5). This steroid was most abundant when the ovary was regressed and during early vitellogenesis and rapidly decreased prior to spawning. In mammals, 7P5 has been identified as an important neurosteroid; however, the reproductive significance of 7P5 and chi,17P5 in catfish is unknown.