INVESTIGATION INTO THE POSSIBLE ROLE OF ANDROGENS IN THE INDUCTION OFHEPATIC VITELLOGENESIS IN THE EUROPEAN EEL - IN-VIVO AND IN-VITRO STUDIES

Changes in the levels of plasma vitellogenin (Vg), estradiol (E-2) and testosterone (T) were examined following gonadal development induced by carp gonadotropin treatment (cGTH) of freshwater female yellow and silver eels (Anguilla anguilla L.). The animals received injections of cGTH (250 mu g kg(-1) body weight) or saline vehicle three times a we ek, for 6 to 8 weeks. No effect of vehicle was observed. Steroidogenic activity of the ovary was stimulated by cGTH treatment as shown by th e increase in circulating steroid levels in both stages. However, the responses of T, E-2 and Vg differed according to the stage of developm ent of eels. At the yellow stage, the initial steroid plasma levels we re undetectable (< 0.01 ng ml(-1)) before treatment and ovarian steroi dogenic activity was slightly stimulated following cGTH treatment; ste roid levels reached their highest values after 3 weeks and 6 weeks of treatment for E-2 (0.62 +/- 0.13 ng ml(-1) and T (0.33 +/- 0.30 ng ml( -1)), respectively. The cGTH treatment slightly increased plasma Vg le vels (0.2 - 0.7 mu g ml(-1) during the experiment compared with the in itial values of the group. At the silver stage, the initial steroid le vels were detectable (0.7 ng ml(-1) for E-2 and 0.1 ng ml(-1) for T); cGTH treatment did not significantly increase plasma E-2 level which r emained at initial levels. Nevertheless, plasma T levels dramatically increased from 0.1 to 3 ng ml(-1) and peaked after 1 or 2 weeks of cGT H treatment; a rapid increase in plasma Vg levels occurred, reaching i ts highest value at 5 mg ml(-1) after 3 weeks of treatment. Thus, the steroid kinetic profiles in relation to the appearance of Vg in the pl asma following cGTH treatment was closely related to androgen levels a nd there was a strong vitellogenic response induced by chronic cGTH tr eatment. In order to test if androgens could be implicated in the vite llogenic response, we evaluated the potencies of various androgens (te stosterone and 5 alpha-androstane-3 beta,17 beta-diol) in vivo and in vitro, associated with E-2 to induce the production of Vg. lit vitro e xperiments showed that Vg synthesis was induced by high doses (10(-6) to 10(-5) M) of androgen in the eel. Tamoxifen totally inhibited the a ction of androgens suggesting that androgens were acting through bindi ng to the E-2 receptor. In vivo, androgens given alone at 50 mu g kg(- 1), 3 times a week for 1 months had no significant effect on plasma Vg levels. In addition, E-2-androgen cotreatment showed that the presenc e of androgen did not modify the vitellogenic response induced by E-2.