[Modulation of 17-alpha-hydroxy-20 beta-dihydroprogesterone or gonadotropic extract activity on the in vitro intrafollicular maturation of rainbow trout (Salmo gairdnerii) oocytes by various steroids lacking maturing activity].

The efficiency of 17 alpha-hydroxy-20 beta-dihydroprogesterone (17 alpha-20 beta Pg) or of a Trout pituitary gonadotropic extract to induce intrafollicular maturation of trout oocytes can be modulated by some steroids which do not present any direct maturing action: gonadotropic extract efficiency is lowered by estradiol and estrone, and enhanced by testosteron. As these steroids do not present a significant effect on 17 alpha-20 beta Pg induced maturation, their site of action may be located in the follicular tissues. The corticosteroids, particularly cortisol and cortisone enhance the maturing efficiency of gonadotropin and stimulate much more strongly the efficiency of 17 alpha-20 beta Pg. This suggests a direct effect on oocyte sensitivity to 17 alpha-20 beta Pg.