Seasonal variation in tissue estrogen-2/4-hydroxylases (EH) and in vitro effects of steroids on ovarian EH activity in the catfish Heteropneustes fossilis

▶ EH activity was the highest in microsomes of liver >brain >ovary. ▶ The enzyme showed seasonal changes with the highest activity in spawning phase. ▶ In oocyte follicles, strong activity was elicited by the follicular layer. ▶ Steroids showed varying degree of suppressive effects, P4 and 2-hydroxy-E2 were highly effective.