Postovulatory decrease in estrogen production is caused by the diminished supply of aromatizable androgen to ovarian aromatase.

After administration of testosterone to immature rats which had ovulated after treatment with PMSG and hCG, a significant increase in ovarian content of estradiol-17 beta was observed. Together with our previous result on the immediate decrease in ovarian 17 alpha-hydroxylase and C-17-C-20 lyase after PMSG and hCG treatment, it is concluded that the drastic decrease in serum estradiol-17 beta after ovulation is caused by a shortage of supply of aromatizable androgen(s) to the ovarian aromatase, due to diminished activities of the above two enzymes.