The rate of estrone production by mouse blastocysts increases with estradiol-17 beta concentration in medium

Following the finding of 17 beta-hydroxysteroid dehydrogenase activity in mouse blastocysts, the present study examined the relation of estrone (E1) production rate to estradiol-17 beta (E2) concentration in the medium. When Day 5 blastocysts were cultured in 107-6,860 ng E2/ml medium, the amount of E1 formed during the first 5 hours (y) was found to increase linearly with the logarithm of E2 concentration (x), as represented by the equation y = 2,161x - 3,947. However, there was a sharp decline during the next 5 hours of culture except for the 107 ng E2 culture. The E1 production then remained steady for up to 46-58 hours. There was a tendency for further decline during the 46-70-hour period. The results indicate that (1) E2 may be metabolized to E1 and, probably, another unknown steroid; (2) E1 production rate is E2-dose dependent; and (3) the blastocyst possesses the enzymatic capability to change the steroid milieu to suit its own needs and/or to cause local effects in the uterus for its proper implantation.