[Changes in estrone and estradiol synthesis in fetal and newborn rats]

The question was approached whether estradiol synthesis by the rat ovary gained in importance with age relatively to estrone synthesis, which predominated largely in the 20-day-old fetus. Three stages were investigated, i.e. fetal stage 21 days and stages 2 and 7 days after birth. Ovaries were cultured in vitro in the presence of various radioactive androgens, and the conversion percentages into estrone (E1) and estradiol (E2) were determined by double isotopic dilution combined with recrystallization to constant specific activity. Insignificant in the 21-day-old fetus (E1/E2 ratio = 40), estradiol synthesis increased relatively to estrone synthesis in the 2-day-old neonate and still more at the stage of 7 days (E1/E2 ratio = 3). FSH had no effect on estrogen synthesis at the 3 stages investigated.