Comparison of Effects of Estetrol and Tamoxifen with Those of Estriol and Estradiol on the Immature Rat Uterus1

Abstract
The estrogenic effects on this immature rat uterus of estetrol [1,3,5(10)-estratriene-3,15α, 16α, 17β-tetrol] (E4), a major metabolite of placental estrogens in the human fetus, and of tamoxifen (TAM), an antiestrogen, were compared with those of estradiol (E2) and estriol (E3). The compounds were injected s.c. daily, for 3 days, into 22- or 23-day-old Sprague-Dawley rats at a dose of 50 µg/100 g BW of E4 or TAM, and 1 µg/100 g BW of E2 or E3. Tissue was collected 24 to 27 h after the third injection.