[Placental and fetal growth in the rabbit: influence and mechanism of action of ovarian hormones (author's transl)].

During the second half of gestation in normal rabbits, hormonal overdoses result in similar modifications of placental and fetal weights, as in castrated animals identically treated (fig. 1). Nucleic acid and protein assays show that hormonal mechanisms are very different for the maternal (table I) and fetal portions of the placenta (table II): progesterone alone promotes a hypertrophy of the fetal placenta and hyperplasia of the maternal placenta. Estradiol at physiological levels counteracts these effects. Moreover, progesterone (fig. 3) and estradiol (fig. 2) receptors are found only in the maternal placenta, although the fetal placental is the most sensitive to the hormonal environment.