Steroid Hormone Transformations by Endocrine Organs from Pregnant Mammals. I. Estrogen Biosynthesis by Mammalian Placental Preparationsin Vitro1

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Abstract
Placental preparations from sheep, cow, horse and sow have been shown to convert dehydro-epiandrosterone-7[alpha]-H3 and androstenedione-4-C14 to radioactive estrogens in vitro. In each case the extent of conversion was higher following incubation of the C19 substrates with a purified microsomal preparation. Cow placental preparations were able to synthesize radioactive estrogen from dehydroepiandrosterone, but only when a purified microsomal preparation was used could synthesis from androstenedione be demonstrated. No identifiable radioactive estrogen was demonstrated following incubation of rabbit and guinea pig placental preparations. In cases in which estrogen synthesis was demonstrated, both estrone and estradiol-17[beta] were identified in the estrogen fractions; in addition, estradiol-17[alpha] was identified in estrogen fractions from sheep and cow placental incubations. The ability ofplacental preparations from each of these species (except the guinea pig, which was not studied) to convert pregnenolone-7[alpha]-H3 or progesterone-4-C14 to radioactive estrogen could not be demonstrated. The data demonstrate the presence of both aromatizing enzyme systems and 17-ol-dehydro genase systems in placentae of sheep, cow, horse and sow, while 17,20-desmolase activity appears to be lacking in all the placentae studied. The significance of these results in relation to the endocrine activity of the mammalian placenta is discussed.

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