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Influence of the Placenta in Mammary Gland Growth

Animal Husbandry Research Division, USDA, Beltsville, Maryland

ABSTRACT

The role of the placenta in promoting mammary growth was investigated by comparing the extent of development in rats either under full placental influence (pregnant), under maternal placental influence only (deciduoma), or under no placental influence (pseudopregnant). During the first ten days following mating there was little difference in glands of the three groups of rats. Early growth of the mammae was rapid, with good arborization and extensive lobulation in all three groups. During the subsequent period, however, only the pregnant group continued to show progressive growth. The deciduoma rats maintained an intermediate level, but the pseudopregnant group declined steadily in the 10–21-day post-mating period.

Suspensions of rat placenta were not effective in causing greater mammary growth when injected into either the deciduoma or pseudopregnant groups.

The results indicate a mammotropic influence of artificial deciduoma, suggesting a similar role for the decidual tissue of the maternal placenta during pregnancy.