Abstract
In rats, the influence of pregnancy, fetuses, fetal placentas and pseudopregnancy with and without deciduomas on mammary and uterine development (DNA content) and metabolism (RNA content) was studied. Mammary nucleic acid content increased throughout pregnancy. Removal of fetuses before midpregnancy, but not after, interfered with normal increases in mammary DNA and RNA content. Excision of fetal placentas caused mammary development to regress to nonpregnant control values. Mammary development during the first 12 days of pseudopregnancy was 29–33% less than that observed in 12-day pregnant rats. It is suggested that maternal hormones are the primary stimulant of mammary development during the first half of pregnancy. However, the fetal placentas commence to stimulate mammary development before midpregnancy, and they may be the primary limiting factor for mammary development during the second half of pregnancy. Uterine DNA increased 2.8-fold, whereas uterine RNA and weight increased 5.8- and 4.6-fold, resp...
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