Studies on the particulate components of rat mammary gland. 2. Changes in the levels of the nucleic acids of the mammary glands of rats during pregnancy, lactation and mammary involution

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Abstract
Changes in the total, and mitochondrial N, total RNA, mitochondrial RNA and DNA content of the rat mammary gland were studied at intervals during the lactation cycle. The total and the mitochondrial N of the gland rose similarly through pregnancy and lactation. RNA increased progressively from early pregnancy to late lactation and declined again during mammary involution. Parturition was accompanied by a rapid rise in the RNA of the mammary gland. The mitochondrial RNA rose during pregnancy, but reached a plateau by the 3d day of lactation which was maintained until mammary involution set in. The DNA of the gland increased during pregnancy. The DNA level doubled at parturition, then remained constant throughout lactation. Changes in the level of RNA are discussed in relation to the rate of protein synthesis in the gland. Evidence is adduced for an increase in the microsomal and submicrosomal fractions during lactation. The changes in DNA content of the mammary gland are discussed. They indicate that a wave of cell division occurs in the gland around the time of parturition.