Nucleic Acid Content of Rat Mammary Gland Nuclei during Pregnancy, Lactation, and Involution

SummaryThe quantity of DNA per rat mammary gland nucleus was significantly lower during involution in comparison to pregnancy and lactation. Significant differences in both RNA and DNA contents per nucleus among glands occurred during pregnancy, lactation, and involution. Nuclear RNA contents and RNA, DNA ratios increased from pregnancy to lactation and then decreased during involution. A correlation of 0.47 was found between the litter weight at day 10 of lactation and the DNA content per nucleus. The presence of metabolic DNA and its relationship to protein synthesis in rat mammary gland is indicated. The efficiency of utilization of the available DNA template is suggested as the most meaningful interpretation of the RNA, DNA ratio. Sufficient evidence has been accumulated to reject the use of DNA per mammary gland as an index of the number of cells in the gland.The authors are grateful to Dr. Y. N. Sinha and Mr. D. M. Lawson for their interest and technical advice.