Guinea Pig Mammary Gland Growth Changes in Weight, Nitrogen and Nucleic Acids.

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Abstract
The growth of guinea pig mammary glands during pregnancy, parturition, lactation and involution was measured using total weight, total nitrogen content, total DNA and RNA/DNA ratios as parameters of cellular changes. Only slight changes were found to occur during pregnancy. The rapid increase in total weight after parturition, correlated with the increase in total nitrogen and DNA, indicates that the observed growth is primarily a hyper-plastic process. Extensive hypertrophy of pre-existing cells as measured by increased RNA/DNA ratios occurs after the period of rapid prolifera-tive growth, thus the greatest cellular changes in guinea pig mammary glands occur immediately after parturition.