Nucleic acid content of mammary glands of lactating rats.

Abstract

Total mammary DNA per 100 g of body weight increased 9.8% from day 20 of pregnancy to day 1 of lactation and 25.9% from day 1 to day 4 of lactation. Ovariectomy on day of parturition had no influence on mammary hyperplasia during early lactation. On the basis of total DNA per 100 g of body weight maximum mammary development occurred on day 8 of lactation (11.51 mg) and 24.8% of mammary growth occurred during lactation. No significant decrease occurred in mammary DNA until after day 24 of lactation. With the onset of lactation total mammary RNA increased much more rapidly than did total mammary DNA. Maximum mammary RNA content was observed on day 21 of lactation (75.06 mg) after which it declined precipitously to day 28 of lactation (39.61 mg). Mammary gland RNA/DNA ratio increased rapidly when lactation was initiated (1.24), attained its maximum on day 21 of lactation (2.95) and then decreased to day 28 of lactation (1.96). It is suggested that RNA/DNA ratios, when plotted against stage of lactation, represent the normal lactation curve of the rat.