Regulation of mammary nucleic acid content by various suckling intensities

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Abstract
The influence of 2, 4, or 6 suckling pups on DNA, RNA, and RNA/DNA of 6 abdominal-inguinal mammary glands of rats was determined at various stages of lactation. No increase in DNA was observed in rats suckling 2 pups per 6 glands after day 4, whereas DNA of rats suckling 4 pups/6 glands increased progressively until day 12. DNA of rats suckling 6 pups/6 glands increased 108% between days 1 and 16. DNA declined in all suckling intensities at days 20 and 24. Within each suckling intensity RNA and RNA/DNA increased until the 16th-20th days, then rapidly declined. Within each stage of lactation, the higher suckling intensities produced correspondingly higher RNA and RNA/DNA values, suggesting that cells produced during lactation were functional. In a 2nd experiment, progressive increases in suckling stimuli with maintenance of a constant pup-to-gland ratio did not promote increased nucleic acid synthesis. Nucleic acid losses in teat-ligated glands were partially retarded, but not quantitatively prevented, by increasing the suckling intensity from 1 to 3 pups between days 3 and 16 of lactation. Total RNA and DNA were highly correlated with litter weight gain (r > 0.93 and 0.85, respectively).