Normal Growth of Rat Mammary Glands During Pregnancy and Lactation.

Abstract

With deoxyribonucleic acid (DNA) as a measure of mammary gland growth in the rat, it was shown that there was a 41.5% increase between 18-20th day of pregnancy and day 5 of lactation. This increase occurred in spite of the fact that DNA/nucleus of lactating cells is reduced 42.8% in comparison with cells of pregnant animals. Increased total DNA for 6 abdominalinguinal glands/100 g body weight was maintained until day 21 of lactation. Animals ovariectomized on day 2 of lactation showed equal increases on day 14 of lactation. It is concluded that marked glandular proliferation occurs following parturition (5 to 10 days) which is not interfered with by ovariectomy. It is suggested that post-parturient mammary gland growth, instead of depending upon ovarian hormones, may be due to direct release of pituitary mammogen associated with release of oxytocin and lactogen by periodic nursing stimuli.