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Collagen of Rat Mammary Glands During Post-Lactational Involution

Animal Science Research Division, USDA, Beltsville, Maryland 20705

ABSTRACT

Nucleic acid and collagen content of parenchymal and fat pad segments of mammary glands were determined on rats killed at Days 0, 5, 15, 30, and 60 post-weaning. By 5 days post-weaning, involution of the mammary gland parenchyma was accompanied by large and rapid decreases in nucleic acid (DNA and RNA) of the tissue. Conversely, DNA and RNA content of the fat pad segment increased following weaning. By the 15th day of involution, DNA and RNA in both the parenchyma and fat pad segments were similar to amounts in virgin animals.

Parenchymal hydroxyproline (collagen), on the other hand, did not decrease until the 15th day at which time it leveled off to amounts comparable to virgin controls (4.0 mg/100 g body wt). Fat pad hydroxyproline increased for 15 days following weaning reaching amounts in virgin mammary glands (1.6 mg/100 g body wt). The collagenous framework of the mammary gland involuted slowly compared to cell numbers but, nevertheless, reached amounts in virgin glands at about the same time as the nucleic acid components of the gland (15 days).