Mammary Nucleic Acid, Hydroxyproline, and Hexosamine of Pregnant Rats during Lactation and Post-Lactational Involution1,2

Abstract

Early stages of concurrent pregnancy during lactation had relatively little effect on lactational performance (litter weight gain), deoxyribonucleic acid (cell numbers), ribonucleic acid (protein synthetic acivity), hydroxyproline (collagen), and hexosamine (ground substance) content of the mammary glands of rats. However, during advanced stages of pregnancy, litter weight gains were depressed. This decreased laetational performance was associated with reduced mammary deoxyribonucleic acid, ribonucleic acid, and hydroxyproline, but not hexosamine content.Concurrent pregnancy during the early stages of post-lactational involution (dry period) retarded but did not prevent marked declines in the biochemical parameters. During the dry period of concurrently pregnant rats, minimum values of deoxyribonucleic acid, ribonucleic acid, hydroxyproline, and hexosamine were reached at pregnancy stages of 12, 16, 16, and 20 days, respectively. Increases in these biochemical constituents during the remainder of the dry period concurrent with gestation only partially replaced the losses which had occurred in the early dry period. Therefore, the rats entered their second lactation with less nucleic acid, hydroxyproline, and hexosamine than found at the time of weaning in the first lactation. It is concluded that despite concurrent pregnancy even in very short dry periods, involution of the mammary gland occurs.