Involution of the Mammary Gland in Hamsters1

Nucleic acids were measured in mammary glands of hamsters after 5 or 10 days of involution. Litters were varied in size from six to one pup during a normal lactation which preceded the period of involution. DNA in the mammary glands varied directly with size of litter after 5 days of involution. However, no relationship between DNA and litter size was noted after 10 days of involution. RNA levels in the glands were lower than but paralleled the DNA changes. The data suggest that involution of the mammary glands of hamsters is virtually complete after 10 days, regardless of the level of lactation prior to the involutionary period.