Histological Changes in the Pregnant, Lactating and Involuting Mammary Gland of the Guinea Pig

The histological changes of mammary glands ofguinea pigs during mid and late pregnancy, 1 day after parturition, peak lactation and 2, 3, 4, 8 and 12 days after weaning were studied. Rapid growth of the glandular tzssue occurred towards late pregnancy and was completed by peak lactation. Plasma cells occurred in large numbers in the interalveolar connective tzssue during the period between mid-pregnancy and lactation. Mammary involution was an autolytic process aided by the action of macrophages accompanied by shrunken alveoli and increased interalveolar connective tzssue. Thzs feature was evident at 3 days after weaning which began from the perzphery of the glands. The number of macrophages were abundant in the connective tzssue and alveolar and ductal lumina. By day 8, the alveoli were no longer recognisable and at 12 days after weaning only remnants ofductules and alveoli were present.