A quantitative histotopologic analysis of the variation in lobulo‐alveolar mitotic activity in the Lewis/Mai rat mammary gland during the estrous cycle

Abstract

AbstractQuantitative microscopic techniques were employed to determine relative mitotic activity of lobulo‐alveolar tissue in thick sections obtained from the inguinal mammary glands of colchicine‐treated post‐pubertal Lewis/Mai rats sacrificed at different phases of the estrous cycle. It was found that the magnitude of lobulo‐alveolar cell mitotic activity and the proportion of the lobulo‐alveolar tissue with mitotic activity undergo significant fluctuations during the estrous cycle. The frequency distribution of mitotic activity in lobulo‐alveolar tissue was different and heterogenous at each phase of the estrous cycle. The frequency distribution of nuclei in lobulo‐alveolar tissue during the estrous cycle showed only minor variations and could not explain the variation in mitotic activity. Similarly, no morphological differences were observed in the mammary gland which could account for the variation observed in mitotic activity.It was concluded that the variation in mitotic activity of lobulo‐alveolar tissue is probably related to alterations in the generation time of lobulo‐alveolar cells imposed by cyclical variation in ovarian hormones during the estrous cycle.