Abstract

PIP: Ultrastructural changes in the alveolar mammary cells and in the pituitary prolactin cells of lactating rats bearing local mammary estrogen implants are reported. The alveoli showed an early regression process, similar to the one observed after weaning. The findings show that the synthesis of milk is altered only to a minor extent, and the authors believe that the inhibiting effect on lactation caused by estrogen is primarily the result of a local action on the alveoli, which cannot empty their content. Thus, estrogen would affect the final stage of milk secretion. Further study is required to determine the exact time and place of estrogen action.