[Ultrastructural changes in the mammary glands of white rats during the estrus cycle]

Secretory granules of milk protein were found in the apical cytoplasm of some ductal cells in the mammary gland of non-lactating albino rats. During the estrous period, the diestrous phase, the number of "coated" vesicles increased essentially. Some of the "coated" vesicles contained secretory granules and granular debris. The functional relationship of the "coated" vesicles to lysosomes and to some other cytoplasmic structures is discussed. The results suggest that during the estrous phase formation and release of secretory products prevail, whereas at the diestrous the process of their removal and destruction is predominant.