The ultrastructure of mast cells in the uterus throughout the normal menstrual cycle and the postmenopause.

During the menstrual cycle a gradation in mast cell granule ultrastructure was observed from the functional endometrium towards the myometrium of the uterus. Mast cells with particulate granules were present in the functional endometrium and those with granules containing identifiable scrolls in the basal layer of the endometrium and in the myometrium; mast cells containing very electron-dense granules were present in the deeper layers of the myometrium. The secretory activity of mast cells throughout the menstrual cycle is described. Mast cell secretion was observed to a lesser extent in the postmenopausal uterus. Mast cells with particulate granules were absent in the postmenopausal uterus and many very electron-dense granules were observed in mast cells in the myometrium.