Abstract
Ultrastructural changes in prolactin cells of the mouse anterior pituitary gland during the estrous cycle were investigated using a morphometric method with the electron microscope. The secretory granules are released by exocytosis and the exocytotic figures showed a large fluctuation in number during the estrous cycle, being adundant in proestrus and estrus, scarce in metestrus and diestrus in a ration of 7.5: 7.5: 1: 2, respectively. The length of the cell perimeter varied in a similar fashion. The volumes of cytoplasm, nucleus and cellorganelles also showed a similar variation throughout the estrous cycle, generally reaching the maximal level in proestrus and/or estrus, being smallest in metestrus and beginning to rise in diestrus. On the other hand, the frequency of exocytotic figures being open to the parenchymal basal lamina which delineated the pericapillary space were three-to five-fold over that of exocytotic figures being open to the intercellular space through every days of the estrous cycle. This suggests that an interaction between the cell membrane and the parenchymal basal lamina may play an important role in the mechanism of exocytosis.
