Coated vesicles in the rat anterior pituitary gland.

Ultrastructural documentation of the formation of coated vesicles in prolactin cells of the rat anterior pituitary gland is presented. Coated vesicles were observed forming from the secretory granular membrane in the Golgi area and between the Golgi complex and the plasmalemma. They were also found budding off the membrane lining the exocytotic pocket. Following peroxidase reaction product could be seen forming from the membrane of the exocytotic pocket and adjacent to it. These vesicles were found in transit towards the Golgi area or within lysosomes. It is proposed that these coated vesicles are important for membrane conservation and that this is occurring in developing secretory granules near the Golgi complex, in more mature secretory granules and at the level of the plasmalemma during exocytosis.