Ultrastructural localization of corticotropin, beta-lipotropin, and alpha- and beta-endorphin in the porcine anterior pituitary.

The peroxidase-antiperoxidase immunocytochemical technique was used to identify the ACTH/endorphin cells in the porcine pituitary at the ultrastructural level and to determine the precise subcellular localization of the pro-ACTH/endorphin fragments. The cells display different aspects: 1) large, regular shapes with numerous and large secretory granules; 2) small, irregular and angular shapes with small granules aligned along the periphery of the cell; and 3) intermediate forms. The presence of alpha- and beta-endorphin not only in the same cells but also in the same secretory granules that contain ACTH and beta-LPH clearly indicates that both the precursor or its fragments and the above-mentioned peptides are stored in the same granules and released simultaneously by the corticotropic cells. The presence of FSH in some corticotropic cells is also discussed.