Abstract
The technique involving use of unlabeled antibody and the peroxidase-antiperoxidase complex was used to identify the adrenocorticotropin (ACTH)-secreting cell in the anterior pituitary lobe of the rat and to localize ACTH in it electron microscopically in ultrathin sections. The ACTH cell is star-shaped, with processes extending around other cells, and contains secretory granules of a maximal diameter of 300 mµ arranged peripherally along the plasma membrane. Stain was observed on secretory granules, around them, in the Golgi complex and in rough endoplasmic reticulum. One day after adrenalectomy, the ACTH cell is degranulated and the staining intensity of its remaining granules and cytoplasm is decreased, suggesting release of ACTH stores. If cortisol is given 6 hr after adrenalectomy, 18 hr later the ACTH cells are well granulated and the granules stain more intensely than normal. In addition, staining around the granules and throughout the cytoplasm is more intense, suggesting that an early effect of cortisol is to block release of ACTH. Twenty-one days after adrenalectomy, the ACTH cells are greatly increased in numbers and have complex, tortuous processes filled with intensely stained secretory granules.