Adrenocorticotropin production by the intermediate lobe of the rat pituitary. An electron microscopic-immunohistochemical study.

Abstract

Adrenocorticotropin (ACTH) was localized in the intermediate lobes of normal rat pituitaries with unlabeled antibody and the soluble peroxidase-antiperoxidase complex at the electron microscopic level. All of the intermediate lobe cells (light and dark cells) stained positively for ACTH. Stain of varying intensity was found on secretory granules and vesicles. Structures which resembled rough endoplasmic reticulum stained where the secretory granules and vesicles were most numerous. No stain was on mitochondria, in nuclei, in cisternae and granules of Golgi complexes, or in rough endoplasmic reticulum where there were few secretory granules. There were distinct immunohistochemical differences between the pars intermedia and anterior lobe ACTH cells. In the ACTH cells of the anterior lobe, the Golgi complex and its granules stained strongly, but not at all in the pars intermedia cells. This suggests that ACTH may not be packaged or condensed in the Golgi region of the latter.