Localization of corticotropin- and endorphin-related peptides in the intermediate lobe of the rat pituitary.

The question is examined whether alpha-melanocyte stimulating hormone (alpha-MSH), adrenocorticotropic hormone (ACTH), met-enkephalin and beta-endorphin are detectable by enzyme immunocytochemistry in the cells of the intermediate lobe (PI) of the rat pituitary. By applying antibodies against alpha-MSH, ACTH and beta-endorphin on light microscopic sections, intense immunostaining was found in all PI-cells. At the ultrastructural level, after treatment of consecutive serial sections with these three antibodies the immunoreactivity was localized in the same secretory granules. No specific metenkephalin immunoreactivity could be detected in the cells of the intermediate lobe.