The immunolocalization of ACTH and alpha MSH in human and rat pituitaries

Abstract

Human and rat pituitaries were investigated immunohistochemically for ACTH and alpha MSH activity by means of the enzyme-labeling technique. In rat pituitaries cells present in both the anterior and intermediate lobes were reactive with the anti-ACTH antibodies, the cells from the intermediate lobe were also reactive with anti-alpha MSH antibodies. In human pituitaries, ACTH-immunoreactivity was found in cells from the anterior lobe and cells invading the posterior lobe. In 5 out of 15 pituitaries ACTH-immunoreactive cells located at or invading the posterior lobe were also reactive with the anti-alpha MSH antibodies. It is concluded that the human pituitary cells that invade the posterior lobe represent a population which is at least immunohistochemically identical with the intermediate lobe cells of the rat. The ACTH-immunoreactivity of intermediate lobe cells may be explained by the presence of a corticotropin-like intermediate lobe peptide (CLIP) which has been suggested to be a prohormonal fragment of alpha MSH.