Ultrastructural localization of a fragment (16K) of the common precursor for adrenocorticotropin (ACTH) and beta-lipotropin (beta-LPH) in the rat hypothalamus.

With an antiserum to a fragment (16K) of the 31K common precursor for both adrenocorticotropin (ACTH) and beta-lipotropin (beta-LPH), the immunohistochemical localization of this 16K fragment was performed in the rat hypothalamus. At light microscopic level, 16K fragment was detected in the same neuronal cell bodies which also contain ACTH in the arcuate nucleus. Using serial thin sections for immunoelectron microscopy, it has been possible to demonstrate that 16K fragment and ACTH are present not only in the same cell bodies and fibers but also in the same dense core vesicles. These results indicated that in the central nervous system ACTH is originating from the 31K common precursor and that the active peptides (ACTH and endorphins) are stored in the same vesicles which also contain the common precursor and/or its fragment(s).