Adrenocorticotropin immunoreactivity is contained within presumptive endocytotic vesicles of rat Brunner's gland cells.

Using an immunofluorescence microscopic staining technique, adrenocorticotropin (ACTH)-stained myenteric plexus perikarya and nerve fibers as well as ACTH-immunoreactive submucous plexus nerve processes were revealed in the rat duodenum. However, ACTH-immunostained cells were also seen in Bunner's glands. In immunoelectron microscopic experiments could be demonstrated that the ACTH-immunoreactivity was contained within presumptive endocytotic vesicles of these cells. The ACTH-positive vesicles had a mean diameter of 270 nm. The ACTH-peroxidase anti-peroxidase (PAP) complex (mean diameter 50 nm) was located on the inner surface of the vesicle. At light microscopic level, ACTH-immunofluorescent nerve fibers were in close association with these ACTH-stained Brunner's gland cells. These findings might indicate that ACTH influences both the quality and quantity of the mucous produced by Brunner's gland cells.