Immunoreactive adrenocorticotropic hormone (ACTH) in porcine gut and pancreas: Fact or artifact?

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Abstract
Immunocytochemical observations have suggested the presence of ACTH in endocrine cells of the gut and pancrease of several species. In the pig, ACTH immunoreactive cells are fairly numerous in the pancrease and colon, especially at the time of birth. The immunoreactive material was characterized by immunocytochemistry using an array of different ACTH antisera. Only 2 antisera, both raised against highly purified porcine ACTH, were capable of demonstrating cells in the porcine pancreas and colon; antisera raised against various ACTH fragments did not stain these cells. The immunoreactive cells in the pancreas were distinct from previously identified islet cells (.alpha., .beta. D and PP cells). Absorption controls using antigen-inactivated antisera did not display any staining. The immunoreaction persisted when synthetic human ACTH 1-39 or a combination of ACTH fragments were used for absorption. Radioimmunoanalysis failed to reveal ACTH in extracts of pancreas and colon in newborn and adult pigs. Thus, the ACTH-immunoreactive material in endocrine cells of porcine gut and pancreas is distinct from authentic ACTH. The staining probably reflects the presence of a 2nd antibody population, directed against a contaminant(s) in the preparation of ACTH used for immunization. The nature of this contaminant is unknown; it is not identical with any known pituitary peptide. Highly purified porcine ACTH apparently contains a contaminant(s) that gives rise to antibodies reacting with a unique population of endocrine cells in the porcine gut and pancreas. This contaminant probably resides in the ACTH/MSH cells in the pituitary. In the porcine gut and pancreas this contaminant or a chemically related compound, but not ACTH, is present in a special population of endocrine cells.