Abstract
Rat mast cells were examined by immunohistochemistry and radio-immunoassay with antisera to various regions of the prohormone procorticottopin (ACTH)/β-endorphin. These antisera revealed specific immunostaining in mast cells obtained from the peritoneal and thoraic cavities and in sections of rat tongue, mesenterium, and lung. Addition of the histamine liberator compound 48/80 to suspensions of peritoneal-thoracic mast cells produced a large increase in the level of ACTH and β-endorphin in the medium as measured by radio-immunoassay. Although the released material in each case produced a displacement curve parallel to that of the known peptide, this phenomenon was attributed to degradation of labelled hormone by an apparent protease released from mast cells. ACTH immunoreactivity was not detected in cell extracts obtained with boiling water or acetic acid. These data strongly emphasize the potential artifacts that can occur when immunoreactivity alone is in the criterion for determining the presence of peptide hormones in cells.