An Immunochemical and immunohistochemical study on pancreastatin-like immunoreactivity using synthetic peptides

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Abstract
Chemical synthesis of pancreastatin fragments (33-49), (39-49), (42-49) and (45-49) was carried out using a solid-phase synthesizer, and antisera were characterized. The synthetic pancreastatin (33-49) coupled with keyhole limpet hemocyanine (KLH) was used as immunogen and antibodies were produced in New Zealand white rabbits. One of the antisera, T-2602, which showed the highest titer, recognized the C-terminal region of pancreastatin and cross-reacted equally with both pancreastatin (33-49) and native pancreastatin, but not with other known peptide hormones. Gel-filtration analysis of aliquots of tissue homogenates revealed the existence of four major components of pancreastatin immunoreactivity which corresponded to the elution position for pancreastatin precursor (void volume), native pancreastatin, pancreastatin (33-49), and related small peptide fragment in porcine pancreas. Analysis of tissue homogenates from the porcine adrenal gland revealed a predominant large-molecular form and a small amount of native pancreastatin. The immunohistochemical study using the antiserum T-2602 showed widespread immunoreactivity in amine/peptide producing endocrine cells. Not only pancreatic islet cells but also gut endocrine cells and adrenal chromaffin cells showed intense immunoreactivity in their secretory granules. As this immunoreactivity precisely coincided with that for chromogranin A, it is suggested that pancreastatin is a peptide closely correlated with chromogranin A.