High plasma pancreastatinlike immunoreactivity in a patient with malignant insulinoma

High levels of pancreastatinlike immunoreactivity were detected in the plasma (2.9 pmol/ml, >200-fold the normal level), pancreas (2.9 nmol/g wet wt, > 450-fold the normal level), and liver (1.6 nmol/g wet wt) of a patient with pancreatic insulinoma with metastasis to the liver by a sensitive and specific radioimmunoassay for human pancreastatin. Antiserum was produced against the C-terminal fragment of human pancreastatin-(24–52), which was synthesized according to the sequence of human chromogranin A corresponding to that of pancreastatin. With the antiserum, intense immunocytochemical staining was detected in the tumors. Sephadex G-50 gel filtration showed that the tumors and plasma contained two molecular forms of pancreastatinlike immunoreactivity—a molecular form coeluted with synthetic human pancreastatin-52 and a larger molecular form (Mr ~ 12,000–15,000). The smaller form eluted in the same position as synthetic human pancreastatin-52 on reverse-phase high-performance liquid chromatography.