Abstract
OHNEDA, A., SAKAI, T., KOBAYASHI, T. and NIHEI, J. Insulin and C-Peptide in Plasma and Tumor of Insulinoma Patients. Tohoku J. exp. Med., 1983, 139 (1), 73-81 - In order to elucidate the heterogeneity in insulin secretion and insulin content of insulinoma tumor, insulin (IRI) and C-peptide (CPR) in plasma and tumor were studied in 11 patients with insulinoma and 14 healthy controls. The fasting levels of plasma IRI and CPR were significantly elevated in insulinoma as compared to the normal controls. The molar ratio of CPR/IRI was markedly decreased in patients with insulinoma, indicating higher increase in plasma IRI than CPR. Exaggerated responses of plasma IRI and CPR to glucose load were observed in insulinoma patients. Insulinoma patients revealed a gradual rise of plasma IRI and CPR in response to glucagon. Furthermore, the patterns of plasma IRI and CPR were extremely deviated from normal in the patients. The content of biologically measured insulin in the tumor tissue was increased in all the insulinoma patients. In contrast, immunoreactive insulin and C-peptide in the tumor scattered widely, indicating a dissociation between biological and immunological activity of insulin in the tumor. Chromatography of C-peptide extracted from the tumor elicited 2 parts with different molecular weight in addition to the part corresponding to the authentic C-peptide. From the present study, it is concluded that, although insulin secretion was exaggerated in the basal state as well as after stimuli, its regulation is abnormal in insulinoma. Furthermore, heterogeneity in biosynthesis and secretion of insulin in insulinoma was suggested by the results obtained from insulin content in the tumor and chromatography of C-peptide extracted from the tumors.
