Differences in Molecular Heterogeneity of Glucagon-Like Immunoreactivity in Plasma and Liver Metastases of a Patient with Alpha-Cell Tumor^*

Summary

In the present study we characterized and compared the different molecular forms of glucagon-like immunoreactivity in extracts of peripheral plasma and hepatic metastases of a patient with pancreatic alpha-cell tumor. Plasma and tissue extracts were chromatographed on Sephadex G-50 columns. Immunoreactivity in the eluting fractions was assayed with an anti-glucagon antiserum that specifically recognizes the C-terminal region of the pancreas glucagon molecule. Total plasma glucagon-like immunoreactivity prior to surgery was 26.64 nmol/1 and consisted of four peaks of immunoreactivity of apparent 9,000 mol wt, 5,800—5,400 mol wt, and 4,000 mol wt. Total glucagon-like immunoreactivity extracted from the hepatic metastasis was 47.41 nmol/g wet weight and eluted as two major peaks of immunoreactivity as follows: peak I, mol wt 3,800, corresponding to “true” 3,500 mol wt glucagon; peak II, mol wt 1,400, probably consisted of glucagon degradation products. The results clearly demonstrated that both plasma and glucagon-like immunoreactivity extracted from hepatic metastases were heterogenous and comprised species corresponding not only to “true” glucagon but also to higher mol wt forms. The lack of higher mol wt forms of immunoreactivity in the hepatic metastases of the alpha-cell tumor suggests that this metastatic tumor tissue may contain an enzyme capable of converting the higher mol wt forms to smaller glucagon-like components whereas this degradative system seems to be defective in the primary tumor.

Key words

Glucagon Immunoreactivity - Alpha-Cell Tumor - Plasma - Liver Metastases - Gel Chromatography