The glucagonoma syndrome: stimulus-induced plasma responses of circulating glucagon components IRG9000 and IRG3500.

Plasma responses of the major immunoreactive glucagon (IRG) components have been investigated in a case of glucagonoma syndrome. Fasting plasma IRG was 4155 pg/ml. Gel chromatography of plasma revealed that 66% of immunoreactivity was present as IRG9000, while IRG3500 accounted for an additional 26%. The appearance in peripheral plasma of these two glucagon fractions was examined after administration of a number of compounds. IRG levels were clearly elevated after arginine and tolbutamide. Both calcium and calcitonin induced a biphasic rise of IRG, the increase being slower after calcium administration. Somatostatin suppressed plasma IRG levels. All tests induced changes in both IRG3500 and IRG9000. In general, relative changes were more pronounced in IRG3500 than in IRG9000, while absolute changes were greater in IRG9000. The shape of the response curves of IRG3500 and IRG9000 was quite similar after arginine, calcium and somatostatin. After tolbutamide the IRG9000 response was delayed as compared to the IRG3500 component. During the latter part of the calcitonin infusion, IRG9000 remained elevated while IRG3500 was back at its starting level.