The Glycogenolytic Activity of Immunoreactive Pancreatic Glucagon in Plasma

Conclusions concerning the physiologic role of pancreatic glucagon in health and its contribution to disorders of carbohydrate metabolism, such as diabetes mellitus, are based entirely on measurements of plasma glucagon by radioimmunoassay. The changes in plasma immunoreactive glucagon can have the metabolic and clinical significance which has been implied, only if the glucagon detected by immunoassay has biological activity. The present study was designed to determine if a relationship between the immunoassayable glucagon and glycogenolytic activity of plasma could be demonstrated. Plasma specimens obtained from normal and diabetic subjects under widely varying circumstances of alpha cell activity were extracted by a modification of the Kenny technique and the recovery of immunoreactive glucagon was calculated. Glycogenolytic activity of each extract was determined by perfusion in the Mortimore rat liver system, modified so as to detect as little as 1 ng of crystalline glucagon.A significant correlation between the calculated quantity of immunoreactive glucagon and the glycogenolytic activity of plasma extracts was observed for both normal and diabetic subjects. Most of the glycogenolytic activity was abolished by incubating the extract with antiglucagon serum. It was concluded that the glycogenolytic activity of extractable glucagon is proportional to its immunoreactivity as calculated from its original concentration in plasma. This would tend to support the view that all or most of the immunoreactive glucagon of plasma is biologically active.