Diagnostic value of intravenous glucagon test in insulinoma.

The intravenous glucagon test was performed in 11 patients with insulinoma and the diagnostic significance of the test was studied in comparison with the glucose test, the tolbutamide test and the arginine test. The curves of plasma insulin following the intravenous administration of glucagon were markedly different and strange in those patients with insulinoma compared with the normal controls. The maximal levels of plasma insulin ranged from 85 to 400 muU/ml, exceeding the normal range in 10 out of 11 patients, or 91%. Increased levels in the maximal plasma insulin were observed in 63%, 100% and 56% through the glucose test, the tolbutamide test and the arginine test, respectively. The distribution of the insulin areas, calculated from the insulin curves during these tests, was shown to be similar to that of the maximal levels of plasma insulin. There was no significant correlations between the maximal levels of plasma insulin in the glucagon test and the glucose test, the tolbutamide test or the arginine test. The present experiment demonstrated that the intravenous glucagon test, next to the tolbutamide test, caused a large increase in plasma insulin, and therefore, that this test is one of the most useful tools among the provocation tests, for the diagnosis of insulinoma.

Plasma glucagon-like immunoreactivity (GLI) in dogs.

Gut glucagon-like immunoreactivity (GLI) was extracted from plasma of dogs and was compared for its molecular size and insulin releasing activity with GLI present in the intestine. Plasma was obtained from the portal vein of dogs, of which the pancreas was removed as rapidly as possible during the glucose administration into the intestine. Plasma GLI of intestinal origin was extracted by a modification of Kenny's method. The amount of GLI extractable from plasma in each dog ranged from 4.30 to 25.74 ng. The extract of plasma during glucose absorption was observed to have two peaks on gel filtration, corresponding to Peak I and Peak II of GLI extracted from the gastrointestinal tract. The intrapancreatic infusion of the Peak II GLI extractable from plasma promoted remarkable insulin release in dogs, like pancreatic glucagon. In contrast, the Peak I GLI from plasma caused an equivocal rise of insulin in the pancreatic vein. It is concluded from the experiment that gut GLI extracted from plasma shows the same elution pattern on gel filtration and the same insulin releasing activity as GLI extractable from the gut.

Heterogeneity of extractable gut glucagon-like immunoreactivity (GLI) and its lipolytic activity.

Gut glucagon-like immunoreactivity (GLI) was extracted from the mucosa of the canine intestine and was separated into two peaks by gel filtration; Peak I (7,000 daltons) and Peak II (3,500 daltons). These two peaks were purified by means of affinity chromatography using an anti-glucagon antibody as a ligand substance. These purified gut GLIs were not composed of single component, when applied to ion exchange chromatography. These partially purified Peak I and Peak II showed lipolytic activities, though very weak in potency, in vitro on the rat fat tissue at pharmacologically high concentration (5 ng eq/ml in final). It was concluded that gut GLI, even though purified, showed heterogeneity and that gut GLI revealed lipolytic activity although weak in potency compared with pancreatic glucagon.