Portal, hepatic and peripheral insulin immunoreactive substances before and after removal of an insulinoma.

Plasma insulin immunoreactivity (IRI) results from high molecular weight substances with insulin immunoreactivity (HWIRI), proinsulin (PI) and insulin (I). Their respective concentrations and percentages of IRI were determined preoperatively in the hepatic and peripheral circulations and after surgery in the latter two and in the portal circulation in a patient with a pancreatic adenoma. Removal of the insulinoma resulted in a highly significant reduction of PI concentration in the hepatic (from 16.2 +/- 1.9 microU/ml to 7.3 +/- 0.8 microU/ml) and in the peripheral (from 24.0 +/- 2.0 microU/ml to 9.2 +/- 1.2 micro U/ml) venous systems. Similarly, I concentration decreased in the hepatic (from 36.9 +/- 3.4 microU/ml to 28.0 +/- 1.0 microU/ml) and peripheral (from 33.8 +/- 3.4 microU/ml to 19.8 +/- 2.0 microU/ml) venous systems. HWIRI concentration decreased in the hepatic venous system (from 6.9 +/- 0.8 microU/ml, to 4.8 +/- 0.6 microU/ml), but the decrease in the peripheral venous system (from 9.7 +/- 1.4 microU/ml to 8.2 +/- 1.2 microU/ml) was not significant. It was found that the concentration of I virtually was the same in hepatic and peripheral blood prior to operation in contrast to a decrease seen after the operation. This indicates that the hyperinsulinemia caused primarily by the autonomous hypersecretion of the insulinoma was amplified by a decreased degradation of insulin by the liver and kidney. Our results also indicate that HWIRI was found with the highest concentration in the peripheral blood independently of the adenoma.