THE GLUCOSE METABOLISM IN THE ISLETS OF LANGERHANS. I. IN VITRO STUDIES OF THE FATE OF UNIFORMLY 14C-LABELLED GLUCOSE AND FRUCTOSE IN COTTUS QUADRICORNIS L

Abstract

ABSTRACT By the application of the radio-paperchromatography technique the fate of uniformly 14C-labelled glucose and fructose in the pancreatic islet tissue was studied in vitro. Islet tissue was taken from the teleost Cottus quadricornis L, after microscopical analyses had revealed that the »principal islets« in this species were suitable for biochemical research. For comparative purposes samples from the exocrine portion of the pancreas as well as from the brain and liver were also taken for incubation. There was a comparatively high rate of glucose utilization in the islet tissue, the corresponding values for the exocrine parenchyma and the liver being much lower. Of the different amino acids formed in the islets by conversion of the glucose in the incubation medium, alanine was found in largest amounts, followed by glutamine, proline, glutamic acid, aspartic acid and arginine. After incubation with fructose, there was a marked decrease in the rate of utilization as compared with glucose. In the latter case the only amino acids formed in measurable amounts in the islet tissue were alanine and proline. The islet tissue like other endocrine organs so far studied had its own characteristic distribution pattern for the amino acids formed from glucose. This conversion of glucose may perhaps be an important step in the specific function of the islet tissue in providing some of the amino acids necessary for hormone synthesis. Since the other tissues studied in Cottus quadricornis L resembled corresponding tissues in mammalian species, as regards the fate of glucose and fructose, it is probable that some of the observations on glucose and fructose metabolism in the islet tissue also have a more general application.