Metabolic Studies Following the Oral Ingestion of Different Doses of Glucose

Oral glucose tolerance tests were performed with variable glucose loads (30 gm., 50 gm., 100 gm., 200 gm., 300 gm.) in groups of healthy subjects. The concentrations of blood glucose, serum insulin and free fatty acids were measured in venous blood. Blood glucose concentration was also determined in capillary and arterial blood. The differences in glucose concentrations between capillary and venous blood were as high as 40 mg./lOO ml. The magnitude of the differences was related both to the time of determination and to the glucose load. One hundred and twenty minutes after beginning the tests there were little differences between the glucose concentration in capillary blood and in venous blood after doses of 30 or 50 gm. glucose. With larger doses of glucose higher values than the pretest values were still found in capillary blood but not in venous blood at the same time and also 180 min. after beginning the tests. Also, in contrast to the findings with doses of 30 or 50 gm. glucose, serum insulin levels were still elevated at 120 minutes after the higher glucose loads. The high values of serum insulin (70 to 90 μU./ml.) and the concentration differences between capillary and venous blood are explained best by the secretion of biologically active insulin because of a continual intestinal absorption of glucose. This confirms the assumption that the secretion of insulin is obviously not only stimulated by the actual blood glucose concentration but also by intestinal absorption of glucose. This mechanism is important in the oral glucose tolerance test because only 120 minutes after a load of 100 gm. glucose there is a continuous insulin secretion.