Quantitative determination of insulin output following an intravenous glucose tolerance test in the dog

Abstract

Nine dogs had 50 to 70% of their pancreas removed. The uncinate process with intact pancreatic branches of the inferior pancreaticoduodenal artery and vein was completely isolated. Blood was continuously collected from the superior pancreaticoduodenal vein, whose duodenal branches were clamped off as was also the inferior pancreaticoduodenal vein. The volume of blood collected was measured, timed, and analyzed for the concentration of plasma insulin activity by the mouse hemidiaphragm bioassay and by immunoassay. Mean fasting values were 11.4 ± 2.4 milliunits (bioassay) and 12.1 ± 3.8 milliunits (immunoassay) per kg body weight per h in native plasma respectively. The high amounts obtained by both methods are similar and match the daily insulin requirements per kilogram body weight of the depancreatized dog or man. Tolerance to glucose was decreased in four dogs because of their deprivation of endogenous insulin during the experiment. Insulin secretion rose in the first 5 min but showed a delayed greater peak around 1 h after the glucose injection. The total inflow of blood into the pancreatic remnant was determined with an electromagnetic flowmeter. After the injection of glucose the blood flow increased twofold, and corresponded in time to the peaks of insulin output. The outflow from the superior pancreaticoduodenal vein increased two to four times when its duodenal branch was unclamped, because of the increased inflow of intestinal blood. Five control dogs did not receive glucose. Their blood insulin levels did not rise. In these the pancreatic blood flow decreased gradually with a progressive loss of blood through continuous sampling, for 2 h.