Uniphasic Insulin-secretory Response in the Pancreatic Vein of Dogs After an Enteric Glucose Load

The insulin secretory response to an enteric glucose load was measured in 11 dogs after intrajejunal instillation of a 25 per cent glucose solution (1.75 gm./kg.) in five minutes. Insulin outflow rate was measured every minute for 10 minutes, then at increasing intervals through 60 minutes. Starting at two minutes after onset of glucose loading, mean arterial plasma glucose rose steadily throughout the hour. This was paralleled by a similarly progressive rise in mean pancreatic venous plasma insulin output starting at seven minutes and peaking at 50 minutes, despite partial masking by a simultaneous fall in pancreatic venous plasma flow rate after the fourth minute. The data indicate that the normal insulin response to an enterically administered glucose stimulus is a smoothly rising uniphasic one, in contrast to the typical biphasic insulin response to a “square-wave” intravenous glucose stimulus.