Abstract
The effect of insulin on blood glucose in the rabbit after direct instillation in the small intestine has been investigated. Crystalline Insulin, (U.S.P. U-40), administration via catheters placed in the duodenum, jejunum and ileum did not cause hypoglycemia at doses up to 50 U/kg. Tolbutamide (100 mg/kg) produced a hypoglycemic response after oral and intestinal administration. The lack of response to insulin is believed to be due to the destruction of insulin by proteoly-tic enzymes of the gastrointestinal tract.