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), administered 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 proteolytic enzymes of the gastrointestinal tract.

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