Timing of insulin delivery with meals.

In non-diabetics neural and/or gastrointestinal humoral factors cause anticipatory insulin release with meals. The importance of this mechanism was illustrated by administration of a standard meal to six insulin dependent diabetics on two occasions. Insulin was delivered intravenously by an "open-loop" (preprogrammed) insulin infusion system designed to simulate the normal insulin response to meals. On one occasion insulin delivery was delayed 15 minutes. This time approximates the physiology delay before blood glucose rises after the start of a meal. The delay resulted in significantly greater hyperglycaemia continuing over three hours, compared with the study in which insulin delivery increased coincident with the start of the meal. A mechanism for initiating early insulin release with meals would be a helpful addition to "closed-loop" insulin delivery systems, this being apparent in a further comparison made between performance of the open-loop and closed-loop systems. Moreover, the delayed insulin response seen in maturity onset diabetics is likely to be an important cause of persistent hyperglycaemia.