Blood glucose regulation using an open-loop insulin delivery system in pancreatectomized dogs given glucose infusions. I. Portal square waves.

This study characterizes the glycaemic and insulin responses of a group of 5 anaesthetized dogs to a portal glucose infusion of 10 mg/kg/min before and after pancreatectomy. Insulin was administered intraportally to the pancreatectomized dogs according to a simple preprogrammed waveform composed of a constant basal rate of 0.35 +/- 0.02 mU/kg/min which was increased to 2.00 mU/kg/min at the time of the 60 minute glucose challenge. When this square waveform was applied the glycaemic response was similar to that seen in the normal controls in the baseline and challenge periods. Blood glucose concentration differed significantly (p less than 0.05) only from 20 to 100 minutes after the end of the challenge when it was higher by 20 +/- 1 mg/dl. Insulin levels were not significantly different from controls. It may be concluded that normoglycaemia and normoinsulinaemia can be maintained by a simple constant rate of portal insulin delivery while the blood glucose response to a glucose infusion can be ostensibly normalized without hyperinsulinaemia simply by enhancing insulin delivery during the challenge. The feasibility of this approach implies that with further development of the preprogrammed waveforms and with a greater understanding of their characteristics portable insulin delivery systems may be realized which accomodate more physiological challenges. The portal route for insulin delivery may however be necessary if peripheral hyperinsulinism is inappropriate.