Insulin release from the perifused isolated rat langerhans islets under a slow-rise glucose stimulation.

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Abstract
The dynamics of insulin release from perifused rat Langerhans islets was investigated under slow-rise and square-wave stimulation by glucose. Every dose response curve showed a sigmoidal profile, in which the threshold of glucose was around 4.2 mM. The Km values of dose response curves were similar each other under a slow-rise and square-wave stimulation by glucose. Since a rise of gradient level from 0.10 to 0.22 mM/min did not alter the dose response curve, the profile of insulin release in response to slowly rising glucose was not due to a lag time in insulin release but dependent on an absolute change of glucose level. The stimulation by rapid change of the glucose level with 2.80 mM/min of gradient level caused an insulin releasing profile similar to that caused by square-wave stimulation. Consequently, it was suggested that the insulin release under a slow-rise stimulation by glucose at gradient levels around 0.10-0.22 mM/min was more physiologic. This stimulation method is an easily available procedure for preparing an accurate dose-response relationship between the rate of insulin released and the concentration of glucose.