Hypoglycemic reactions, induced by insulin (0.2 U./kg. intravenously), were studied in sixteen diabetic and twelve nondiabetic control subjects. The course of the reaction was monitored by continuous recording of the galvanic skin reflex (GSR) and by determination of the levels of blood glucose and free fatty acids (FFA) at 10, 20, 30, 60 and 120 minutes. Symptoms of reaction appeared in all of the controls at 32 ± 12 minutes after the insulin at a mean blood glucose level of 22 ± 7 mg. per 100 ml., and in the eleven of the diabetics at 70 ± 30 minutes and at a mean glucose level of 280 ± 192 mg. per 100 ml.

Onset of the insulin reaction was documented by a sudden drop in GSR which corresponded with the onset of symptoms. The GSR fell to a mean of 75 per cent of the baseline value and returned to the baseline thirty minutes later. All of the controls and nine of the diabetics showed the GSR response.

The GSR correlates well with symptoms of insulin reactions. Evidence of insulin reaction occurring in nine diabetic patients at high blood glucose levels is documented by GSR response.

Free fatty acids (FFA) in the plasma showed a more rapid return to baseline values in those subjects manifesting the quicker GSR response. The change in the GSR is a more sensitive though less specific measure of the homeostatic response to insulin than the change in the FFA.

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