Insulin responses to intravenous fructose and glucose were measured in 15 patients with maturity-onset diabetes mellitus. In eight patients given fructose first the insulin responses to fructose and glucose were similar. In seven patients given glucose first the insulin response to subsequently infused fructose was significantly greater than to glucose. Multiple regression analysis showed that the ratio of the fructose to glucose insulin response, assessed by area under the insulin serum concentration-time curve (F/G ratio) in individual patients, correlated most closely with prefructose infusion plasma glucose. Similar analysis, applied to results in 27 normal subjects, showed that the most important determinant of the insulin response to fructose in this group also was the immediate prefructose infusion plasma glucose. Thus in diabetics, as in normal controls, the response of the beta cell to intravenous fructose appears to be sensitively set by the ambient plasma glucose concentration at the onset of fructose infusion.

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