Insulin responsiveness of superficial forearm tissues in type 2 (non-insulin dependent) diabetes

Forearm perfusion studies were carried out to determine the responsiveness to insulin of the superficial forearm tissues in non-obese Type 2 (non-insulin-dependent) diabetics, and the interrelationships among plasma concentrations of glucose, insulin and non-esterified fatty acids (NEFA), tissue uptake of glucose and insulin and tissue release of NEFA. It was found that: (1) in normal subjects, uptake of glucose was dependent on glucose concentration. It was also dependent on insulin concentration in the range of 0-30 mU/l, but not over a wider range of insulin concentration (less than 66 mU/l), indicating that the insulin effect was maximal at approximately 30 mU/l. In contrast, glucose uptake in diabetics was independent of glucose concentration but dependent on insulin uptake over an insulin concentration range up to 140 mU/l; glucose uptake reached the same levels as in control subjects but only at higher concentration and higher uptake of insulin. (2) Insulin uptake was directly dependent on insulin concentration and the regression coefficients were very similar in the two groups. (3) NEFA concentration fell to comparable levels in the two groups of subjects in response to insulin. It is concluded that in Type 2 diabetes: (1) the superficial forearm tissues show decreased responsiveness to the stimulatory effect of both hyperglycaemia and hyperinsulinaemia on glucose utilization but the NEFA-lowering effect of insulin is undiminished, and (2) tissue uptake of insulin is normal, despite the decrease in receptor capacity that has been demonstrated by others.