The relationship between the basal glucose concentration, glucose tolerance and peripheral glucose uptake has been studied in nonobese diabetic males not requiring insulin by determining forearm glucose uptake (FCU) during a 100 gm. oral glucose tolerance test (GTT) before and after carbohydrate restriction.
On a normal diet basal glucose concentrations were elevated and glucose tolerance was grossly impaired; the increment in FCU during the CTT (0 to 180 minutes) amounted to 52.8 mg./100 ml. forearm. After carbohydrate restriction basal glucose concentrations were reduced, the glucose tolerance curve was lowered and the increment in FCU rose to 76.5 mg./100 ml. forearm; glucose tolerance, however, expressed as the incremental area under the glucose tolerance curve (0 to 180 minutes), remained unchanged.
Serum insulin responses during the tests were low and uninfluenced by carbohydrate restriction. Blood lactate concentrations were increased by glucose loading before but not after carbohydrate restriction. FFA and β-hydroxybutyrate concentrations fell progressively after glucose loading while, conversely, acetoacetate concentrations were initially unchanged. During the GTT acetoacetate was taken up by the forearm while lactate and β-hydroxybutyrate were released.
In addition, the responses of three diabetics on a normal diet were compared with those of age-matched normal men; in each diabetic FGU was equal to or greater than that in the normal subjects, but nonetheless, the increment in glucose concentrations was several times greater.
The results suggest that in these patients with diabetes [1] the lowering of the glucose tolerance curve by carbohydrate restriction is not synonymous with an over-all improvement in tissue glucose disposal but is due primarily to a fall in the basal glucose concentration and [2] the impairment of glucose tolerance both before and after carbohydrate restriction is predominantly the result of a reduction in hepatic rather than peripheral glucose uptake.
