1. An index of capillary permeability was obtained by measuring the ratio of the clearance rate of 77Br to that of 133Xe in the anterior tibial muscle, after a short period of maximal ischaemic exercise.

2. Seventeen control subjects and thirty-two maturity-onset, non-insulin-treated diabetic subjects, aged 60 years or less, were studied. Short glucose tolerance tests were performed in the diabetic subjects, during which blood sugar and serum insulin concentrations were estimated.

3. The 77Br/133Xe clearance ratio was increased in the diabetic subjects compared with the control subjects. In the diabetic subjects, there was an inverse correlation between the insulin at 60 min after glucose and the 77Br/133Xe clearance ratio. There was also a direct correlation between the 77Br/133Xe clearance ratio and the age of the patient in the diabetic group but not in the control group.

4. The results demonstrate that a reduced insulin response to oral glucose is associated with increased capillary permeability and may play a role in the development of microangiopathy.

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