We previously investigated the serum immunoreactive insulin response in diabetics with and without diabetic retinopathy. This prompted us to study the relationship between the response of immunoreactive insulin and the development of diabetic retinopathy. A 100g oral glucose tolerance test was performed in 58 cases where the grade of diabetic retinopathy was Scott III a or Scott III b at the time of well controlled diabetes. They still maintained good control of diabetes for one year thereafter. The responses of blood glucose and immunoreactive insulin to 100g oral glucose loading were compared between the groups with and without development of diabetic retinopathy during the one year observation period. The results is obtained were follows.
1) The blood glucose levels after glucose loading in patients with further development of diabetic retinopathy were higher than the levels in patients without development of diabetic retinopathy. A significant difference was found at the 2-hr point after glucose loading. The response of serum immunoreactive insulin after glucose loading was lower in the former than in the latter patients.
2) The ΔIRI/ΔBS ratio at 30 min after glucose loading in the patients with further development of diabetic retinopathy was lower than that in those without development of diabetic retinopathy. The proportion of patients whose ΔIRI/ΔIBS ratio at 30 min after glucose loading was less than 0.1 was 100% in the patients with development of diabetic retinopathy and 31.6% in the patients without development of diabetic retinopathy.
3) The ΣIRI/ΣBs ratio after glucose loading in the group with progression of diabetic retinopathy was lower than that in the group without progression of diabetic retinopathy. The proportion of patients whose ΣIRI/ΣBS ratio was less than 0.1 was significantly higher in the former than in the latter group.