REVERSIBILITY OF RETINAL FLOW ABNORMALITIES IS DISEASE-DURATION DEPENDENT IN DIABETIC RATS

Decreased retinal blood flow has been measured in streptozotocin (STZ) -induced diabetes of 1 week's duration, and primary insulin interventi on was effective in maintaining normal retinal blood flow in diabetic rats. Retinal blood-flow abnormalities precede clinical diabetic retin opathy in both diabetic animals and patients. An important characteris tic of diabetic retinopathy is the difficulty of reversibility once it has been established. Because altered retinal hemodynamics is a possi ble marker of early diabetic retinopathy, me investigated in this stud y whether retinal blood-flow changes in rats can be normalized by seco ndary insulin intervention following short and chronic periods of untr eated STZ-induced diabetes. Subcutaneous insulin pumps were placed int o diabetic rats for 1 meek after 1 week of diabetes (a-week group) and after 3 weeks of diabetes (4-week group). Retinal circulatory paramet ers were determined using image analysis of video fluorescein angiogra m recordings. For the a-week group, retinal blood flow was significant ly (P < 0.05) reduced in the untreated diabetic rats compared with non diabetic and insulin-treated diabetic rats (80.6 +/- 29.2, 131.9 +/- 5 0.1, and 151.3 +/- 54.0 pixels(2)/s respectively). Retinal blood flow was also significantly (P < 0.05) reduced in the 4-week untreated diab etic rats compared with nondiabetic rats (95.7 +/- 22.2 vs. 125.7 +/- 29.5 pixels(2)/s). In contrast to the shorter-duration group, insulin treatment for 1 week after 3 weeks of diabetes did not totally normali ze retinal blood flow (117.5 +/- 32.4 pixels(2)/s). These results sugg est that vascular abnormalities could become more resistant to normali zation following short-term (1 week) insulin treatment after longer pe riods of untreated diabetes.