Evaluation of retinal microcirculatory alterations in the Goto-Kakizaki rat. A spontaneous model of non-insulin-dependent diabetes.

Purpose: To evaluate retinal microcirculation in the spontaneous diabetic GK (Goto-Kakizaki) rat over an extended time.
Methods: The dye-dilution technique with scanning laser ophthalmoscope-based fluorescein angiography was used to evaluate retinal circulation in GK rats with diabetes of 1, 3, and 5 months' duration and in age-matched controls. Scanning laser ophthalmoscope fluorescein angiograms were recorded after a 10-microliter bolus of 10% sodium fluorescein was injected into the tail vein, followed by a flush of 0.1 ml saline. Retinal mean circulation times (MCTs), vessel diameters, and retinal segmental blood flows (SBFs) were determined using computer-assisted image analysis on a frame-by-frame basis.
Results: The MCTs were significantly prolonged (P< 0.01) in the GK rat groups (2.60 +/- 0.31, 2.74 +/- 0.28, and 2.84 +/- 0.38 seconds at 1, 3, and 5 months' duration of diabetes, respectively) compared to the age-matched controls (1.94 +/- 0.20, 1.99 +/- 0.12, and 1.91 +/- 0.22 seconds, respectively). No significant differences were observed in the retinal arterial and venous diameters between groups at each time period. The SBFs were significantly reduced (P< 0.03) in the GK rat groups (12.0 +/- 1.5, 12.1 +/- 2.0, and 11.8 +/- 2.5 x 10(2) micrometer squared/second at 1, 3, and 5 months' duration of diabetes, respectively) compared to the controls (16.0 +/- 2.2, 16.7 +/- 1.8, and 17.2 +/- 2.5 x 10(2) micrometer squared/second, respectively). In either group, no significant changes with growth were observed in MCT, vessel diameters, or SBF, although the MCTs in the GK rat group tended to lengthen, and arterial and venous diameters in the GK rat group tended to increase with duration of diabetes. Goto-Kakizaki rats did not exhibit dense cataracts, the retinal circulation could be observed, and morphologic changes of diabetic retinopathy did not develop throughout the experimental period.
Conclusions: A significant prolongation in MCT and a significant reduction in SBF appeared in GK rats at an early stage in diabetes. This tendency continued until 5 months' duration of diabetes. These results suggest that retinal circulatory abnormalities are found before observable retinopathy development in GK rats and that there may be some mechanism causing a reduction in SBF without changing major retinal vessel diameters at an early stage in non-insulin-dependent diabetes mellitus (NIDDM). In addition, this study demonstrates that the GK rat will be a useful model of non-insulin-dependent diabetes mellitus to evaluate retinal circulation over an extended time.