Carboxyfluorescein distribution in ocular tissues of normal and diabetic rats

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Abstract
Quantitative fluorescence microscopy was used to study carboxyfluorescein distribution across the blood-ocular barriers of control and streptozotocin diabetic rats at 2 min, 1 and 2 hr after dye injection (125 mg/kg iv). Measurement of dye concentrations in plasma, urine and feces demonstrated increased plasma clearance and increased urinary clearance of carboxyfluorescein in diabetic rats. Unbound plasma dye concentration in the diabetic animals fell to 34% of the control level at 1 hr after injection; the corresponding plasma concentration vs. time integral was reduced to only 74% of the control value. The presence of a less fluorescent glucuronide conjugate of carboxyfluorescein was not detected in plasma, urine or feces. Fluorescence intensity in the ocular tissues measured, including choriocapillaris, pigment epithelium, retina, ciliary epithelium, iris, and cornea, was not higher for diabetic than for control rats. In addition, there was no indication of localized dye leakage into retina through defects in the pigment epithelial and vascular endothelial barriers or of increased dye entry at the optic disc, a site of blood-retinal barrier discontinuity. Normalization of tissue fluorescence intensity measurements at the different time intervals to compensate for disparity in concurrent plasma dye concentrations resulted in significantly higher levels in diabetic retinas at 1 hr. However, because this difference was not manifest when the plasma dye concentration vs. time integral was used to normalize the data, it is concluded that no greater accumulation of carboxyfluorescein occurs in the retina of diabetic rats over the time period studied.