Vitreous fluorescein accumulation determined by in vivo fluorophotometry and by vitreous extraction in normal and diabetic rats

Abstract

Summary.Vitreous fluorophotometry was performed on pigmented male rats (Piebald strain) 2 weeks after induction of diabetes by streptozotocin. In vivo fluorophotometry data were compared with measurements obtained by direct extraction of the vitreous 60 rain after an intravenous injection of sodium fluorescein. In addition, the rate of fluorescein disappearance from blood plasma, plasma protein binding of fluorescein and the effect of insulin treatment of diabetic animals were investigated. Age-matched nondiabetic animals served as controls. In vivo fluorophotometric measurements showed a good correlation with fluorescein determinations after direct extraction of the vitreous. Vitreous fluorescein concentrations were similar in diabetic and normal rats and were strongly related to the dye plasma levels within each group of animals. In the diabetic rats, however, the elimination of plasma fluorescein was accelerated and the percentage of free fluorescein, as determined by ultrafiltration and equilibrium dialysis, was consistently higher (130-150% of controls). The ratios of vitreous to total or free plasma fluorescein levels were elevated in diabetic rats. Experimental data indicate that plasma concentration of free fluorescein is crucial for vitreous dye accumulation. Insulin treatment of diabetic rats markedly improved their metabolic state and normalized the plasma fluorescein elimination and the vitreous to plasma fluorescein concentration ratios. It is concluded that vitreous fluorophotometry can be adequately applied to pigmented rats, provided that plasma fluorescein elimination rate and protein binding are considered in the interpretation of the results, since both influence the vitreous fluorescein accumulation and both may be altered by disease and drug treatment.Key words: Rat, streptozotocin diabetes, vitreous fluorophotometry, vitreous fluorescein extraction, insulin, fluorescein pharmacokinetics, fluorescein protein binding.Vitreous fluorophotometry, an in vivo method of assessing fluorescein levels in the vitreous body after a systemic application, was introduced some years ago in medical research. Ever since, several authors [1-3] have reported enhanced vitreous fluorescein concentrations in diabetic patients without angiographically detectable retinopathy. It was then suggested that elevated vitreous fluorescein levels may represent the earliest abnormality in developing diabetic retinopathy and indicate a breakdown of the blood retinal barrier. Tight metabolic control resulted in a normalization of the vitreous fluorophotometric readings [4]. Other groups have been unable to demonstrate any alteration between healthy and diabetic patients without observable retinopathy [5,6]. The technique was also applied to study the effect of experimentally induced diabetes by streptozotocin or pancreatectomy on the blood retinal barrier in rats. As in studies on man, these studies yielded conflicting results. Elevated vitreous fluorescein levels [7,8] in diabetic rats which could be normalized by insulin tre...

Changes in vitreal oxygen tension distribution in the streptozotocin diabetic rat

“…A large amount of histological data has subsequently been accumulated from human tissue and animal models of induced diabetes which support these original conclusions [4][5][6][7][8][9]. In parallel with these structural alterations there is evidence for concomitant functional changes with an early reduction in the integrity of the blood retinal barrier which probably occurs initially at the level of the retinal pigment epithelial cells [10][11][12][13][14][15][16]. Added to this is the data demonstrating that erythrocyte properties are affected directly in response to the induced hyperglycaemia, so that blood volume expands, and glycosylation of haemoglobin and other bloodproteins leads to an increase in erythrocyte fragility and a decrease in deformability [17][18][19][20][21].…”

Titanium dioxide nanoparticles impair the inner blood-retinal barrier and retinal electrophysiology through rapid ADAM17 activation and claudin-5 degradation

“…The eyeballs were then isolated and homogenized on the next day, followed by fluorescein intensity quantification. Generally speaking, the injected sodium fluorescein was completely eliminated after 24 h, whereas the leaking fluorescein remaining in the vitreous body was excluded slowly [25]. Quantitative data showed a dose-dependent accumulation of fluorescein in TiO 2 -(See figure on previous page.)…”