Retinal uptake index method

The RUI method is a modification of the brain uptake index method [29] which was first described by Aim and Tornquist [4], The RUI approach consists of a single-arterial (e.g., intracarotid) injection technique, where the primary objective is to analyze the influx of the test substrate from the circulating blood to the retina through the BRB (i.e., blood-to-retina direction). This approach, for example, has been used to determine the retinal uptake of the test substrate which has a relatively high permeability across the BRB. The advantage of this approach is that it avoids the effect of plasma-protein binding of the test substrate and allows the retinal uptake of the test substrate 

In brief, the rats are anesthetized, followed by an injection of 0.2 mL of the test solution into the common carotid artery. The injection solution consists of a HEPES buffered Ringer s solution (containing 141 mM NaCl, 4 mM KC1, 2.8 mM CaCl2, and 10 mM HEPES, pH 7.4) which contains both the test substrate (e.g., a [3H]-labeled compound, about 10 /xCi) and a reference compound, which is highly extracted by the tissue (e.g., 0.1 /xCi [14C]n-butanol) in the presence or absence of transport inhibitors. If a [14C]-labeled compound is used as a test substrate, [3H]H20 can be selected as a reference compound. Rats are decapitated at 15 s after injection and the retina is removed. The retina is dissolved in 2 N NaOH and subsequently neutralized with 2 N HC1. The radioactivity is measured by liquid scintillation spectrometry. The RUI value, an index of the retinal distribution characteristics of the [3H] test substrate, is estimated using the following relationship  

In Vivo Vitreous/Retina-to-Blood Efflux Transport (Microdialysis Study) 

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A. Aim and P. Tornquist. The uptake index method applied to studies on the blood-retinal barrier. I. A methodological study. Acta Physiol. Scand. 113 73-79 (1981). 

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