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Probenecid inhibition of the outward transport of fluorescein across the human blood‐retina barrier

1994; Wiley; Volume: 72; Issue: 6 Linguagem: Inglês

10.1111/j.1755-3768.1994.tb04676.x

1755-3768

C. Engler, Birgit Sander, Michael Larsen, Pernille Koefoed, Hans‐Henrik Parving, Henrik Lund‐Andersen,

Retinal Development and Disorders

Abstract. The effect of probenecid on the outward transport of fluorescein from vitreous to blood was studied in 13 insulin‐dependent diabetic patients with background retinopathy in a randomised double‐masked placebo controlled cross‐over study. Fluorescein and fluorescein glucuronide were separated in the vitreous and in plasma by differential spectrofluorometry. The data for fluorescein were analysed using a simplified mathematical model of the eye. The inward permeability was estimated from data obtained 1 h after injection and the outward transport from data obtained 7 h after injection. During placebo treatment the mean inward permeability was 3.75 times 10 −7 cm/sec and the mean outward permeability was 2.25 times 10 −5 cm/sec. During probenecid treatment the mean inward permeability was 3.34 times 10 −7 cm/sec and the mean outward permeability was 1.44 times 10 −5 cm/sec. Thus, we found no significant change in inward permeability (p = 0.5879), whereas a significant decrease of 36% was found in the outward permeability of fluorescein (p = 0.0171). The demonstration that the outward permeability, which is more than 100‐fold higher than the inward permeability in the healthy eye, is significantly decreased by probenecid, demonstrates that active transport is involved in movement of fluorescein across the blood‐retina barrier from the vitreous to the plasma.