title: Probenecid inhibition of the outward transport of fluorescein across the human blood-retina barrier.
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 was 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 x 10(-7) cm/sec and the mean outward permeability was 2.25 x 10(-5) cm/sec. During probenecid treatment the mean inward permeability was 3.34 x 10(-7) cm/sec and the mean outward permeability was 1.44 x 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.
authors.affiliation: Department of Ophthalmology, Gentofte Hospital, University of Copenhagen, Denmark.
authors.forename: C B
authors.initials: CB
authors.lastname: Engler
authors.forename: B
authors.initials: B
authors.lastname: Sander
authors.forename: M
authors.initials: M
authors.lastname: Larsen
authors.forename: P
authors.initials: P
authors.lastname: Koefoed
authors.forename: H H
authors.initials: HH
authors.lastname: Parving
authors.forename: H
authors.initials: H
authors.lastname: Lund-Andersen
mesh_terms: D000328:Adult; D001693:Biological Transport, Active / Q000187:drug effects; D001769:Blood / Q000378:metabolism; D001813:Blood-Retinal Barrier / Q000187:drug effects*; D002199:Capillary Permeability / Q000187:drug effects; D018592:Cross-Over Studies; D003922:Diabetes Mellitus, Type 1 / Q000150:complications / Q000378:metabolism; D003930:Diabetic Retinopathy / Q000150:complications / Q000378:metabolism; D004311:Double-Blind Method; D019793:Fluorescein; D005452:Fluoresceins / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011339:Probenecid / Q000494:pharmacology*; D014822:Vitreous Body / Q000378:metabolism
chemical_list: D005452:Fluoresceins; D011339:Probenecid; D019793:Fluorescein