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Birgitte Moldow, Birgit Sander, Michael Larsen, Henrik Lund–Andersen; Effects of Acetazolamide on Passive and Active Transport of Fluorescein across the Normal BRB. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1770-1775.
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purpose. To investigate the effect of the carbonic anhydrase inhibitor
acetazolamide (AZM) on passive permeability and active transport of
fluorescein across the blood-retina barrier in healthy subjects. The
study may have implications for the understanding of the edema-reducing
effect of AZM.
methods. The effect of AZM on the blood-retina barrier function was assessed by
differential vitreous spectrofluorometry using fluorescein as a tracer.
The study included fourteen healthy subjects in a randomized
double-masked crossover trial with 3 days’ treatment with AZM (500
mg/d) and placebo, respectively. The two examinations were separated by
at least 1 week. Fluorescein concentration was determined separately
from its metabolite fluorescein glucuronide. The passive permeability
of fluorescein was determined by computerized modeling and
curve-fitting to the preretinal curve and the plasma concentration
curve obtained at 30 to 60 minutes after the injection of fluorescein.
The unidirectional permeability due to outward active transport from
vitreous to blood was estimated from the preretinal gradient and the
plasma concentration at 7 to 10 hours after injection.
results. Treatment with AZM was associated with significant increases in passive
permeability and unidirectional permeability of fluorescein. For the
passive permeability the increase was on average 0.3 ± 0.4 nm/s
(mean ± SD; range, −0.8–1.0 nm/s), and for the unidirectional
permeability the increase was on average 7.4 nm/s ± 7.0
(mean ± SD; range, −3.3–19.0 nm/s).
conclusions. Acetazolamide caused an increase in passive permeability.
Unidirectional permeability was increased by AZM, indicating a
stimulation of the outward active transport of fluorescein. It has been
proposed that the edema-reducing effect of AZM is due to stimulated ion
and fluid removal from the retina to the choroid. The results of this
study are consistent with AZM affecting the blood-retina barrier with
stimulation of at least one ion transport mechanism.
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