Effect of brimonidine on optic nerve blood flow in rabbits.
OBJECTIVE
Brimonidine is a highly selective alpha2-adrenoreceptor agonist that lowers intraocular pressure. The aim of the present study was to analyze in vivo the vasomotor effects and the influence of brimonidine on blood flow within the optic nerve, by means of intraluminal microvascular corrosion casting technique and intravascular injection of colored microspheres.


METHODS
New Zealand white rabbits received either brimonidine tartrate 0.2% or placebo (vehicle) topical drops in one eye for 4 weeks. Intraocular pressures were measured at baseline and 4 weeks. The anterior optic nerve microvasculature of four rabbits was examined with corrosion castings for regions of focal vasoconstriction. Optic nerve blood flow was determined in 16 rabbits by means of nonradioactive colored microspheres.


RESULTS
The vasoconstriction values of the short posterior ciliary arterial branches in the brimonidine eyes were 16.7%+/-3.7%. In the fellow untreated eyes, the mean vasoconstriction was 16.6%+/-2.4%. In the placebo-treated eyes, the average constriction was 15.9%+/-3.2%; the fellow eyes showed a mean constriction value of 16.1%+/-5.3%. There was no statistical difference between any of the groups (P = .2). The optic nerve blood flow in the brimonidine-treated rabbits was 0.18+/-0.06 ml/mg/min and 0.17+/-0.04 ml/mg/min in the treated and the fellow eyes, respectively. The difference between the optic nerve blood flow in the brimonidine-treated eyes and the optic nerve blood flow in all of the untreated eyes (0.19+/-0.06 ml/mg/min) also was not statistically different (P = .82).


CONCLUSIONS
Long-term application of brimonidine 0.2% does not affect the blood flow or vasomotor activity of the anterior optic nerve.
Bhandari
A
A
Discoveries in Sight, Devers Eye Institute, Legacy Health System, Portland, Oregon 97210, USA.
Cioffi
G A
GA
Van Buskirk
E M
EM
Orgül
S
S
Wang
L
L
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D000068438:Brimonidine Tartrate; D002924:Ciliary Body / Q000098:blood supply; D016319:Corrosion Casting; D005260:Female; D008297:Male; D008833:Microcirculation / Q000187:drug effects; D008863:Microspheres; D009900:Optic Nerve / Q000098:blood supply*; D011810:Quinoxalines / Q000494:pharmacology*; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects; D014661:Vasoconstriction; D014666:Vasomotor System / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D000068438:Brimonidine Tartrate