APRACLONIDINE PROTECTION OF THE BLOOD-AQUEOUS BARRIER FROM TRAUMATIC BREAKDOWN

This study investigated the effects of apraclonidine hydrochloride 1% eye drops on blood-aqueous barrier in 108 pigmented rabbits. The effec ts of pretreatment with dapiprazole and yohimbine, and a comparison wi th clonidine 0.125% eye drops are also reported. The disruption of blo od-aqueous barrier was obtained by argon laser burning of the iris. Th e degree of permeability of the barrier was deduced by the amount of p roteins in aqueous humor 60 min after laser application. Intraocular p ressure and pupil diameter were also studied. Protein content in aqueo us humor was 0.72 +/- 0.26 g/l in control rabbits that did not receive any treatment; 5.98 +/- 4.23 g/l in rabbits instilled with placebo ey e drops and treated by laser burning of iris; 0.43 +/- 0.25 g/l in rab bits that received apraclonidine eye drops prior to laser burning; 2.1 9 +/- 1.3 g/l in rabbits that received apraclonidine eye drops immedia tely after laser application; 0.35 +/- 0.08 g/l in rabbits that receiv ed apraclonidine 1% eye drops both before and after laser application. Rabbits treated with clonidine 0.125% had a protein content in aqueou s humor of 5.45 +/- 2.08 g/l after laser application. Dapiprazole 0.5% eye drops prior to apraclonidine led to a protein content in aqueous humor of 1.93 +/- 2.13 g/l; yohimbine 0.3% eye drops prior to apraclon idine led to a protein content of 0.70 +/- 0.40 g/l. Protein content i n aqueous humor was 0.93 +/- 0.36 g/l, 0.82 +/- 0.899 g/l and 1.68 +/- 1.39 g/l in rabbits treated with yohimbine 0.3,0.6 and 1.2 mg/kg i.v. and then with apraclonidine 1% eye drops. In one group of rabbits, th e penetration into the aqueous humor of Evans blue injected intravenou sly was also studied. Evans blue content in aqueous humor was 0.03 +/- 0.08 mg/100 ml in control rabbits; 0.92 +/- 0.53 mg/100 ml in placebo rabbits treated by laser; and 0.28 +/- 0.19 mg/100 ml in apraclonidin e rabbits treated by laser. Apraclonidine eye drops led to a decrease in IOP and prevented IOP rise following argon laser application. Place bo treated rabbits had a 20% increase in IOP following laser applicati on. Apraclonidine-treated eyes showed mydriasis and blanching of the c onjunctiva. These effects were not affected by pretreatment with dapip razole or yohimbine. In these experiments, the treatment with apraclon idine 1% eye drops completely protected the blood aqueous barrier from the disruption caused by laser burning of the iris. The protection wa s less effective when apraclonidine was applied after laser burnings.