Potent Reduction of Intraocular Pressure by Nipradilol Plus Latanoprost in Ocular Hypertensive Rabbits

Abstract

The present study was performed to evaluate the intraocular pressure (IOP)-lowering effect of nipradilol in combination with latanoprost on ocular normotensive and hypertensive rabbits. IOP was measured using an applanation pneumatonograph under topical application of 0.4% oxybuprocaine hydrochloride for corneal anesthesia. Ocular hypertension was induced by injection of 0.1 ml hypertonic saline (5% NaCl) into the vitreous body. Saline, nipradilol, latanoprost, sodium nitroprusside (SNP) or indomethacin was then instilled just after 5% NaCl injection. All drugs were instilled in the inferior conjunctival sac, using 50 microl drops. If more than two drugs were used, they were applied 5 min apart. Nipradilol lowered IOP in both ocular normotensive rabbits and ocular hypertensive rabbits, whereas latanoprost did not lower IOP in either. When nipradilol was applied in combination with latanoprost, the reduction in ocular hypertension was significantly enhanced, compared to the effect of nipradilol alone. A significantly potent reduction in ocular hypertension was also observed by the SNP-latanoprost combination. The IOP-lowering effects of SNP in combination with latanoprost were abolished by treatment with indomethacin. These results indicate that the IOP-lowering effect of latanoprost was enhanced when applied in combination with nipradilol or SNP, both of which have nitric oxide (NO)-donating actions. Since both combined effects were abolished by treatment with indomethacin, the mechanisms by which nipradilol combined with latanoprost lowered ocular hypertension may be related, at least in part, to the production of prostaglandins via the NO-donating action of nipradilol.