Comparative study on the combined effects of bunazosin and nipradilol or timolol on intraocular pressure in normotensive rabbits

Purpose: To compare the ocular hypotensive effect of nipradilol and timolol in combination with bunazosin in rabbits. Methods: The intraocular pressure (IOP) in normal rabbits was measured using an applanation pneumatonograph. Nipradilol, timolol, and bunazosin were instilled, individually or in combination, into the inferior conjunctival sac. Results: Nipradilol (0.25%), timolol (0.5%), and bunazosin (0.01%) individually lowered IOP. The IOP-lowering effects of both nipradilol and timolol were significantly enhanced by the combined application of bunazosin (0.01%). In the presence of 5% timolol or 0.1% bunazosin, IOP was further lowered by the addition of nipradilol. The IOP-lowering effect of nipradilol was partly inhibited by pretreatment with c-PTIO (10 mM), a nitric oxide (NO)-trapping agent. Conclusions: The present study demonstrated that the IOP-lowering effects of nipradilol are due to β- and α1-blocking and NO-donating actions, and bunazosin has an additive effect on the IOP-lowering effect of nipradilol or timolol.