Effects of bunazosin hydrochloride on ciliary muscle constriction and matrix metalloproteinase activities.

PURPOSE: To clarify the mechanism by which bunazosin hydrochloride (BZ), a selective alpha1-adrenoceptor antagonist, increases uveoscleral outflow.

METHODS: The effects of BZ on matrix metalloproteinase (MMP) activities in cultured monkey ciliary muscle cells, and on phenylephrine hydrochloride-induced constriction in bovine ciliary muscles, were examined. Also, the possible additive ocular hypotensive effects of BZ and latanoprost (LP) were evaluated in ocular normotensive monkeys.

RESULTS: Although BZ at 10 to 10 M did not increase MMP-2, -3, and -9 activities in the culture medium of ciliary muscle cells, BZ at 10 to 10 M inhibited phenylephrine hydrochloride-induced constriction in ciliary muscles. The maximal reduction in intraocular pressure of concomitant administration of BZ and LP was greater than that of BZ alone and tended to be greater than that of LP alone.

CONCLUSION: These findings, in normotensive monkeys, indicate that the mechanism whereby BZ increases uveoscleral outflow is independent of an effect on MMPs and is partly due to relaxation of the ciliary muscle. This effect is different from that of LP, which might help to explain the finding that topical concomitant administration of BZ and LP increased AUC(0-6h) value (IOP reduction) to 201% and 145% of BZ and LP given alone, respectively.