Effects of selective inhibition of type A and type B monoamine oxidase on intraocular pressure in the cat and the rabbit.

Ocular tension of conscious cats and rabbits was measured after topical application of clorgyline, a selective inhibitor of type A monoamine oxidase, or deprenyl, a selective inhibitor of line (1,4 and 12%) showed a dose-related reduction of intraocular pressure, with maximal lowerings amounting to 6 to 7 mm Hg. Pretreatment of eyes with clorgyline, 1%, markedly potentiated the pressure lowering response to epinephrine, 0.1%, applied topically. Sympathetic denervation almost completely abolished the effect of clorgyline. In contrast, deprenyl (2 to 8%) did not lower intraocular pressure after topical application to cat or rabbit eyes. beta-Phenylethylamine (2 to 16%) a specific substrate for the B form of monoamine oxidase, likewise did not lower ocular tension when given either alone or after pretreatment with deprenyl. These findings suggest that the intraocular pressure lowering effect of monoamine oxidase inhibitors is due primarily to inhibition of the A form of the enzyme and is dependent on intact sympathetic innervation.