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E. ALBERT ZELLER, DAVID SHOCK, STEVEN G. COOPERMAN, ROBERT I. SCHNIPPER; Enzymology of the refractory media of the eye IX. On the role of monoamine oxidase in the regulation of aqueous humor dynamics of the rabbit eye. Invest. Ophthalmol. Vis. Sci. 1967;6(6):618-623.
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To find out whether monoamine oxidase (MAO) plays any role in the dynamics of the aqueous humor, we tried to block this enzyme in the anterior part of the rabbit eye. Since trans-2-phenylcyclopropylamine, which combines the properties of a sympathomimetic amine and MAO inhibitor, appears in the anterior chamber within a few minutes after conjunctival instillation as indicated by mydriasis, it was considered probable that another aralkyl-amine, N-benzyl-N-methypropynylamine (pargyline), one of the most potent MAO inhibitors, would reach intraocular MAO. Actual determinations with a sensitive photometric method of MAO activity in the homogenate made of iris and ciliary body confirmed this assumption. Albino rabbits, after extensive tonographic determination of their aqueous humor dynamics, received repeated instillations of the pargyline solution into the right eye. As early as 4 hours after the first instillation, we observed, highly significant depression of the intraocular pressure, apparently caused by a significant reduction of the rate of aqueous formation, since no alteration in the outflow facility occurred. For two weeks of treatment the tonographic data remained essentially the same. In contrast to the phenylctjclopropylamine experiments, no change in the pupillary size took place after pargyline instillations. In the left eyes of treated rabbits and in eyes of various control animals, these changes were entirely absent. The observational data remained essentially the same for the two weeks of treatment. The mechanism of this reaction remains to be elucidated. Transfer of catecholamines or serotonin into the aqueous sufficient to produce pupillary dilatation had to be excluded as a critical event
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