Experimental studies on the mechanism of action of timolol.

Timolol, which binds to beta-adrenergic receptors, is a potent antagonist of the catecholamine-stimulated synthesis of cyclic AMP. However, the actual mechanism of action by which timolol reduces intraocular pressure is not readily apparent. Compared to its efficacy in human eyes, the drug is relatively ineffective in rabbit eyes. A reasonable postulate is that soon after administration, timolol blocks endogenous adrenergic stimulation contributing to the formation of aqueous humor by the ciliary processes. Nevertheless, the long-lasting reduction of intraocular pressure persists at a time when the drug is no longer bound to beta-adrenergic receptors.