[Mechanism of action of beta-blockers]

If beta-blockage does not cause lowering of aqueous humor secretion, in itself responsible for the maintenance of intraocular pressure, what is the mechanism of action? The antagonism for indolamines, recently measured in aqueous humor, the absence of nocturnal effect, and the amplitude diminution of diurnal variations thus produced suggest that beta-blockers could interact with indolamines, since the latter are probably responsible for intraocular pressure regulation. Aqueous humor secretion depends to a major extent on the sodium-potassium pump and its enzyme, Na+K(+)-ATPase. Serotonin, known for its activating action on Na+K(+)-ATPase, is present in the greatest amounts in the morning, precisely when the aqueous humor secretion is the highest. Moreover, timolol is a potent antagonist of serotonin, suggesting that beta-blockers could decrease the secretion by antagonism with serotonin at the level of Na+K(+)-ATPase. Since serotonin is metabolized to melatonin during sleep, beta-blockers might simulate a state of sleep of the ciliary epithelium.