Timolol

Timolol competes with adrenergic neurotransmitters for binding to beta(1)-adrenergic receptors in the heart and the beta(2)-receptors in the vascular and bronchial smooth muscle. This leads to diminished actions of catecholamines, which normally bind to adrenergic receptors and exert sympathetic effects leading to an increase in blood pressure and heart rate. Beta(1)-receptor blockade by timolol leads to a decrease in both heart rate and cardiac output during rest and exercise, and a decrease in both systolic and diastolic blood pressure. In addition to this, a reduction in reflex orthostatic hypotension may also occur. The blockade of beta(2) receptors by timolol in the blood vessels leads to a decrease in peripheral vascular resistance, reducing blood pressure.

The exact mechanism by which timolol reduces ocular pressure is unknown at this time, however, it likely decreases the secretion of aqueous humor in the eye. According to one study, the reduction of aqueous humor secretion may occur through the decreased blood supply to the ciliary body resulting from interference with the active transport system or interference with prostaglandin biosynthesis.