Timolol Adrenaline

The peripheral receptors activated by noradrenaline fall into at least two classes, a-receptors and /3-receptors, which differ in their function and in their response to drugs. The a-receptors cause constriction of blood vessels and compounds used to block them include indoramin (216), prazosin (217) and phentolamine (218). Another imidazoline, tolazoline (2-benzyl-2-imidazoline), is a useful vasodilator but is unsuitable for the treatment of hypertension since it stimulates the heart. Other drugs described as peripheral vasodilators are diazoxide (219), which is related to the thiazide diuretics, hydralazine (220) which also depresses the CNS, hydracarbazine (221) and minoxidil (222). The /3-receptors control the action of adrenaline on the heart (among other effects) and the agents that block them are mostly nonheterocyclic aromatic compounds with aminoethanol or 3-amino-2-hydroxypropoxy side-chains. They have proved effective in the treatment of hypertension. One heterocyclic compound of this class, timolol (223), is in use. 

Timolol is a ffb locker that blocks one action of adrenaline (epinephrine) and keeps heart disease at bay by counteracting high blood pressure. 

Cystoid macular edema has been reported to occur in 2.8% of the patients receiving adrenaline especially in aphakic or pseudophakic eyes (13). Cystoid macular edema has also been seen after the use of dipivefrine, but in the classic case described in 1982 pretreatment with timolol maleate may have predisposed the eye to this complication (14). 

Beta-blockers, by inhibiting the effect of adrenaline and noradrenaline on the heart, prevent the normal increase in heart rate, and are very effective in preventing exercise angina. Examples of beta-blockers used for this purpose include acebutolol, atenolol, metoprolol. nadolol, oxprenolol, pindolol, propranolol, sotalol and timolol. See ADRENOCEPTOR ANTAGONISTS. 

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