The Effect of Timolol on the Iris Vascular Tone in Rats

Abstract

We investigated, in rats, the existence of a cathecolaminergic vasodilator tone in iris vessels, using as a pharmacological tool, timolol, a non-selective β-blocker, devoided of intrinsic sympathomimetic activity. The use of 2.5 mM timolol in conjunctival instillation reduced the diameter of the iris arteries without having an effect on the size of the iris veins diameter. Our results suggest the existence of a catecholaminergic vasodilator tone in rat's iris arteries, not in iris veins, probably achieved via β2-adrenergic receptors.