Influence of topical and systemic beta-blockers on tear production

The influence of various beta-blockers on tear production in rabbits was studied by means of direct cannulation of the lacrimal gland excretory duct. Tear production was significantly decreased (p less than 0,001) after systemic (I.M.) administration of either selective beta 1-blockers (metoprolol, betaxolol), B2-selective (butoxamine) or non-selective ones (timolol, propranolol) or finally those with I.S.A. (oxprenolol), although differences in the size of tear production decreasing response of each beta-blocker were recorded. Bilateral topical application of timolol (50 microliters of 0,5% b.i.d. for three days), decreased also tear production significantly, while the response of betaxolol administered under the same regime was rather negligible. It is concluded that although beta 2 adrenergic receptors are mainly involved in tear production, the administration of selective beta 1-blockers in high doses disappears their selectivity, decreasing tear production too.