Effects of Timolol and Betaxolol on Choroidal Blood Flow in the Rabbit

• Published in: Experimental eye research Vol. 67; no. 5; pp. 501 - 507
• Main Authors: KIEL, J.W., PATEL, P.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01-11-1998; Elsevier
• Subjects: Adrenergic beta-Antagonists - pharmacology; Animals; arterial pressure; Betaxolol - pharmacology; Biological and medical sciences; Blood Pressure - drug effects; choroid; Choroid - blood supply; Eye; Female; In Vitro Techniques; intraocular pressure; Intraocular Pressure - drug effects; Laser-Doppler Flowmetry; Medical sciences; Pharmacology. Drug treatments; Rabbits; Regional Blood Flow - drug effects; Timolol - pharmacology; Vascular Resistance - drug effects; choroid; eye; arterial pressure; intraocular pressure; Antiglaucomatous agent; Betaxolol; Rabbit; Choroid; Lagomorpha; Blood flow; β-Adrenergic receptor; Eye; Vertebrata; Mammalia; Animal; Hemodynamics; Antagonist; Timolol; Beta blocking agent; Intraocular pressure
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1006/exer.1998.0553

This study evaluated the effects of the topical β1-adrenergic antagonist betaxolol and the non-selective β-adrenergic antagonist timolol on the choroidal pressure–flow relationship. Pentobarbital-anesthetized rabbits were instrumented with hydraulic occluders on the aorta and inferior vena cava to control MAP, an ear artery cannula to measure mean arterial pressure (MAP), and two vitreous cannulas to control and measure intraocular pressure (IOP). Choroidal blood flow was measured by laser Doppler flowmetry with the fiber-optic probe tip positioned over the posterior pole. Choroidal pressure–flow curves were obtained before and 30 min after topical application of 0.1 ml of betaxolol (Betoptic, 0.5%,n=10), timolol (Timoptic, 0.5%,n=10) or saline (n=8) by varying the MAP without controlling the IOP and by raising IOP while holding the MAP constant at 70 mmHg. The IOP was significantly reduced by betaxolol and timolol but not by saline. MAP was also slightly, but significantly, reduced after betaxolol but not after timolol or saline. However, the systemic hypotensive response to isoproterenol (8 μg/kg, i.v.) was blunted after betaxolol and timolol indicating appreciable systemic absorption of both drugs. Timolol, but not betaxolol or saline, caused a significant, small increase in baseline choroidal vascular resistance. Timolol also attenuated the IOP response to MAP; however, none of the treatments had a significant effect on the choroidal pressure–flow relationship. We conclude that both drugs reach the systemic circulation after topical application, but neither betaxolol nor timolol alter the choroidal response to acute changes in perfusion pressure.