title: Resistance to blood flow in the rabbit ophthalmic artery after topical treatment with timolol.
abstract: OBJECTIVE
  The aim of this study was to investigate the resistance to blood flow in the ophthalmic artery of rabbits receiving topical treatment with timolol.
  
  
  METHODS
  Eight (8) New Zealand albino rabbits received 20 mul of timolol treatment (vehicle, 0.1%, 0.33%, 1%, and 3.3%) on the right eye. Blood-flow velocity in the ophthalmic artery was determined in the treated eye using color Doppler imaging (CDI) with a 12-MHz linear ultrasound transducer prior to the treatment and at 0.5, 1, 1.5, 2, and 3 h after the treatment. Intraocular pressure (IOP) was measured in both eyes, using a pneumatonometer at the same time points. Pourcelot's resistive index of blood flow was calculated, using the peak systolic velocity and the end diastolic velocity. A control experiment was performed with CDI obtained from the right eye when the left eye was treated with 1% timolol.
  
  
  RESULTS
  In the eye treated with 1% and 3.3% timolol, a dose-dependent increase in the resistive index of blood flow occurred in the ophthalmic artery. No change in the resistive index occurred when the contralateral eye was treated with 1% timolol. Changes of IOP were not different between the two eyes under all the experimental conditions. Timolol, at all concentrations, caused a significant reduction of heart rate. A similar reduction of heart rate occurred when either eye was treated with 1% timolol.
  
  
  CONCLUSIONS
  Topical treatment with timolol in rabbits can increase the resistance to blood flow in the ophthalmic artery. This effect is caused by a mechanism local to the eye and is not dependent on an IOP change.
authors: Hamilton Glaucoma Center and Department of Ophthalmology, University of California-San Diego, La Jolla, CA 92039-0946, USA. joliu@ucsd.edu
authors: John H K
authors: JH
authors: Liu
authors: Ruixia
authors: R
authors: Li
authors: Thomas R
authors: TR
authors: Nelson
authors: Robert N
authors: RN
authors: Weinreb
mesh_terms: D000287:Administration, Topical; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005123:Eye / Q000098:blood supply; D006339:Heart Rate / Q000187:drug effects; D007429:Intraocular Pressure / Q000187:drug effects*; D009880:Ophthalmic Artery / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects; D013999:Timolol / Q000494:pharmacology*; D018615:Ultrasonography, Doppler, Color
chemical_list: D000319:Adrenergic beta-Antagonists; D013999:Timolol