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Abstract #16907 Published in IGR 9-1
Effect and mechanism of βxolol and timolol on vascular relaxation in isolated rabbit ciliary artery
Dong Y; Ishikawa H; Wu Y; Shimizu K; Goseki T; Yoshitomi TJapanese Journal of Ophthalmology 2006; 50: 504-508
PURPOSE: In order to clarify the vasodilatory mechanism of betaxolol and timolol, we studied the effects of these drugs in isolated rabbit ciliary arteries. METHODS: Rabbit ciliary artery specimens were mounted in a double myograph system, and betaxolol, timolol, or another agent was introduced into the organ chamber. The mechanical response of the arteries was studied using an isometric tension recording method. The intracellular free calcium concentration [Ca2+ ]i was also measured using fluorescence photometry. RESULTS: Betaxolol and timolol induced dose-dependent relaxation in the rabbit ciliary arteries precontracted by high-K+ Krebs solution. The minimum concentrations required to cause relaxation were 10 μM of betaxolol, and 30 μM of timolol. At the maximum concentration of 1 mM, betaxolol induced almost complete relaxation of the ciliary arteries, whereas timolol induced approximately 70% relaxation. These actions were not inhibited by pretreatment with 100 μM NG-nitro-l-arginine methylester (L-NAME), a nitric oxide synthase inhibitor, or by denudation of the vascular endothelium. However, 300 μM of betaxolol or timolol decreased the [Ca2+ ]i of the vascular smooth muscle, an action similar to that of diltiazem, a typical L-type voltage calcium-channel blocker. CONCLUSIONS: Betaxolol, a selective β1-adrenoceptor antagonist, and timolol, a nonselective β-adrenoceptor antagonist, both frequently used in the medical management of glaucoma, decrease [Ca2+ ]i by acting as Ca2+ channel blockers, thus causing relaxation of isolated rabbit ciliary artery.
Dr. Y. Dong, Department of Ophthalmology, School of Medicine, Kitasato University, Kanagawa, Japan
Classification:
11.3.4 Betablocker (Part of: 11 Medical treatment > 11.3 Adrenergic drugs)
6.11 Bloodflow measurements (Part of: 6 Clinical examination methods)
3.8 Pharmacology (Part of: 3 Laboratory methods)
