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Abstract
PURPOSE: This study was designed to investigate the effect of nitric oxide (NO) donors on isolated bovine retinal and ciliary arteries. METHODS: Bovine retinal and short posterior ciliary arteries were mounted on a dual-wire myograph for isometric tension recordings. The relaxation induced by increasing concentrations of the following NO donors was compared: 0.1 nM to 10 microM nitroglycerin, 0.1 nM to 0.1 mM isosorbide dinitrate, 0.1 microM to 1 mM sodium nitrite, 1 nM to 0.1 mM sodium nitroprusside, and 0.1 microM to 10 microM N-carboxy-3-morpholinosydnonimine ethyl ester (Sin-1) applied to vessels after precontraction with 1 microM thromboxane A2 mimetic (U46619). The effects of 1 microM and 10 microM nitric oxide; 1 mM 8-bromo-cyclic guanosine monophosphate (cGMP), a stable cGMP analogue; and 0.1 mM papaverine were also studied. RESULTS: The NO donors elicited a swift and concentration-dependent relaxation of the ciliary arteries. The retinal small arteries were resistant to these drugs. Even at high concentrations, only moderate relaxation was elicited. The cGMP analogue 8-bromo-cGMP also induced significantly more relaxation of the posterior ciliary arteries than of the retinal small arteries. Papaverine almost completely relaxed both vessels. CONCLUSIONS: Nitric oxide donors exert only a moderate relaxing effect on retinal arteries. A weak influence of cGMP-dependent mechanisms on the retinal arterial tone is thought to be responsible.