The effect of NO donors on bovine retinal small arteries and posterior ciliary arteries.

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.