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 o xide (NO) donors on isolated bovine retinal and ciliary arteries. METH ODS. Bovine retinal and short posterior ciliary arteries were mounted on a dual-wire myograph for isometric tension recordings. The relaxati on induced by increasing concentrations of the following NO donors was compared. 0.1 nM to 10 mu M nitroglycerin, 0.1 nM to 0.1 mM isosorbid e dinitrate, 0.1 mu M to 1 mM sodium nitrite, I nM to 0.1 mM sodium ni troprusside, and 0.1 mu M to 10 mu M N-carboxy-3-morpholinosydnonimine ethyl ester (Sin-l) applied to vessels after precontraction with 1 mu M thromboxane A(2) mimetic (U46619). The effects of 1 mu M and 10 mu M 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 relaxatio n of the ciliary arteries. The retinal small arteries were resistant t o these drugs. Even at high concentrations, only moderate relaxation w as 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. CO NCLUSIONS. Nitric oxide donors exert only a moderate relaxing effect o n retinal arteries. A weak influence of cGMP-dependent mechanisms on t he retinal arterial tone is thought to be responsible.