L-NAME- and U 46619-induced contractions in isolated porcine ciliary arteries verses vortex veins

Purpose: To investigate contractions evoked by the thromboxane A, analog U4 6619 and by the inhibitor of nitric oxide formation NG-nitro-L-arginine met hyl eater (L-NAME) in isolated porcine ciliary arteries and vortex veins. Material and Methods: In a myograph system (for isometric forces measuremen t), vessels were exposed (at different Levels of wall tension) to 100 mM po tassium chloride (I(CI). At their optimal tension, vessels were exposed tin a cumulative manner) to increasing concentrations of U 46619 (0.1 nM-1 muM ) in the absence or in the presence of L-NAME (0.1 mM). Contractions were e xpressed in mN or in percent of a 100 mM KCI-induced contraction. Results: Optimal tension was higher in arteries (7 mN) than in veins (3mN). Maximal contractions induced by KCI were stronger in arteries (24.4 +/- 3. 6 mN; n = 8) than In veins (1.8 +/- 0.2 mN; n = 8). In contrast, maximal co ntractions evoked by U 46619 were proportionally higher (p<0.001) in veins (178.3 <plus/minus> 8.9%; n = 8) than in arteries (108.4 +/- 2.6%; n = 5) a nd were not significantly affected by L-NAME. Sensitivity to U 46619 was no t significantly different between arteries (pD(50) = 7.7 +/- 0.1) and veins (pD(50) = 7.9 +/- 0.1). In quiescent vessels, L-NAME evoked contractions t hat were higher (p<0.007) in veins (43 <plus/minus> 7.9%: n = 13) than in a rteries (7.5 +/- 1.7 %; n = 10). Conclusions: When compared with KCI-induced contractions, contractions evok ed by U 46619 or L-NAME are proportionally higher in porcine vortex veins t han in ciliary arteries.