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

Purpose: To investigate contractions evoked by the thromboxane A 2 analog U 46619 and by the inhibitor of nitric oxide formation N G -nitro-L-arginine methyl ester (L-NAME) in isolated porcine ciliary arteries and vortex veins. Material and Methods: In a myograph system (for isometric forces measurement), vessels were exposed (at different levels of wall tension) to 100 mM potassium chloride (KCI). At their optimal tension, vessels were exposed (in a cumulative manner) to increasing concentrations of U 46619 (0.1 nM - 1 μM) in the absence or in the presence of L-NAME (0.1 mM). Contractions were expressed in mN or in percent of a 100 mM KCI-induced contraction. Results: Optimal tension was higher in arteries (7 mN) than in veins (3 mN). 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 contractions evoked by U 46619 were proportionally higher (p < 0.001) in veins (178.3 ± 8.9%; n=8) than in arteries (108.4 ± 2.6%; n=5) and were not significantly affected by L-NAME. Sensitivity to U 46619 was not 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 that were higher (p < 0.001) in veins (43 ± 7.9%; n = 13) than in arteries (7.5 ± 1.7 %; n = 10). Conclusions: When compared with KCI-induced contractions, contractions evoked by U 46619 or L-NAME are proportionally higher in porcine vortex veins than in ciliary arteries.