Induction of iNOS in human saphenous veins

E.coli lipopolysacharide (LPS) stimulates inducible nitric oxide synthase (iNOS) in animal vascular smooth muscle but iNOS has not been documented in human saphenous veins. Previous investigators failed to demonstrate iNOS in human saphenous veins with LPS stimulation. We exposed human saphenous veins to E. coli LPS (100μgm/ml) for 20hr and suspended in organ chambers. Veins were contracted with a maximum dose of KCl (80mM). There was no difference in KCl contraction in either controls or LPS veins (1.0±0.2gm vs 1.7±0.7gm, n=5, t-test). Veins were then contracted with norepinephrine (NE, 10^-9-10^-5M). LPS veins had a reduced contraction to NE, both developed tension and KCl-normalized tension were reduced compared to controls (n=5, P<0.05, ANOVA). Indomethacin (10^-5M) pretreatment did not alter the reduced NE contraction in LPS veins (n=5), but L-NMMA (10^-4M) pretreatment attenuated the contraction differential so LPS vessels exposed to NE contracted similar to controls. Tetraethylammonium chloride (TEA, 10^-3M) pretreatment likewise reversed the contraction differential (n=5), demonstrating reversal of nitric oxide hyperpolarization. This study demonstrates induction of iNOS in human saphenous veins for the first time, contradicting previous investigations.