Effects of reduced oxygen tension on endothelium-dependent relaxation induced by acetylcholine differ in rabbit femoral artery and jugular vein

In intact rabbit femoral artery rings pre-contracted with phenylephrine, acetylcholine (ACh; 10(-9)-10(-6) M) produces endothelium-dependent relaxation, abolished after mechanical rubbing to remove the endothelium. The response to ACh was absent at low oxygen tension (less than or equal to 4 kPa) or in the presence of sodium cyanide (1 mM). Intact rabbit jugular veins relaxed to ACh in lower concentration than did the femoral artery, 10(-10)-10(-8) M; at sufficient ACh concentration the relaxation was complete. In veins with completely removed endothelium no relaxation to ACh occurred, and at concentrations above 3 x 10(-7) M the response was a contraction. The relaxation response to ACh of intact veins persisted during contraction at lower oxygen tension or in the presence of 1 mM sodium cyanide. In rubbed veins, cyanide consistently induced a transient contraction, which was absent in intact veins. The study demonstrates pronounced endothelium-dependent relaxation to ACh in a venous preparation, with a markedly lower sensitivity of the relaxation response to hypoxia than in a muscular artery of the same species.