Hypoxic contraction in canine basilar arteries: role of endothelium

The effect was studied of severe hypoxia (partial pressure of oxygen below 20 mm Hg) on the tone of isolated canine basilar arterial rings with and without endothelium. Short-lasting exposure (8 min) to hypoxia induced a pronounced contraction that did not differ in vessels with and without endothelium. The hypoxia-induced changes of vessel tone were reproducible in 3 consecutive episodes of hypoxia interspaced by 45 min of control oxygenation. Reintroduction of oxygen induced a posthypnoxic relaxation in preparations without endothelium and a posthypoxic contraction in part (5 of 15) of the arteries with endothelium. The hypoxic contraction was not influenced by the cyclooxygenase inhibitor indomethacin and the thromboxane A2 receptor antagonist BM 13.505 while the posthypoxic response was diminished by both inhibitors. The Ca(++)-entry blocker D600 abolished both hypoxic and posthypoxic contractions completely.