Sustained Anoxia Decreases Contraction and Endothelium-Dependent and Independent Relaxation in Rat Aortic Rings

Abstract

Exposure of precontracted vascular tissues to anoxia in vitro causes a rapid but short lasting additional contraction of vascular smooth muscle. To determine the effect of sustained anoxia on vascular reactivity, quiescent rat aortic rings were equilibrated at 37°C under 95% O2 (normoxia) or 95% N2 (anoxia) for 15 min. The rings were then contracted with norepinephrine (NE) or the TxA2-endoperoxide analog 1146,619. The response of aortic rings to the endothelium-dependent vasorelaxant stimuli acetylcholine (ACh) and calcium ionophore A23,187, the endothelium-independent stimuli nitroglycerin (NTG) and sodium nitroprusside (SNP) and the nitric oxide-independent stimulus isoproterenol (ISO) was also examined. Vascular contraction was markedly decreased in anoxic rings (P < 0.01 versus normoxic rings) in response to both NE and U46.619 and was not modified on treatment with indomethacin, L-NMMA or Nω-L-arginine. Relaxation of anoxic rings was also markedly impaired (P < 0.01) in response to the endothelium-d...