Endothelial modulation of contractions caused by oxyhemoglobin and NG-nitro-L-arginine in isolated dog and monkey cerebral arteries.

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Abstract
Oxyhemoglobin is a key substance in provoking cerebral vasospasm and a scavenger of nitric oxide. The present study was designed to determine whether suppression of the action of endothelium-derived nitric oxide is involved in oxyhemoglobin-induced cerebroarterial contraction. Dog and monkey cerebral artery strips with and without endothelium were immersed for isometric tension recording in modified Ringer-Locke solution aerated with 95% oxygen and 5% carbon dioxide. NG-nitro-L-arginine, a nitric oxide synthase inhibitor, produced concentration-related contraction that was greater in the strips with intact endothelium than in those denuded of endothelium. The D-enantiomer caused no or only a slight contraction. In the presence of NG-nitro-L-arginine, oxyhemoglobin elicited additional contraction that is comparable to or even greater than that obtained in the absence of the inhibitor. The oxyhemoglobin-induced contraction was attenuated by endothelium denudation. Inhibition of the basal release of nitric oxide from endothelium results in dog and monkey cerebral arterial contraction. However, the inhibition of nitric oxide action is not a major mechanism involved in oxyhemoglobin-induced contraction; other mechanisms, such as the release of prostanoids, appear to be important.