Different Influence of Endothelium in the Mechanical Responses of Human and Cat Isolated Cerebral Arteries to Several Agents

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Abstract
The present work was undertaken to elucidate the role of the vascular endothelium in the changes of isometric tension elicited by different compounds in isolated cylinders of human and cat cerebral arteries and cat pulmonary arteries. Endothelium removal by rubbing significantly reduced the relaxing response to acetylcholine (ACh) of isolated segments of all the arteries. The same treatment did not modify the contraction elicited by 5-hydroxytryptamine (5-HT) in the human and cat cerebral segments but increased the contractile effect of the amine in cat pulmonary arteries. The mechanical responses to vasopressin, ATP and adenosine in isolated segments of cat cerebral arteries were unaffected after removing the endothelial layer. L-Arginine, but not D-arginine (10−5 M), enhanced significantly the relaxation induced by increasing doses of ACh in unrubbed cat cerebral arteries whereas it did not modify the response to ACh in rubbed ones. However, L-arginine had no effect on the dose-response curve to 5-HT in both kinds of preparation and did not change the tone in precontracted unrubbed cat cerebral segments. These results suggest that the endothelium of the cerebrovascular bed plays a minor role in regulating the mechanical response induced by several vasoactive agents, although it retains its ability to produce an endothelium-derived relaxing factor.