RESPONSE OF ISOLATED CAT MIDDLE CEREBRAL-ARTERY TO PLATELETS - EFFECT OF ENDOTHELIUM REMOVAL

1. Platelets induced an endothelium-independent contraction in isolated cat middle cerebral artery under resting conditions. In precontracted segments they evoked an endothelium-dependent contraction followed by a relaxation. 2. The contraction induced by serotonin was unaffected by endothelium removal either in the absence or in the presence of a previous tone. 3. The contractile response to platelets and serotonin under resting tension was blocked in the same way by ketanserin, methysergide or cyproheptadine. 4. After adding the platelets, serotonin could be measured in the bath medium. 5. These results suggest that the endothelium plays a minor role in the contraction induced by platelets, which is partly due to serotonin release.