Endothelium and asymmetrical responses of the coronary arterial wall.
Changes in isometric tension due to intra- or extraluminal addition of vasoactive agents were determined in isolated perfused segments of canine left circumflex coronary artery. Segments denuded of endothelium were more sensitive to the contractile action of 5-hydroxytryptamine and potassium during intraluminal addition. In segments with intact endothelium, the sensitivity to intraluminal, but not extraluminal, 5-hydroxytryptamine was decreased in comparison to denuded segments; that to potassium was unchanged. In segments with intact endothelium contracted with prostaglandin F2 alpha, intraluminal, but not extraluminal, acetylcholine, adenosine diphosphate, or thrombin caused relaxation. Intraluminal 5-hydroxytryptamine and aggregating platelets caused relaxation or attenuated contractions in a majority of vessels studied; extraluminal addition caused only contractions. Thus the endothelium is responsible for opposite smooth muscle responses to intra- versus extraluminal vasoactive substances released from aggregating platelets. During intraluminal thrombosis the endothelium may inhibit smooth muscle contraction by responding to 5-hydroxytryptamine and adenosine diphosphate released from platelets and to thrombin; where the endothelium is damaged, the luminal aspect of the blood vessel wall, which is more sensitive to 5-hydroxytryptamine, may become the site of coronary spasm.
D000109:Acetylcholine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001158:Arteries; D001792:Blood Platelets; D003331:Coronary Vessels / Q000502:physiology*; D004285:Dogs; D004727:Endothelium / Q000502:physiology; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation; D011188:Potassium / Q000494:pharmacology; D011460:Prostaglandins F / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology
D011460:Prostaglandins F; D012701:Serotonin; D000244:Adenosine Diphosphate; D013917:Thrombin; D000109:Acetylcholine; D011188:Potassium