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Responses of the internal carotid artery to different endogenous vasoconstrictor substances.

In order to study the action of serotonin (5-HT), noradrenaline (NA), hypertensin (HT), prostaglandins A1, B1 and E2 (PGA1, PGB1 and PGE2) and vasopressin (VP), internal carotid arteries were isolated in situ from both cerebral and general circulation and perfused continuously with oxygenated Ringers' bicarbonate solution. The order of potencies of the vasoactive substances when administered intra-arterially was: 5-HT greater than HT greater than PGE2- greater than PGB1 greater than NA. The relative duration of the constrictor effects was: 5-HT less than PGA1-less than HT and PGE2 less than PGB1 and NA less than VP. The relaxation index of these substances on the vascular wall was: 5-HT less than PGE2 less than HT less than PGB1-less than NA less than PGA1 less than VP. Some of these substances, specifically PGB1, PGE2 and VP, frequently caused a residual constriction of the smooth muscle following their dilator effect. The role of these vasoactive substances in the development of vasospasm is discussed.