Abstract
The study concerned effects of ketanserin and a new 5-HT 2 receptor antagonist, Wal 1307, on the responses to 5-hydroxytryptamine (5-HT) in the porcine common carotid vascular bed. More than 80% of the total carotid blood flow (208 ± 18 ml; n = 12) bypassed the tissues via arteriovenous anastomoses. Intracarotid infusions of 5-HT (2 μg·kg −1·min −1) reduced the total carotid blood flow by about 50% and arteriovenous anastomotic flow by 85% but extracerebral tissue (nutrient) blood flow more than tripled. The cerebral component did not change. Thus, 5-HT appears to constrict large conducting arteries and arteriovenous anastomoses but dilates arterioles. Ketanserin and Wal 1307 did not affect carotid blood flow distribution but completely blocked the amine-induced reduction of total carotid blood flow. The constriction of arteriovenous anastomoses was only slightly reduced but the 5-HT-induced arteriolar vasodilation was enhanced. We conclude that vasoconstriction in the main trunk of the carotid artery and, to a smaller degree, in the arteriovenous anastomoses and arterioles, is mediated by 5-HT 2 receptors. The major part of the constriction of arteriovenous anastomoses and arteriolar dilation elicited by 5-HT is, however, not mediated by 5-HT 2 receptors. It is argued that these ‘atypical’ 5-HT receptors may be related to 5-HT 1 binding sites.
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