FIGURE 11-3 Local influences of platelet 5-HT. Aggregation triggers the release of 5-HT stored in platelets. Local actions of 5-HT include feedback actions on platelets (shape change and accelerated aggregation) mediated by 5-HT2A receptors, stimulation of NO production mediated by 5-HT1-like receptors on vascular endothelium, and contraction of vascular smooth muscle mediated by 5-HT2A receptors. These influences act in concert with many other mediators (not shown) to promote thrombus formation and hemostasis. See Chapter 54 for details of adhesion and aggregation of platelets and factors contributing to thrombus formation and blood clotting.
on vagus nerve endings elicits the Bezold-Jarisch reflex, causing bradycardia and hypotension. The local response of arterial blood vessels to 5-HT also may be inhibitory, the result of stimulated NO and prostaglandin synthesis and blockade of NE release from sympathetic nerves. On the other hand, 5-HT amplifies the local constrictor actions of NE, Angll, and histamine, which reinforce the hemostatic response to 5-HT.
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