Collateral arterial tree and responses to serotonin.

Growing collateral arterial blood vessels are super-sensitive to serotonin. Advanced atherosclerosis causes platelet activation, and activated platelets release sufficient serotonin that collateral arterial spasm occurs as a response. The development of ketanserin, the 5-HT2-receptor blocker, has both identified the receptor responsible for the arterial spasm and provided new approaches to treatment.