SEROTONIN (5HT) AND ITS ANTAGONISTS: INVOLVEMENT IN THE CARDIOV ASCULAR SYSTEM

The cardiovascular actions of serotonin and its antagonists are reviewed with a view to clarifying whether serotonin has a role in blood pressure control through actions on the peripheral vasculature. Serotonin has complex actions in the heart and vasculature but none of these actions is completely understood. There is no doubt, however, that serotonin has extensive interactions with the sympathetic nervous system. The nature of the serotonin receptor is also discussed. There is extensive evidence that more than one type of serotonin receptor exists. Biochemical studies in brain homogenates have delineated two sub-populations of serotonin receptors, named 5HT1 and 5HT2. It is not clear whether the same receptor types exist in the vasculature but various actions of serotonin on the vasculature have tentatively been ascribed to actions on 5HT1- and 5HT2-type receptors. It is clear that there is some functional overlap between serotonin-receptors and alpha-adrenoceptors. The mechanism by which this overlap could occur is unknown although we suggest it may result from a physical overlap of serotonin receptors and alpha-adrenoceptors. Compounds which antagonize serotonin have provided the means for investigating serotonin receptors but have not clarified the role of serotonin in blood pressure control; certainly they have comparatively little effect on blood pressure and this may simply reflect the lack of free circulating serotonin. In animal studies the new serotonin antagonist ketanserin appears to lower blood pressure via alpha-adrenoceptor blockade.