Peripheral 5-hydroxytryptamine receptors and their classification.

A critical appraisal of the literature on peripheral 5-HT receptor classification indicates that only two types have been definitively characterised. One of these appears to be the same as the 5-HT2 ligand binding site, identified in brain tissue. The other is similar to Gaddum and Picarelli's "M" receptor and appears to have no equivalent binding site. Both these types appear to have been sufficiently characterised to be worthy of naming though no agreed system is available. At least two other types of 5-HT receptor appear to exist on pharmacological grounds, but even if a system of nomenclature had been agreed, they have not yet been adequately characterised.