During an in-house database screen, we identified S-(2-guanidylethyl)-isothiourea as a high affinity agonist for the histamineH4 receptor, with a 33-fold selectivity over the histamine H3 receptorand negligible affinity for the other histamine receptor subtypes. Thisnonimidazole ligand is introduced as a useful and complementarypharmacological tool that enables further unraveling of the physiologicalroles of the H4 receptor.
