Tritium-Labeled N1-[3-(1H-imidazol-4-yl)propyl]-N2-propionylguanidine ([3H]UR-PI294), a High-Affinity Histamine H3 and H4 Receptor Radioligand

This study reports the synthesis and pharmacological characterization of tritium-labeled N-1-[3-(1H-imidazol-4-yl)propyl]-N-2-propionylguanidine ([H-3]UR-PI294), a novel and readily accessible radioligand for the human histamine H-3 receptor (hH(3)R) and H-4 receptor (hH(4)R). The radioligand displays high affinity for both histamine receptor subtypes (K-D (hH(3)R) = 1.1 nm, K-D (h H4R) = 5.1 nM) and is shown to be a valuable pharmacological tool for the determination of hH(3)R and hH(4)R affinities.