Specific binding of 3H-tiotidine to histamine H2 receptors in guinea pig cerebral cortex

Although the H 2 subclass of histamine receptor has been revealed by classical pharmacological approaches 1,2 , the direct identification of this adenylate cyclase-linked receptor has, despite much effort, remained elusive. Initial studies using 3 H-metiamide and 3 H-histamine 3,4 and, subsequently, work from our own laboratory and others using 3 H-cimetidine 5–8 and 3 H-ranitidine 9 in various tissues, has shown the unsuitability of these ligands for labelling the H 2 receptor. We report here our results using 3 H-tiotidine, a more potent H 2 -antagonist than either cimetidine or ranitidine 10 , and show that this ligand meets the criteria for labelling the H 2 receptor in guinea pig cerebral cortex membranes.