3H-cimetidine and the H2-receptor

The H₂-antagonist cimetidine is widely employed in biochemical and pharmacological studies of the H₂-receptor. These studies include the use of ³H-cimetidine in radioligand binding experiments. Confirming our previous finding as to the unsuitability of this ligand in these types of investigations, we now report data showing the lack of correlation between the displacement of specific ³H-cimetidine binding and histamine stimulated adenylate cyclase activity, and the displacement of specific binding by imidazoles devoid of H₂-receptor activity. Results are also presented which question the use of copper ions in ³H-cimetidine binding studies. Our conclusions are discussed in relation to the work carried out by a number of laboratories where ³H-cimetidine is reported to label the H₂-receptor.