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.