Quantification of H2-agonism by clonidine and dimaprit in an adenylate cyclase assay

Agents Actions. 1985 Apr;16(3-4):222-6. doi: 10.1007/BF01983145.


In homogenates of guinea-pig ventricle clonidine and dimaprit both stimulate adenylate cyclase and exhibit "bell-shaped' E/[A] curves. The two properties (stimulatory and inhibitory) could be resolved using a theoretical model assuming a "down line' auto-inhibitory mechanism. In the case of clonidine a further depressive property could be seen in the presence of high concentrations of the selective H2-receptor antagonist tiotidine which is not explicable in terms of this model. The results suggest that clonidine has a direct agonistic effect on H2-receptors in guinea-pig heart. However, like dimaprit, clonidine appears to be a partial agonist because its expression is confounded by a secondary inhibitory property(ies).

MeSH terms

  • Adenylyl Cyclases / analysis*
  • Animals
  • Cimetidine / analogs & derivatives
  • Cimetidine / pharmacology
  • Clonidine / pharmacology*
  • Dimaprit
  • Guinea Pigs
  • Histamine / pharmacology
  • In Vitro Techniques
  • Myocardium / enzymology
  • Receptors, Histamine / drug effects*
  • Receptors, Histamine H2 / drug effects*
  • Thiourea / pharmacology*


  • Receptors, Histamine
  • Receptors, Histamine H2
  • Cimetidine
  • Histamine
  • Adenylyl Cyclases
  • tiotidine
  • Thiourea
  • Clonidine
  • Dimaprit