Effects of antidepressants on histamine H1 and muscarinic acetylcholine receptors in guinea-pig ileum.

The properties of some tricyclic and non-tricyclic antidepressants on antagonist histamine H1 and muscarinic acetylcholine receptors have been evaluated on guinea-pig ileum. They act like competitive antagonists on histamine H1 receptors. Some of them show a competitive antagonism and others a non-competitive antagonism on muscarinic acetylcholine receptors. A few of them are very potent antagonists on histamine H1 and/or muscarinic acetylcholine receptors, while others, especially the non-tricyclic antidepressants, have a small potency. All antidepressants have a higher histamine H1 activity than muscarinic acetylcholine activity. These results cannot explain the therapeutic effect of these drugs, but they can account for some side effects and drug interactions.