The interaction of antidepressant drugs with enteric 5-HT7 receptors.
In this study the functional interaction of the antidepressant drugs amitriptyline, mianserin, maprotiline, imipramine, fluoxetine and the putative antidepressant drug flibanserin has been studied on 5-HT7-mediated responses to 5-carboxamidotryptamine (5-CT) in the guinea-pig ileum. 5-CT induced a concentration-dependent inhibition of the contractile response to substance P (100 nM). Except for fluoxetine and flibanserin, all the antidepressants antagonized by different degrees the 5-CT inhibitory response with the following rank affinity order: mianserin > maprotiline > imipramine > amitriptyline. Mianserin was the only antidepressant to show a profile of competitive antagonism at 5-HT7 receptors in a tenfold range of concentrations (0.1-1 microM), with an affinity (pA2) value of 8.1 +/- 0.6. The antagonism of the other antidepressants was not concentration-dependent (amitriptyline) or was associated with slight or moderate reduction of the maximal 5-CT response (imipramine or maprotiline). The apparent affinity (pKB) values were: amitriptyline, 7.0 +/- 0.2; maprotiline, 7.3 +/- 0.6; imipramine, 7.2 +/- 0.4. Our results show that various antidepressant drugs belonging to different chemical classes behave as antagonists at enteric 5-HT7 receptors through competitive or allosteric mechanisms. This evidence extends our previous findings demonstrating the interaction of antidepressants with other 5-HT receptors, namely 5-HT3 and 5-HT4 receptors.
Lucchelli
A
A
Department of Experimental and Applied Pharmacology, School of Pharmacy, University of Pavia, Italy. adlu@unipv.it
Santagostino-Barbone
M G
MG
D'Agostino
G
G
Masoero
E
E
Tonini
M
M
D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*
D000928:Antidepressive Agents; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; C104425:serotonin 7 receptor; D012701:Serotonin; C047087:5-carboxamidotryptamine