5-Hydroxytryptamine and beta-adrenoceptors in rat isolated atria.
The positive chronotropic effect of a high concentration of 5-hydroxytryptamine (5-HT) in rat isolated atria results mainly from a tyramine-like mechanism and is linked to an increase in cAMP production by an indirect stimulation of beta-adrenoceptors. Using this preparation, we have compared the action of tyramine and 5-HT. The tyramine (0.15 microM)-induced increase in atrial rate was suppressed by atenolol (a beta 1-blocking drug) and by nadolol (a beta 1 beta 2-blocker), while the positive chronotropic effect of 5-HT was reduced by atenolol and suppressed by nadolol. The 5-HT-induced elevation in cAMP was unchanged in the presence of atenolol and abolished by nadolol. The involvement of beta 2-adrenoceptors in the effects of 5-HT could result from competition between 5-HT and noradrenaline at the beta 1-adrenoceptors that results in a fixation of noradrenaline on beta 2-adrenoceptors.
Davy
M
M
Laboratoire de Pharmacologie, Faculté de Pharmacie, Université Paris-Sud, Châtenay-Malabry, France.
Grandcourt
O
O
Midol-Monnet
M
M
Cohen
Y
Y
D018663:Adrenergic Agents / Q000494:pharmacology*; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D006325:Heart Atria / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D014439:Tyramine / Q000494:pharmacology*
D018663:Adrenergic Agents; D011943:Receptors, Adrenergic, beta; D012701:Serotonin; D000242:Cyclic AMP; D014439:Tyramine