Dual effects of alpha-adrenoceptor agonist on contractility of mice isolated atria.
Contractility responses of mice atria to alpha-adrenergic agonists (methoxamine and clonidine) were studied. The alpha-adrenergic agonists increased the rate of force development (dF/dt) and decreased contractile frequency. The positive inotropic effect was mediated through cardiac alpha-adrenoceptors, while the negative chronotropic effect involved parasympathetic activation. Blockers of phospholipase C inhibited both the positive inotropic and the negative chronotropic effects of the alpha-adrenergic agonists. Inhibitors of phospholipase A2 and cyclooxygenase activity attenuated the positive inotropic effect of the agonists without modifying the negative chronotropic effect.
D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D016861:Cyclooxygenase Inhibitors; D003864:Depression, Chemical; D006325:Heart Atria; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D008729:Methoxamine / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009200:Myocardial Contraction / Q000187:drug effects*; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D013268:Stimulation, Chemical; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D016861:Cyclooxygenase Inhibitors; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D008729:Methoxamine; D003000:Clonidine