title: [Alpha-adrenoceptors in the myocardium: incidence and functional significance].
abstract: Alpha-adrenoceptors mediating positive inotropic effects are well established in the heart of various species including human heart. The mechanism by which alpha-adrenoceptor stimulation increases force of contraction is not known. cAMP is unlikely to be involved as a mediator. Evidence has been presented that an increase in magnitude and duration of the slow Ca++ inward current may be partly responsible for the positive inotropic effect. In addition, stimulation of alpha-adrenoceptors may increase Ca++ sensitivity of the contractile proteins. Stimulation of alpha-adrenoceptors by endogenous catecholamines may serve as a reserve mechanism under various conditions of impaired beta-adrenergic influence, e.g. hypothyroidism, bradycardia or ischemia. Furthermore, alpha-adrenoceptors may be involved in the genesis of reperfusion arrhythmias in ischemic heart.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003327:Coronary Disease / Q000503:physiopathology; D000242:Cyclic AMP / Q000502:physiology; D006801:Humans; D006980:Hyperthyroidism / Q000503:physiopathology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000032:analysis*; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000032:analysis / Q000502:physiology; D013268:Stimulation, Chemical; D013566:Sympathomimetics / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D013566:Sympathomimetics; D010656:Phenylephrine; D000242:Cyclic AMP; D002118:Calcium
vernacular_title: Alpha-Adrenozeptoren am Myokard: Vorkommen und funktionelle Bedeutung.