The important role of α₁-adrenergic receptors in the genesis of cardiac arrhythmias in ischemia and during reperfusion<sup>1Corr P.B., Crafford W.A. Enhanced α-adrenergic responsiveness in ischemic myocardium; role of a–adrenergic blockade Am Heart J 1981 ;  102 : 605-612 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti,2Hamra R., Rosen M.R. α–adrenergic receptor stimulation during simulated ischemia and reperfusion in canine cardiac Purkinje fibers Circulation 1988 ;  78 : 1495-1502

Cliccare qui per andare alla sezione Riferimenti</sup> has recently been elucidated. On the other hand, α₁-adrenergic modulation of cardiac rhythm has promoted interest in myocardial α₁-adrenoceptor research. The chronotropic action of α₁-adrenergic stimulation is usually reported as inhibitory rather than excitatory.<sup>3Rosen M.R., Hordof A.J., Ilvento J.P., Danilo P. Effects of adrenergic amine on electrophysiological properties and automaticity of neonatal and adult canine Purkinje fibers; evidence for alpha– and beta–adrenergic actions Circ Res 1977 ;  40 : 390-400 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> However, in some species and in certain tissues, the positive chronotropic action of α₁-adrenergic stimulation has also been reported. Moreover, there is an important developmental component to the α₁-adrenergic receptor-effector system. Although α₁-adrenergic stimulation decreases automaticity in the human atrium and in the ventricular conducting system of the adult rat,<sup>4Drugge E.D., Rosen M.R., Robinson R.B. Neuronal regulation of the development of the α-adrenergic chronotropic response in the rat heart Circ Res 1985 ;  57 : 415-423 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti,5Mary-Rabine L., Hordof A.J., Bowman F., Malm J.R., Rosen M.R. Alpha and betaadrenergic effects on human atrial specialized conducting fibers Circulation 1978 ;  57 : 84-90 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> an increase in automaticity brought about by α₁ adrenergic stimulation was reported in isolated neonatal canine Purkinje fibers.<sup>6Reder R.F., Danilo P., Rosen M.R. Developmental changes in alpha adrenergic effects on canine Purkinje fiber automaticity Dev Pharmacol Ther 1984 ;  7 : 94-108 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> These findings suggest that the chronotropic response of cardiac tissues to α₁-adrenergic stimulation changes from excitatory to inhibitory during development. This study clarifies the effect of α₁-adrenergic stimulation on human sinus node automaticity, especially in relation to age.