Differential regulation of cardiac α‐ and β‐adrenoceptors by the sympathetic nervous system

1 The effects of depressed sympathetic function on the inotropic responses of the heart to sympathomimetic amines have been examined in rats immunized against nerve growth factor (NGF) 6 weeks prior to the isolation of cardiac tissues. 2 The activity of tyrosine hydroxylase in cervical sympathetic ganglia and the levels of noradrenaline in ventricular tissue were significantly reduced in NGF‐immunized rats. 3 Left atria and papillary muscles from NGF‐immunized rats were supersensitive to the β‐adrenoceptor agonist isoprenaline when compared with controls. 4 The responses of cardiac tissues to the α‐adrenoceptor agonist phenylephrine were unaffected by immunization. 5 These results support the hypothesis that cardiac β‐ but not α‐adrenoceptor sensitivity is regulated by the sympathetic nervous system.