Differential regulation of cardiac alpha- and beta-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 beta-adrenoceptor agonist isoprenaline when compared with controls. 4. The responses of cardiac tissues to the alpha-adrenoceptor agonist phenylephrine were unaffected by immunization. 5. These results support the hypothesis that cardiac beta- but not alpha-adrenoceptor sensitivity is regulated by the sympathetic nervous system.