/-Adrenergic Supersensitivity of the Transplanted Human Heart Is Presynaptic in Origin

An increase in cardiac P-adrenergic sensitivity or 8-receptor density or both has been described in several animal species after denervating the heart. The transplanted human heart is also denervated and, therefore, may exhibit supersensitivity to /3-adrenergic agonists and an increase in .3-adrenergic receptor density. In 16 patients examined 1-3 months after orthotopic cardiac transplantation, /3-adrenergic receptor density measured by [t211]iodocyanopindolol binding in endomyocardial biopsy specimens was not significantly different in transplant recipients compared with normal controls (transplant=1,429±199, control=1,728±263 fmol/g wet wt; p=NS). However, when normalized to Lowry protein, the ['25lliodocyanopindolol in ,8-adrenergic receptor density in biopsy tissue from transplant recipients was significantly lower than in tissue from controls (transplant=58.1+6.2, control=93.5+13.4 fmol/g Lowry protein;