OBJECTIVE: The aim was to characterise the transmural distribution of beta adrenergic receptors in failing myocardium in cardiomyopathy. METHODS: Using a quantitative autoradiographic technique with 125I-cyanopindolol (ICYP), the density and transmural distribution of beta adrenergic receptors were compared between eight cardiomyopathic BIO 14.6 Syrian hamsters with heart failure and six normal age matched controls (BIO 14.6HAM). RESULTS: Binding of ICYP to transmural slices of hamster myocardium was rapid, saturable, stereoselective, and displaceable by antagonists. The binding isotherm showed a significant increase in the total tissue content of beta adrenergic receptors in the failing myocardium of cardiomyopathic hamsters: 15.3(SEM 1.6) fmol.mg-1 protein v 9.4(1.2) fmol.mg-1 protein in normal myocardium of control hamsters (p < 0.05). There was no difference in receptor affinity. Quantitative autoradiography showed regional heterogeneity of beta adrenergic receptors in cardiomyopathic hamsters, with an increase of beta adrenergic receptor density in the septal and subendocardial regions. In addition, the regions with increased interstitial fibrosis corresponded to the sites of increased beta adrenergic receptor density. CONCLUSIONS: The transmural distribution of beta adrenergic receptor is heterogeneous in the failing myocardium of cardiomyopathic hamsters and an increased beta adrenergic receptor density may be associated with the development of cardiomyopathy.
OBJECTIVE: The aim was to characterise the transmural distribution of beta adrenergic receptors in failing myocardium in cardiomyopathy. METHODS: Using a quantitative autoradiographic technique with 125I-cyanopindolol (ICYP), the density and transmural distribution of beta adrenergic receptors were compared between eight cardiomyopathic BIO 14.6 Syrian hamsters with heart failure and six normal age matched controls (BIO 14.6HAM). RESULTS: Binding of ICYP to transmural slices of hamster myocardium was rapid, saturable, stereoselective, and displaceable by antagonists. The binding isotherm showed a significant increase in the total tissue content of beta adrenergic receptors in the failing myocardium of cardiomyopathic hamsters: 15.3(SEM 1.6) fmol.mg-1 protein v 9.4(1.2) fmol.mg-1 protein in normal myocardium of control hamsters (p < 0.05). There was no difference in receptor affinity. Quantitative autoradiography showed regional heterogeneity of beta adrenergic receptors in cardiomyopathic hamsters, with an increase of beta adrenergic receptor density in the septal and subendocardial regions. In addition, the regions with increased interstitial fibrosis corresponded to the sites of increased beta adrenergic receptor density. CONCLUSIONS: The transmural distribution of beta adrenergic receptor is heterogeneous in the failing myocardium of cardiomyopathic hamsters and an increased beta adrenergic receptor density may be associated with the development of cardiomyopathy.