Cardiac α1‐adrenoceptor densities in different mammalian species

Abstract

α 1‐Adrenoceptor densities were studied in cardiac membrane preparations from several mammalian species including human failing hearts under identical experiment conditions; the α1‐adrenoceptor antagonist, [3H]‐prazosin, was used as radioligand. End‐stage heart failure (NYHA IV) in human hearts was due to idiopathic dilated cardiomyopathy. The ventricular α1‐adrenoceptor densities were not significantly different in guinea‐pig, mouse, pig, calf, and man (11 to 18 fmol mg−1 protein) but about 5 to 8 fold smaller than in rat (about 90 fmol mg−1 protein). Right and left ventricular receptor densities were similar in these species. A sufficient amount of right and left atrial tissue was obtained from rabbit, pig, calf, and man only. The α1‐adrenoceptor densities in both atria of these species were found to be at the detection limit of the method used (less than 8 fmol mg−1 protein). The equilibrium dissociation constant (KD) was similar in all species studied ranging from 0.047 ± 0.006 to 0.063 ± 0.007 nmol l−1. It is concluded that differences in α1‐adrenoceptor density between atria and ventricles may exist in mammalian species. The exceptionally high density of these receptors in rat ventricles seem to be a particular feature in these animals. 1992 British Pharmacological Society