CARDIAC ALPHA-1-ADRENOCEPTOR DENSITIES IN DIFFERENT MAMMALIAN-SPECIES

1 alpha-1-Adrenoceptor densities were studied in cardiac membrane preparations from several mammalian species including human failing hearts under identical experiment conditions; the alpha-1-adrenoceptor antagonist, [H-3]-prazosin, was used as radioligand. End-stage heart failure (NYHA IV) in human hearts was due to idiopathic dilated cardiomyopathy. 2 The ventricular alpha-1-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. 3 A sufficient amount of right and left atrial tissue was obtained from rabbit, pig, calf, and man only. The alpha-1-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). 4 The equilibrium dissociation constant (K(D)) was similar in all species studied ranging from 0.047 +/- 0.006 to 0.063 +/- 0.007 nmol l-1. 5 It is concluded that differences in alpha-1-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.