The WKY/NCrj rat strain is considered to be a good animal model for hypertrophic cardiomyopathy (HCM). The purpose of this study was to examine the beta-adrenergic receptor/adenylate cyclase system in the cardiac ventricles of these rats. beta-adrenergic receptor density (Bmax) in the right ventricle (RV) was higher in WKY/NCrj than in Wistar rats. In contrast, Bmax in the interventricular septum (IVS) was lower in WKY/NCrj than in Wistar rats. Isoproterenol-stimulated adenylate cyclase activity in cardiac ventricular slices showed that changes corresponded to the changes of Bmax in every type of studied cardiac ventricle. The intracellular adenylate cyclase pathway (GTP gamma S-, NaF- and forskolin-stimulated adenylate cyclase activity in cardiac ventricular particulate fraction) did not differ between WKY/NCrj and Wistar rats in any region of the cardiac ventricles. Catecholamine levels tended to be low in the RV and to increase in the IVS of WKY/NCrj rats. Our results suggest that the activity of the beta-adrenergic receptor/adenylate cyclase system varies in different cardiac ventricles of the WKY/NCrj rat model for HCM.