Propranolol therapy in experimental heart failure in rabbits improves cardiac response to catecholamines without beta-adrenoceptor up-regulation.

Beta-blockade has been shown to improve cardiac response to catecholamines in heart failure but cellular mechanisms of the improvement are unknown. The effect on left ventricular function of a 14 day propranolol treatment was studied in seven treated and eight non-treated rabbits with experimental heart failure. All animals were subjected to a volume (aortic insufficiency) plus pressure (aortic constriction) overload and were instrumented with a left ventricular catheter and ultrasonic crystals measuring anteroposterior left ventricular diameter. Beta-adrenoceptors were measured using 125I-Cyanopindolol in crude membranes. With isoproterenol, the heart rate was slower in treated rabbits than in non-treated rabbits (p < 0.005) and isoproterenol increased more systolic diameter shortening in treated than in non-treated rabbits (p < 0.05). With norepinephrine, for matched pressures, % delta D increased in the treated group but it did not change in the non-treated group. This improvement of ventricular function was due, in a large part, to an increased diastolic response to norepinephrine: end-diastolic diameter increased in the treated group but not in the non-treated group. In contrast with the improved ventricular response to catecholamines, beta-adrenergic receptor density in the treated group was identical to that of the non-treated group (27.8 fmoles/mg/proteins) and was significantly lower than that of normal rabbits (58.2 fmoles/mg, p < 0.01). The improvement of ventricular response to catecholamines appears to be due to a myocardial protection by propranolol against the toxic effect of catecholamines in heart failure and not, at least in this model, to an up-regulation of beta-adrenoceptors.