Prenalterol: a partial beta 1-adrenoceptor agonist or a beta-blocker with intrinsic activity?

Hemodynamic studies have demonstrated a significantly reduced beta 1-adrenoceptor stimulating effect of prenalterol compared to dobutamine suggesting a partial agonism on the receptor. In order to prove this hypothesis we administered 80 micrograms/kg of prenalterol within 5 minutes in 8 healthy volunteers during a continuous infusion of dobutamine (15 micrograms/kg/min). In addition to heart rate, blood pressure and the double product, the systolic time intervals QS2I, PEP and LVET and the echocardiographically determined parameters FS and Vcf were measured for evaluation of ventrical function. The injection of prenalterol caused a distinct attenuation of the cardiostimulating effects of dobutamine: there was a prompt fall in heart rate and systolic blood pressure and a typical negative inotropic effect on the parameters of left ventricular function. In the experimental conditions selected, the effects of prenalterol were those of a beta-sympatholoytic agent. Prenalterol should therefore be classified as a partial beta 1-adrenoceptor agonist or as a beta-blocking agent with pronounced intrinsic sympathomimetic activity. The beta 1-stimulating potency of prenalterol amounts to about 60% of a full agonist.