Acute hypotensive effect of combined beta1-adrenoceptor blockade and beta2-adrenoceptor stimulation in spontaneously hypertensive rats (SHR).

The effect on heart rate (HR) and blood pressure (BP) of metoprolol, propranolol and terbutaline, applied alone or in combinations was studied in spontaneously hypertensive rats. Terbutaline had little effect on BP and HR. Propranolol combined with terbutaline had no effect while metoprolol combined with terbutaline decreased BP by 48 mm Hg without affecting HR. Thus the beta2-mediated increase in peripheral vascular resistance after terbutaline was revealed by a drop in BP after beta1-blockade by metoprolol, but not when both beta1-and beta2-receptors were blocked by propranolol.