Haemodynamic and coronary vascular responses after beta-adrenoceptor blockade in the anaesthetised dog: a comparison of tolamolol with practolol and propranolol

In anaesthetised dogs, the β-adrenoceptor blocking agent tolamolol had approximately ten times the activity of practolol and twice that of propranolol in antagonising the myocardial responses to injected isoprenaline, adrenaline and noradrenaline and to stimulation of the left stellate ganglion. Tolamolol, like practocol was cardioselective amounts which blocked myocardial responses to exogenous catecholamines andtto sympathetic stimulation, it did not block peripheal vasodilatition caused ay isoprenaline, and isoprenaline and adrenaline continued to cause coronary vasodilatation. In contrast, propranolol blocked myocardial, peripheral vascular and coronary vascular responses to isoprenaline to similar degrees. These results imply that the coronary vascular β-adrenoceptors resemble those of the peripheral vasculature. The coronary dilatation due to noradrenaline and stellate ganglion stimulation was generally abolished afterβ-adrenoceptor blockade and in some experiments was converted to a vasoconstriction. β-Adrenoceptor blockade did not affect peak reactive hyperaemia following coronary artery occlusion.