Bind to β-receptors on cardiac & smooth muscle tissues. They also have important actions in other tissues, especially bronchial smooth muscle (relaxation), the liver (stimulate glycogenolysis) & kidneys (stimulated renin release).
Normally bind to NE released by sympathetic adrenergic nerves, & to circulating epinephrine. Therefore, β-agonists mimic the actions of sympathetic adrenergic stimulation acting through β-adrenoceptors. Overall, the effect of β-agonists is cardiac stimulation (increased HR, contractility, conduction velocity, relaxation) & systemic vasodilation.