Here is what I have learned. I have not learned anything about the drug specifically in school, but I will explain my thinking. Beta-blockers vasodialate. They are antagonist and usually specific for beta 1 receptors in vascular smooth muscles. When a beta 1 receptor is blocked, catecholamines (adrenaline, norepi) cannot exert there effects on smooth muscle (they cause constriction). Beta 2 receptors are commonly found in the lung on bronchial smooth muscle and are affected in an opposite mannor. Epinephrine and other catecholamines cause smooth muscle relaxation and therefore bronchodialation. Here is where I make the inference. B-Blockers end in -olol such as metoprolol and atenolol. Beta-agonists ,which stimulate beta-receptors, end in -buterol such as albuterol and, well, clenbuterol. Beta-blockers vasodialate and can bronchoconstrict. Beta-agonists would then vasoconstrict and bronchodialate. Let me know if you guys understand it the same way. Interested in other opinions.