The respiratory symptoms of asthma(哮喘) result from constriction of the bronchi(支气管) and bronchioles(细支气管) of the lungs caused by contraction of the smooth muscle of their walls. This constriction can be reserved by raising the [cAMP] in the smooth muscle. Explain the therapeutic(治疗) effects of albuterol(舒瑞灵,沙丁胺醇), a β-adrenergic agonist taken (by inhalation通过吸入) for asthma. Would you expect this drug to have any side effects? Hoe might one design a better drug that did not have these effects.