β2-AGONISTS

Summary

The β2-agonists are the most offective bronchodilators  available .  β2-Adrenergic receptor stimulation activates adenyl cuclase,which produces an increase in intraccllular cyclic AMP. This in turn decreases unbound intracellular calcium , producings smooth muscle relaxation.Mast-cell membrane stabilization, and skeletal muscle stimulation.β2 Adrenergic stimulation also activatcs Na’    K’ ATPasc, produces gluconeogenesis , and enhances insulin secretion, producing a mild to moderate decrease in serum potassium concentration.

The Table compares the various β-adrenergic agonists in terms of selectivity.Potency, oral activity , and duration of action.The β2-agonists are functional or physiologic antagonists in that they relax airway smooth muscle regardless of the mechanism for constriction.When administered in equipotent doses , all the short-acting drugs will produce the same intensity of response , the only differences will be in duration of action and cardiac toxicity . All of the β -agonists are more bronchoselective when administered by the aerosol route , Differences in myocardial effect are discernible between selective and nonslective agents even when administered as aerosols . particularly at the higher doses used for acute severe asthma.

  a) Relative molar potency : β 1 most patent.

b)     b) Protection refers to the duration of time that bronchocoustriction may be prevented