About terbutalinea alfa2-adrenergic agonist,a fast-acting bronchodilator, tocolytic,anti asthma.mechanism of action of terbutalineterbutaline is a ?2 receptor agonist. terbutaline directly relaxes the airway smooth muscles and produces bronchodilation. stimulation of ?2 receptors activates gs adenylyl-cyclase -cyclic amp path way and produces reduction in smooth muscle tone. ?2 receptor agonists also increases the conductance of large ca2+sensitive k+ channels in airway smooth muscles and leads to membrane hyperpolarisation and relaxation of smooth muscles. tocolytic action: in premature labour terbutaline relaxes uterine smooth muscles and inhibits uterine contractions.