Correct option is A
The correct answer is (a).
Norepinephrine. Norepinephrine primarily acts to dilate the airways by stimulating beta-2 adrenergic receptors, which leads to bronchodilation, thereby reducing airway resistance. In contrast, Thromboxane A₂, Histamine, and Leukotriene B₄ are all bronchoconstrictors, meaning they increase airway resistance.
Incorrect options-
Thromboxane A₂ (Option b) causes bronchoconstriction and promotes platelet aggregation, increasing airway resistance and inflammation.
Histamine (Option c) is released from mast cells during allergic responses, causing airway smooth muscle contraction, edema, and mucus secretion, increasing airway resistance.
Leukotriene B₄ (Option d) is a pro-inflammatory mediator that causes bronchoconstriction and recruits immune cells, thus increasing airway resistance in conditions like asthma.
