Methacholine bromide (Acetyl-β-methylcholine bromide) is a potent muscarinic-3 (M3) agonist that specifically acts on acetylcholine receptors located on smooth muscle, inducing bronchoconstriction and narrowing of the airways. Its high sensitivity in identifying bronchial hyperresponsiveness (BHR), a hallmark of asthma, makes it useful in the assessment of airway hyperresponsiveness (AHR) as a diagnostic tool for individuals exhibiting asthma-like symptoms with normal resting expiratory flow rates [1] [2] [3] [4].

Methacholine bromide (0.5 μg/kg plus 5 μg/kg/min for 30 min) induces bronchoconstriction in dogs [4]. Methacholine bromide (0.5 mg/kg; i.v.) induces bronchoconstriction was inhibited in a dose-dependent manner by bradykinin (4-40 μg/kg; i.v.) in mouse [5]. Animal Model: 9-week female BALB/c mice [6] Dosage: 0.03, 0.1, 0.3, 1 mg/kg Administration: I.v Result: Induced severe bronchoconstriction.