Methoctramine tetrahydrochloride is a potent and cardioselective antagonist of the M2 muscarinic receptor, capable of inhibiting Muscarine-induced bradycardia in vivo.

Methoctramine tetrahydrochloride attenuates Acetylcholine (ACh)- and Arecaidine propargyl ester (APE)-induced increases in PG synthesis in a concentration-dependent manner[1]. Methoctramine (0.01-1 μM) tetrahydrochloride causes facilitation of contractions induced by both pre- and postganglionic nerve stimulation in the guinea-pig isolated, innervated tracheal tube preparation[2]. Methoctramine (≥10 μM) tetrahydrochloride reduces responses to both nerve stimulation and exogenous ACh[2].

Methoctramine (300 μg/kg; i.v.) tetrahydrochloride strongly inhibits the Methacholine- and Muscarine-induced bradycardia in the anaesthetized rat, respectively[3].