Trihexyphenidyl (hydrochloride)

Trihexyphenidyl hydrochloride is a selective and orally active M₁ muscarinic receptor antagonist with an IC₅₀ of 3.7 nM for rat cerebral cortex M1 muscarinic receptors. Trihexyphenidyl hydrochloride modulates cholinergic activity, countering acetylcholine supersensitivity in neural pathways. Trihexyphenidyl hydrochloride improves movement disorder, inhibits McN-A-343 (HY-107648)-induced pressor responses, vagally-induced bradycardia and vasodilatation. Trihexyphenidyl hydrochloride can be used for the research of Parkinson's disease.^[1][2][3]. In Vitro:Trihexyphenidyl (45 min) hydrochloride binds with highest affinity to rat cerebral cortex M₁ muscarinic receptors (IC₅₀ = 3.7 nM), moderate affinity to rat submandibular gland receptors (IC₅₀ = 17 nM), and lowest affinity to rat heart receptors (IC₅₀ = 31 nM), with a selectivity ratio of 8 for heart versus cortex receptors^[2]. In Vivo:Trihexyphenidyl (i.v.) hydrochloride shows moderate selectivity for M₁ muscarinic receptor-mediated ganglionic pressor responses over peripheral muscarinic receptor-mediated vagal bradycardia in pithed rats, with a selectivity ratio of 6^[2].
Trihexyphenidyl (i.v.) hydrochloride shows moderate selectivity for M₁ muscarinic receptor-mediated ganglionic nictitating membrane contractions over peripheral muscarinic receptor-mediated vagal bradycardia and vasodilatation in anaesthetized cats, with a selectivity ratio of 9^[2].