Cholinergic Blocking Effect of Quercetin

Abstract

Quercetin extracted from natural sources such as the leaves of Psidium guajava (Myrtaceae), possessed the cholinergic blocking effect. A pharmacological study of quercetin was made in both rat sciatic nerve-gastrocnemius in in vivo preparation and rat phrenic nerve-hemidiaphragm prepamtion; in in vitro system. From this study it was found that quercetin caused a decrease in neurally-evoked twitch. Quercetin in high dose produced a complete neuromuscular blockade. It was therefore suggested that quercetin produced a synergistic effect on succinyl cholinergic neuromuscular blocking action. However, tetraethylammonium (TEA), neostigmine and Ca²⁺ could not antagonize the neuromuscular blocking effect of quercetin. Further investigation dealing with the post-tetanic potentiation (PTP) was not abolished by quercetin. In addition, quercetin does not have a synergistic effect with hemicholinium (HC₃). Quercetin in high dose could suppress the twitch amplitude of ACh contracture in rat denervated gastrocnemius preparation. Therefore, the results suggested that quercetin exerts its effect on the neuromuscular junction due to depolarized blocking action at the postsynaptic site and/or a decrease sensitivity of motor endplate to ACh. Therefore, the results suggested that quercetin exerts its cholinergic properties at nicotinic site of neuromuscular junction.