Neuromuscular blocking activity of methanolic extract of Piper sarmentosum leaves in the rat phrenic nerve-hemidiaphragm preparation.

Methanolic extract of Piper sarmentosum Roxb. (Piperaceae) leaves was studied for the neuromuscular blocking activity in rat phrenic nerve-hemidiaphragm preparations. The plant extract, at concentrations of 3.2, 4.0, 4.8 and 6.4 mg/ml, exhibited an initially transient increase in twitch tension which was followed by a marked dose-related neurally-evoked twitch depression. The neuromuscular blocking effect produced by the plant extract was compared with d-tubocurarine (dTC) and succinylcholine (SCh). The EC50 for neurally-evoked twitch depression of the extract, dTC and SCh was 4.07 mg/ml, 1.1 microM and 15 microM, respectively. The neurally-evoked twitch depression produced by the extract was partially antagonized by tetraethylammonium (TEA) but not by neostigmine (NS). These findings suggested that the plant extract possessed a marked neuromuscular blocking activity at the neuromuscular junction and a possible mechanism which was likely to inhibit neurotransmitter (acetylcholine) release at the presynaptic terminal.