Blockade of Adrenergic and Cholinergic Transmissions by Tetramethylpyrazine

Abstract

The pharmacological actions of an amide alkaloid, tetramethylpyrazine (TMPZ), isolated from the stem of Jatropha podagrica HOOK (Euphorbiaceae) have been investigated on the electrically-evoked contractions, relaxations and twitches of some cholinergically- and adrenergically-innervated muscle preparations in vitro and in vivo. The amide alkaloid depressed or abolished the electrically-evoked contractions of the chick oesophagus, rabbit duodenum and guinea-pig vas deferens in vitro. Tetramethylpyrazine also inhibited or abolished the indirect electrically-induced twitches of the rat isolated hemidiaphragm, or the contractions of the cat nictitating membrane evoked by pre-ganglionic cervial sympathetic nerve electrical stimulation in vivo. Moreover, TMPZ prevented or reversed the high frequency electrical stimulation-induced relaxations of the rabbit isolated duodenum. These results were taken to imply blocking actions of the amide alkaloid at the cholinergic and adrenergic neuro-effector junctions, the neuro-muscular junction, and at the ganglia (presumably indicating blockade of peripheral cholinergic and adrenergic transmissions).

The inhibitory effects of TMPZ on the electrically-provoked contractions (or relaxations) of the cholinergically-innervated and adrenergically-innervated muscle preparations set up are thought to be possibly linked with the non-specific spasmolytic action of the amide alkaloid, or, probably mediated through its local anaesthetic (membrane-stabilizing) activity; since its inhibitory effects were not modified by any specific antagonist. The pharmacological implications of the above findings are discussed.

Key Word Index

Jatropha podagrica - Euphorbiaceae - Amide Alkaloid Tetramethylpyrazine - Non-Specific Spasmolytic Agent - Blockade of Adrenergic and Cholinergic Transmissions - Blockade of Sympathetic Ganglia - Local Anaesthetic Activity - Hypotensive Action