Mechanism of the hypotensive effect of tetramethylpyrazine, an amide alkaloid from the stem of Jatropha podagrica

Abstract The mechanism of the hypotensive effect of an amide alkaloid, tetramethylpyrazine (TMPZ), obtained from the stem of JATROPHA PODAGRICA HOOK (Euphorbiaceae) has been investigated in some isolated vascular and extra-vascular smooth muscle preparations. The results obtained show that the amide alkaloid inhibits the contractions of the rabbit isolated perfused central ear artery induced by periarterial electrical stimulation or intraluminally administered noradrenaline; reduces, like papaverine, the amplitude of the spontaneous myogenic contractions, and noradrenaline-evoked contractions of the rat isolated portal vein; inhibits the electrical stimulation-induced or noradrenaline-evoked contractions of the guinea-pig isolated vas deferens and reduces the periarterial electrical stimulation-induced or noradrenaline-evoked relaxations of the rabbit isolated duodenum. The antagonism produced by the amide alkaloid on the responses of these isolated tissue preparations to electrical stimulation or exogenously-added noradrenaline was similar to that elicited by phentolamine, an alpha-adrenoceptor antagonist. It is concluded that tetramethylpyrazine (TMPZ) probably causes hypotension in experimental animals by (a) dilating blood vessels, and/or (b) acting as a non-specific spasmolytic agent (like papaverine).