[Effects of tetramethylpyrazine on rabbit basilar artery ring and canine vertebroarterial circulation]

Tetramethylpyrazine (TMP) inhibited the contraction of rabbit basilar artery and mesenteric arteries caused by KCl with an IC50 of 1.3 mmol.L-1 and 7.5 mmol.L-1 (P < 0.01). The contraction of the rabbit basilar and mesenteric artery ring evoked by KCl, CaCl2 and norepinephrine was inhibited noncompetitively by TMP with the pD2' values of 2.18 +/- 0.16 and 1.83 +/- 0.18 (P < 0.01), 2.13 +/- 0.12 and 2.08 +/- 0.12 (P > 0.05), 3.08 +/- 0.16 and 2.57 +/- 0.08 (P < 0.01), respectively. The contraction of rabbit basilar artery and saphenous veins evoked by 5-HT was also inhibited by TMP with an IC50 of 0.22 mmol.L-1 and 2.2 mmol.L-1 (P < 0.01), respectively. TMP antagonized the myogenic activity of rat portal vein strips. TMP increased canine vertebroarterial blood flow and had no effect on femoral artery blood pressure. The results suggested that TMP may block the calcium channel, inhibit the contraction of rabbit basilar artery, and improve the canine vertebroarterial circulation selectively.