Effects of tetrandrine on hypertensive responses induced by electric stimulation and alpha-adrenoceptor agonists in pithed rats

Tetrandrine (Tet) 5 mg.kg-1 i.v. inhibited the pressor action of norepinephrine (NE) release induced by electric stimulation (10 V, 0.5-16 Hz) of spinal cord T11-L2. However, Tet 5 mg.kg-1 ia did not obviously attenuate the hypertensive responses to NE 0.51-16.91 micrograms.kg-1 i.v., indicating that Tet did not affect the alpha 1-adrenoceptors-mediated vasoconstriction. Tet 5 mg.kg-1 ia decreased the pressor responses to NE 0.05 and 0.17 micrograms.kg-1 i.v. and markedly reduced the dose-dependent hypertensive responses to B-HT920 i.v., a selective alpha 2-adrenoceptor agonist, proving that Tet reduced alpha 2-adrenoceptors-mediated vasoconstriction.