Pharmacological studies on ginger. II. Pressor action of (6)-shogaol in anesthetized rats, or hindquarters, tail and mesenteric vascular beds of rats.

When (6)-shogaol (0.5 mg/kg, i.v.) was administered to rats, blood pressure showed a tri-phasic response which was comprised of a rapid fall, followed by a rise and a delayed fall. The rapid fall, which followed immediately after injection of (6)-shogaol, disappeared with the use of atropine and vagotomy. The marked rise, which occurred after the rapid fall, was not affected by alpha-adrenoceptor blockades, Ca antagonists and ganglion blockade. However, a combination of alpha-adrenoceptor blockade and Ca antagonist inhibited this pressor response. In hindquarters perfused with a nutrient solution, (6)-shogaol (10(-5) g)-induced peripheral pressor response was also not affected by alpha-adrenoceptor blockades and Ca antagonists, but was inhibited by the combination of an alpha-adrenoceptor blockade and a Ca antagonist. Furthermore, this peripheral pressor response was eliminated by the removal of Ca ion from the perfusate. (6)-Shogaol did not exhibit a pressor response in an artery and a vein of the tail or an artery of the femur perfused with a nutrient solution. (6)-Shogaol-induced peripheral pressor response in hindquarters was markedly potentiated during the perfusion of norepinephrine (5 X 10(-6) g/ml), but this potentiation was prevented by pretreatment with reserpine (5 mg/kg, i.p.). Moreover, repeated injections of (6)-shogaol caused a tachyphylaxis in mesenteric and tail vascular beds and a slight tachyphylaxis in hindquarters.