Although acupuncture has a significant clinical benefit, the mechanism of acupuncture remains unclear.
Vasopressin, a posterior pituitary
hormone, is involved in
nausea and
vomiting in humans and dogs. To investigate the
antiemetic effects of acupuncture on
vasopressin-induced
emesis, gastroduodenal motor activity and the frequency of retching and
vomiting were simultaneously recorded in conscious dogs. In seven dogs, four force transducers were implanted on the serosal surfaces of the gastric body, antrum, pylorus, and duodenum. Gastroduodenal motility was continuously monitored throughout the experiment.
Vasopressin was intravenously infused at a dose of 0.1 U x kg(-1) x min(-1) for 20 min.
Electroacupuncture (EA, 1-30 Hz) at pericardium-6 (
PC6), bladder-21 (BL21), or stomach-36 (ST36) was performed before, during, and after the
vasopressin infusion. To investigate whether the
opioid pathway is involved in EA-induced
antiemetic effects,
naloxone (a central and peripheral
opioid receptor antagonist) or
naloxone methiodide (a peripheral
opioid receptor antagonist) was administered before, during, and after EA and
vasopressin infusion.
Intravenous infusion of
vasopressin induced retching and
vomiting in all dogs tested. Retrograde peristaltic contractions occurred before the onset of retching and
vomiting. EA (10 Hz) at
PC6 significantly reduced the number of episodes of retching and
vomiting. EA at
PC6 also suppressed retrograde peristaltic contractions. In contrast, EA at BL21 or ST36 had no
antiemetic effects. The
antiemetic effect of EA was abolished by pretreatment with
naloxone but not
naloxone methiodide. It is suggested that the
antiemetic effect of acupuncture is mediated via the central
opioid pathway.