Acetylcholine does not participate in the increase in local muscle blood flow following manual acupuncture in rats

[Objective] The purpose of this study was to investigate the participation of acetylcholine (ACh) in an increase in muscle blood flow (MBF) by manual acupuncture (MA). [Materials and methods] The experimental animal was the male Sprague-Dawley rat (270-350 g, n = 54). They were pretreated with the muscarinic cholinergic receptor antagonist (atropine; 0.2, 2, and 20 mg/kg IP) or saline as a control. 51 Cr-labelled microspheres were used to measure the MBF in the right hindlimb muscles, including the tibialis anterior (TA), extensor digitorum longus (EDL), soleus (Sol), plantaris (Pla), and gastrocnemius (Gas). MA, by using the sparrow pecking technique, was simultaneously applied to the right TA and EDL for 1 minute. The arterial blood pressure was recorded via a catheter inserted into the right common carotid artery. [Results] MA significantly increased the MBF of both the TA and EDL in both saline-pretreated and atropinepretreated rats. Atropine did not influence the increase in local MBF by MA at either concentration. There were no significant differences in the mean arterial blood pressure (MAP) before, during, or after MA. [Discussion and Conclusion] These findings suggest that ACh are not responsible for the increase in local MBF by MA. The further research is necessary to clarify the mechanism.