Participation of Calcitonin Gene Related Peptide Released via Axon Reflex in the Local Increase in Muscle Blood Flow following Manual Acupuncture

Abstract

Objective The purpose of this study was to determine how calcitonin gene related peptide (CGRP) via axon reflex participates in increasing local muscle blood flow (MBF) following manual acupuncture (MA). Methods Male Sprague–Dawley rats (N=56, 270–350 g) were used. We examined (1) the effects of MA on MBF in the tibialis anterior (TA) muscle in normal rats; (2) the effects of MA on MBF in the TA injected with saline or hCGRP8-37 (low: 2×10−4 mol/litre; high: 2×10−3 mol/litre), a competitive CGRP receptor antagonist, in rats; and (3) the effects of MA on MBF in the TA in capsaicin-treated rats. The capsaicin-treated rats were injected with capsaicin dissolved in an ethanol solution within 24 h after birth (50 mg/kg subcutaneously). MA was applied to the right TA for 1 min. 51Cr-labelled microspheres (15 μm in diameter) were used to measure MBF. Results MA significantly increased MBF without changing arterial blood pressure in normal rats (p<0.05). MA also significantly increased MBF in saline-injected, low hCGRP8-37-injected and high hCGRP8-37-injected rats (p<0.001, 005 and 0.05, respectively). The increases in low and high hCGRP8-37-injected rats were lower than those in saline-injected rats, but the difference was not significant. However, MA did not significantly increase MBF in capsaicin-treated rats (p=0.38). Conclusions We obtained conflicting results, suggesting that the participation of CGRP released via axon reflex may be limited to a local increase in MBF following MA.