The effect of electro-acupuncture stimulation on the muscle blood flow of the hindlimb in anesthetized rats.

The effect of electro-acupuncture stimulation (EAS) on blood flow in the muscle biceps femoris (MBF) and on mean arterial pressure (MAP) was investigated in anesthetized, artificially ventilated rats. EAS was applied to a hindpaw for 30 s at intensities of 0.1-10.0 mA and at frequencies of 1-20 Hz, and MBF was measured by laser Doppler flowmetry. EAS at less than 1.0 mA, which excited group II fibers maximally and III fibers partially in a saphenous nerve, had no significant effect on MBF or MAP, although both revealed variable responses. EAS at 1.5 mA, which additionally excited group III fibers almost maximally and was subthreshold for group IV fibers, produced a small but significant increase in MBF and MAP. These responses were further increased at 2.0 mA or more, which was suprathreshold for group IV fibers. The increased response of MBF at 10.0 mA was followed by a small decrease in MBF. EAS at 1.5 mA or more also elicited a decrease in renal blood flow (RBF) and an arterial pressor response. Following severance of the bilateral splanchnic nerves, EAS at 10.0 mA induced only a slight increase in MAP and a decrease in MBF. The decrease in MBF was abolished following further severance of the bilateral lumbar sympathetic trunks (LSTs). In conclusion, EAS to a hindpaw at a stimulus strength sufficient to excite group III and IV afferent fibers, particularly group IV afferent fibers, can produce a reflex decrease in MBF via a reflex activation of muscle sympathetic activity, although this decrease in MBF is overridden by an increase in MBF caused passively by a reflex MAP pressor response elicited by a reflex increase, at least in splanchnic sympathetic activity.