The Effects of Ultrasound Stimulation on Muscle Blood Flow in the Hind Limb and Related Neural Mechanism in Anesthetized Rats

Abstract

The purpose of this study was to investigate the changes in muscle blood flow caused by ultrasound stimulation. Although many studies have been done on the thermal effects of ultrasound therapy and some reports of its effects on muscle blood flow (MBF), the mechanism of the effects on MBF remains to be elucidated. In the present study, using laser Doppler flowmetry, we observed the responses of muscle blood volume (MBV) in the hind-limb evoked by ultrasound stimulation and investigated its neural mechanism in anesthetized rats. The experiments were performed on 7 adult male Wistar rats, which were anesthetized and artificially ventilated. Hind-limbs of the rats were stimulated by continuous wave ultrasound at l or 3 MHz with l or 2 W/cm2 power per 60 seconds. The muscle blood volume was measured with a laser Doppler flow meter using a needle type probe inserted in the bicep femoris. The contribution of sympathetic vasoconstrictor nerves on the responses of MBV evoked by the ultrasound stimulation was investigated with a pharmacological blockade by administrating of a sympathetic alpha blocker (phentramine; 1 mg/kg, iv.). During stimulation at l MHz with 2 W/cm2 power, MBV decreased by a mean of 8% compared with the pre-stimulation control level and the change was statistically significant (p<0.05). After the termination of the stimulation, the lowered MBV response recovered to its control level or even increased in some cases. Pre-administration of sympathetic α-blocker abolished the lowered response in MBV.