Hepatic blood flow responses to mechanical stimulation of the skin in anaesthetised rats

The aim of the present study was to investigate how hepatic blood flow (HBF) changes in response to mechanical stimulation of different areas of the skin in anaesthetised rats, by focusing on involvement of the hepatic sympathetic nerves in and contribution of systemic circulatory changes to the HBF responses. HBF was measured at the surface of the left lateral lobe using the laser Doppler flowmetry. Both innocuous and noxious mechanical stimuli were applied to skin areas of the abdomen and hindlimb. Innocuous mechanical stimulation (brushing) of the abdomen and hindlimb did not significantly change HBF, while noxious mechanical stimulation (pinching) of the abdomen and hindlimb did. The responses to pinching were dependent on the sites stimulated. Pinching of the abdomen decreased, while pinching of the hindlimb increased the HBF. The decrease of HBF in response to abdominal pinching remained after the spinal cord was transected at T1–2 level, but the response was diminished after hepatic sympathetic nerves were severed. On the other hand, the increase of HBF in response to hindlimb pinching was dependent on the increase in blood pressure, and was not influenced by the severance of hepatic sympathetic nerves, and the responses to hindlimb pinching were almost absent after the spinal cord was transected. Based on these results, we suggest that noxious mechanical stimulation of the skin produces changes of HBF, either as a reflex response via activation of the hepatic sympathetic nerves or as a passive response to systemic circulatory changes, depending on the sites stimulated.