Contribution of Sympathetic Nerve Activity to the Thoracic Duct Lymph Flow during Acute Heat Stress

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Effects the acute stress on the regional lymph into the thoracic duct in conscious rats were examined. We found the temperature dependence of the regional lymph into the thoracic duct during heat stress, i.e., the decrease of the regional lymph flow into the thoracic duct followed the increase of the colonic temperatrure. The regional lymph flow into the thoracic duct decrease by 18%, 30% and 40% according to the increase of the colonic temperature in 1゜C, 2゜C and 3゜C, respectively. These findings suggest that the regional lymph flow into the thoracic duct was dependent on the colonic temperature during acute heat stress.To evaluate the causes of the decrease of the lymph flow into the thoracic duct, we measured visceral(renal or mesenteric) blood flow and the hindlimb(the abdominal aorta on the distal side of the renal artery) blood flow as non-viscreal(skin ＆ muscle) blood flow by a pulse Doppler flowmeter. Body temperature was raised by 2゜C with putting the rats into the oven controlled ambient temperature. Regional blood flow of the hindlimb decreased in 33%. The mesenteric or renal blood flow decreased in 34% or 19%, respectively. We calculated the changes of the regional lymph from the visceral and non-visceral organs into the thoracic duct, assuming that the changes of the regional blood flow directly affect the changes of the formation of the regional lymph. The calculated decrease of the lymph flow into the thoracic duct in 21%, which was 70% of the measured decrease of the lymph flow into the thoracic duct(30%). These results suggest that the changes of the regional blood flow during acute heat stress exert the predominant influence on the rate of the regional lymph flow into the thoracic duct in the rat.