Effects of a second heating on rat liver blood flow

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Abstract
Effects of a second heating on blood flow in the liver and cardiac output were studied in Fischer rats. Heating was done by an experimental capacitive heating device using 8 MHz radiofrequency. Thermometry was performed at seven points around the liver with thermocouples. Blood flow and cardiac output were measured with the radioactive microsphere method. The liver was preheated for 30 min at 41 or 43°C, and then reheated 1–7 days later at 41 °C for 15 min. Hepatic arterial blood flow, portal venous blood flow and the cardiac output were measured immediately before and at the end of the reheating. Heating the liver at 41°C for 15 min without preheating slightly increased the hepatic arterial blood flow, and reheating 1–7 days after the first heating caused a greater increase in the hepatic arterial blood flow. Increase in hepatic arterial blood flow caused by reheatings pointed to the development of thermotolerance or thermal adaptation in the hepatic artery. When the liver was heated at 41°C for 15 min without preheating, the portal venous blood flow remained almost unchanged 1–7 days after the heating. On the other hand, a reheating at 41°C for 15 min applied 1–7 days after the preheating reduced the portal venous blood flow. Reduction in portal venous blood flow was approximately parallel to reduction in cardiac output by reheating, pointing to the existence of a casual relationship. Reduction in portal venous blood flow by reheating may also be, in part, due to the decrease in the splanchnic blood flow resulting from a systemic adaptation to the heat stress.