Changes in blood flow in locally heated intestine of rats

Male Fischer rats were surgically castrated through a lower midline incision and a 5-8 cm long segment of small intestine was fixed to the interior of the right scrotum. Two weeks after the surgery, the herniated intestine was heated by immersing the scrotum into a water bath at different temperatures and the blood flow in the intestine was measured with the radioactive microsphere method. The blood flow in the herniated intestine increased 1.5-2.0 times when the scrotum was heated with 42.5 and 43.5 degrees C water baths for 60-90 min, but began to decrease when heated longer, although the blood flow after heating for 120 min at these temperatures was still slightly larger than the blood flow before heating. Upon heating the scrotum with 44.5 degrees C water bath, the blood flow in the herniated intestine increased to 3-fold of control by 90 min and then rapidly recessed. Massive histological damage was observed 24 h after heating with 44.5 degrees C water bath for 60 min. The blood flow in the intestine measured 1 day after 60 min heating with 43.5 degrees C and 44.5 degrees C water bath was found to be only slightly decreased. Given the relatively small decrease in blood flow, the severe damage in the intestine 24 h after heating may be attributed to direct damage to parenchymal cells.