Changes in the lactate threshold during treadmill exercise after microsphere-induced infarction in rats

The aim of this study was to clarify changes in the lactate threshold (LT) in the acute period after cerebral infarction. Cerebral infarction was induced by the injection of microspheres (MS) into the right internal carotid artery. To estimate the degree of neurologic deficit caused by surgery, the behaviors of all rats were evaluated in terms of typical symptoms of stroke in rats. The rotarod test was used to evaluate equilibrium function. Rats were forced to perform stepwise treadmill exercises, and serial changes in blood lactate concentration were measured for determination of the LT. The average treadmill speed at the LT and the rotarod test performance in MS rats was significantly lower than those in sham-operated rats on postsurgery day 2. However, although neurologic deficits disappeared on postsurgery day 7 in MS rats, LT level and rotarod test performance were significantly lower than in sham-operated rats. These results suggest that the decrease in LT in the acute period after cerebral infarction might be induced by impaired equilibrium function. Other possibilities are discussed as well.