Effects of estrogen on thermoregulatory tail vasomotion and heat-escape behavior in freely moving female rats

Effects of estrogen on thermoregulatory vasomotion and heat-escape behavior were investigated in ovariectomized female rats supplemented with estrogen (replaced estrogen rats) or control saline (low estrogen rats). First, we measured tail temperature of freely moving rats at ambient temperatures (T- a) between 13 and 31 degreesC. Tail temperature of the low estrogen rats wa s higher than that of the replaced estrogen rats at T-a between 19 and 25 d egreesC, indicating that the low estrogen rats exhibit more skin vasodilati on than the replaced estrogen rats. There was no significant difference in oxygen consumption and core temperature between the two groups. Second, we analyzed heat-escape behaviors in a hot chamber where rats could obtain col d air by moving in and out of a reward area. The low estrogen rats kept Ta at a lower level than did the replaced estrogen rats. These results imply t hat the lack of estrogen facilitates heat dissipation both by skin vasodila tion and by heat-escape behavior. Ovariectomized rats may mimic climacteric hot flushes not only for autonomic skin vasomotor activity but also for th ermoregulatory behavior.