At ambient temperatures of 4°C and 22°C, the average
Tcore of high-estrogen rats was higher than that of low-estrogen
rats (Figure 4). The average oxygen consumption of the
high-estrogen rats was higher than that of the low-estrogen rats.
Progesterone administration increased oxygen consumption in
high estrogen rats, whereas progesterone administration
decreased oxygen consumption in low estrogen rats (Figure 4).
Although differences in motor activities between different
stages in the estrous cycle have been thought to be the reason
for the differences in body temperature in female rats, the high estrogen rats in the present study did
not move more than the low estrogen rats. Therefore the greater oxygen consumption in the
high-estrogen rats was not due increased motor activity. Progesterone has an effect of raising body
temperature, but the effect appears only under the condition of high estrogen concentration. The high
body temperature may not be due to an increase in heat
dissipation at least at Ta above 22°C.