Effect of Systemic Estradiol Administration on Circadian Body Temperature and Activity Rhythms in Female Rats

Abstract

The estrus cycle affects the circadian body temperature (T b ) and activity rhythms, and progesterone is related to these alterations. However, it is not clear whether estrogen (E 2 ) influences it. The present study examined whether E 2 affects the circadian T b and activity rhythm. Ovariectomized rats were implanted with a silastic plate with or without E 2 underneath the dorsal skin (E 2 (-) and E 2 (+)), and these along with sham operated rats (SH) were measured for T b and activity for 2 weeks. The mean T b was lower, and mean activity was higher in E 2 (+) than that in E 2 (-) in the day. In the dark phase, the slope of the relationship between the mean T b and activity in E 2 (-) was the greatest. The slope in E 2 (+) and SH was greater in the light phase than that in the dark phase. The daily peak of T b and activity was lower in E 2 (+) than that in E 2 (-). The appearance of the nadir in T b was later in E 2 (+) and SH than that in E 2 (-). The appearance of the peak in T b and activity was earlier in E 2 (+) and SH than that in E 2 (-). Thus, E 2 may modulate the circadian T b and activity rhythm in female rats.