An Improved Method for Recording Tail Skin Temperature in the Rat Reveals Changes During the Estrous Cycle and Effects of Ovarian Steroids

In the rat, tail skin vasomotion is a primary heat loss mechanism that can be monitored by changes in tail skin temperature (T-SKIN). Previous studies showed that ovariectomy and estrogen replacement modify T-SKIN in the rat. Based on these findings, the ovariectomized (OVX) rat has been used as a model to study the mechanisms and treatment of menopausal hot flushes. It is not known, however, if T-SKIN changes across the estrous cycle in intact rats. Here, we describe an improved method for monitoring T-SKIN in freely moving rats using a SubCue Mini datalogger mounted on the ventral surface of the tail. This method is noninvasive, cost-effective, and does not require restraints or tethering. We observed a distinct pattern of T-SKIN across the estrous cycle characterized by low T-SKIN on proestrous night. To determine whether this pattern was secondary to secretion of ovarian steroids, we monitored the thermoregulatory effects of 17 beta-estradiol (E-2) and E-2 plus progesterone, administered via SILASTIC capsules to OVX rats. E-2 treatment of OVX rats significantly reduced T-SKIN in the dark phase from 2 to 21 d after hormone treatment. The T-SKIN of E-2-treated OVX animals was not significantly different from OVX rats receiving E-2 plus progesterone. These data provide evidence that the reduction in T-SKIN on proestrous night was secondary to elevated levels of ovarian estrogens. This study provides the first description of T-SKIN changes with the estrous cycle and supports the role of estrogens in normal thermoregulation in the rat. (Endocrinology 151: 5389-5394, 2010)