Cinnamaldehyde application decreases tail temperature in ovariectomized rats with and without estradiol administration.

The aim of this study was to examine the effect of estradiol (E₂) on the thermoregulatory responses induced by cinnamaldehyde, a component extracted from cinnamon at 16 °C or 27 °C. The thermoneutral and subneutral experiments were performed to evaluate the augmented effect of cinnamaldehyde by cold exposure and the effect of cinnamaldehyde itself. Ovariectomized rats were implanted with a silastic tube with or without E₂ (E₂(+) and E₂(-) groups), and data loggers into the peritoneal cavity. After the application of 30% cinnamaldehyde or vehicle into the skin of the whole trunk of rats, the rats were exposed to 16 °C or 27 °C for 2 h. Body temperature (T_b) and tail temperature (T_tail) were measured using a data logger and thermography. After exposure, blood samples were obtained, and plasma catecholamine concentration were measured by high-performance liquid chromatography. In the E₂(-) group exposed to 27 °C, the change in T_b in rats applied cinnamaldehyde was significantly lower than that of rats applied vehicle. The change in T_tail in rats applied cinnamaldehyde was significantly lower than that of rats applied vehicle in both E₂(-) and E₂(+) groups at 27 °C and 16 °C. Plasma catecholamine concentration at 27 °C was not different among the groups. E₂ might not affect thermoregulatory responses induced by cinnamaldehyde application; however, it decreased T_tail in female rats.