UCP1 and TRPM8 Expression in the Brown Fat Did Not Affect the Restriction of Menthol-Induced Hyperthermia by Estradiol in Ovariectomized Rats

Abstract

Estradiol (E₂) modulates the central and peripheral thermoregulatory responses to cold. Menthol is an agonist of transient receptor potential melastatin type 8 (TRPM8), which is a peripheral cold receptor. E₂ suppresses menthol-induced elevation of body temperature (T_b) in ovariectomized rats, but the mechanism is unknown. The aim of the present study is to investigate the effect of E₂ on uncoupling protein 1 (UCP1), a thermogenic gene, and TRPM8 mRNA levels in ovariectomized rats applied menthol. A silastic tube was implanted in ovariectomized rats with and without E₂ underneath the dorsal skin (E₂(+) and E₂(−) groups), and data loggers for T_b measurement into peritoneal cavity. After application of 10% L-menthol or vehicle to the skin of the whole trunk of rats, T_b was measured for 2 h. The interscapular brown adipose tissue (BAT) and spinal ganglia of cervical, thoracic, and lumbar parts were obtained for RT-qPCR assay. In the menthol application, T_b in the E₂(+) group was lower than that in the E₂(−) group. The UCP1 mRNA in the BAT, TRPM8 mRNA in the BAT and spinal ganglia in all areas did not differ between the E₂(+) and E₂(−) groups. In conclusion, the UCP1 and TRPM8 expression in the brown fat did not affect the restriction of the menthol-induced hyperthermia by estradiol in ovariectomized rats.