The effects of menstrual cycle on sympathetic skin response and strength–duration properties

Background: Sympathetic control of the circulation is considerably affected by female reproductive hormones. Sudomotor function can be easily evaluated with sympathetic skin response (SSR). Although studies reveal that SSR amplitude decreases with hormone replacement therapy, the effect of estrogen on SSR is unclear. Measuring axonal excitability provides information about the physiological and physical properties of axonal ion channels and nerves. Axonal excitability tests may also give valuable information about the pathophysiology underlying neuronal disorders. In this study, we investigate the influence of female hormones, especially estrogen, on neuronal excitability and the sympathetic nervous system. Methods: SSR and strength–duration time constant (SDTC) tests were conducted on healthy women with a mean age of 26 ± 4 years with regular menstrual cycles. The tests were performed during the first 3 days of the menstrual cycle when the level of estrogen is at its lowest and 2 days before ovulation when the estrogen is at its highest level. Results: SDTC, rheobase, and the latency of SSR were found to be relatively shorter at 2 days before ovulation when compared with the values of the first 3 days of the menstrual cycle. However, the difference was not statistically significant (P > 0.05). Discussion: The SDTC and SSR values in the 2 days before ovulation and the first 3 days of the menstrual cycle did not show any significant differences. We suggested that these parameters do not affect neuronal excitability associated with varied estrogen levels. Conclusion: Further research will be required to fully understand the influence of sex hormones on the nervous system in menstrual cycles, which can suggest underlying mechanisms of various diseases that are linked with autonomic and hormonal alterations.