Comparison [correction of Compariso] of sympathetic nerve response to head-up tilt in summer [correction of sumer] and winter.

The seasonal adaptation of humans is accomplished metabolically by increased or decreased body heat production and by cardiovascular adjustments which result in decreased or increased heat loss from the body. The sympathetic nervous system plays an important role in thermoregulation and in blood pressure regulation. Muscle sympathetic nerve activity (MSNA) has an essential role in blood pressure regulation in humans. However, it has not yet been clarified how the MSNA changes during seasonal adaptation or how these changes may contribute to long-term thermoregulation in relation to blood pressure regulation. The purpose of the present study was to elucidate if seasonal variations exist in responses of the sympathetic nervous system in humans for gravity-dependent blood pressure regulation.