Plasma vasopressin, an etiologic factor of motion sickness in rat and human?

Arginine vasopressin (AVP) is considered as an etiologic hormone in motion sickness. However, the possible role of plasma AVP in motion sickness is still controversial. A number of studies have found a gender difference in susceptibility to motion sickness in humans and experimental animals, with female subjects being more susceptible. However, the existence of a gender difference in the AVP response to motion sickness is not known. This study was designed to verify the assumption that plasma vasopressin plays a role in motion sickness. Changes in plasma vasopressin were observed after motion sickness-inducing rotatory stimuli in both sexes in human subjects and rats receiving or not anti-motion-sickness treatments. Plasma vasopressin levels in motion sickness rats exhibited a decrease after rotation in female, but not in male rats. The vasopressin content of the pituitary increased in both sexes. Plasma vasopressin in rats of both sexes tended to increase after a 15-day adaptive training of rotation, but pituitary vasopressin content was not affected under this condition. In contrast, in human subjects, plasma vasopressin levels increased after rotation in all males, but not in females. When anti-motion-sickness drugs (domperidone 10 mg + flunarizine 5 mg) were administered, plasma vasopressin levels were elevated in both females and males. It is concluded that plasma vasopressin increases after motion sickness-induced stimulation provided subjects have become trained to motion sickness. These results do not support an etiologic role of plasma vasopressin in the genesis of motion sickness.