Vasopressin and oxytocin responses to illusory self-motion and nausea in man

Vasopressin and oxytocin are nonapeptides secreted from the neurohypophysis; increases in vasopressin are associated with nausea and vomiting in some, but not all, species. Our aim was to determine whether plasma vasopressin and oxytocin levels were altered in healthy volunteers who did or did not develop nausea during vection, an optokinetic stimulus which produces the illusion of self-motion. Vection was produced by rotating a drum with an inner surface of black and white vertical stripes around the seated stationary subject. Gastric myoelectrical activity was recorded continuously throughout the experiment with electrodes positioned on the abdominal surface. Plasma samples were obtained before vection and after drum rotation stopped when nausea and tachygastria were present. Vasopressin and oxytocin were extracted from plasma and quantified by RIA. During vection six subjects reported nausea and developed gastric dysrhythmias; six other subjects had no nausea and remained in normal 3-cpm myoelectrical rhythms. Vasopressin and oxytocin values before vection were similar in each group of subjects. One minute after vection stopped, plasma vasopressin levels were significantly greater (P less than 0.05) in subjects experiencing nausea and tachygastrias (35.4 +/- 26.7 pmol/L) than in those without symptoms (2.7 +/- 0.47 pmol/L). Oxytocin levels were unchanged by either vection or nausea. It is concluded that 1) vasopressin, not oxytocin, neurons in the magnocellular-neurohypophyseal system are activated during vection-induced nausea and gastric dysrhythmias; and 2) illusory self-motion may be used safely to study the neuroendocrine responses to brain-gut interactions and nausea in man.