Pretreatment with ondansetron blunts plasma vasopressin increases associated with morphine administration in ferrets

Postoperative nausea and vomiting are significant problems. A method for measuring vomiting thresholds for anesthetics using plasma markers, such as arginine vasopressin (AVP), would be useful. We measured the change in AVP concentrations associated with morphine alone or in combination with ondansetron pretreatment. Data were collected from ferrets implanted with IV catheters. After recovery, the ferrets were administered IV morphine alone or with ondansetron pretreatment. Baseline blood samples were taken before morphine injection, and at 5, 10, 15, 30, 45, 60, and 90 min after morphine injection. Plasma AVP levels were measured using radioimmunoassay. Morphine alone was associated with a significant increase in plasma AVP concentrations from baseline at 45, 60, and 90 min (P < 0.05). Ondansetron alone did not change the plasma AVP concentration after 20 min (P > 0.46). There was no significant increase (P > 0.46) in AVP concentration in animals that were pretreated with ondansetron before administration of morphine. Two-way analysis of variance confirmed that ondansetron significantly decreased the increase in AVP by morphine at 60 and 90 min (P < 0.05). These data suggest that plasma AVP concentration may be an accurate marker for nausea, and may be useful to guide treatment for this condition.

The antiemetic, ondansetron, has an effect not only on clinically perceived vomiting, but also on plasma vasopressin level.