Fluoxetine normalizes increased cardiac vagal tone in bulimia nervosa

Patients with bulimia nervosa have been reported to respond to treatment with the serotonin uptake inhibitor fluoxetine. In a preliminary study, which had a small sample size, women with bulimia nervosa were reported to have elevated cardiac vagal tone. We investigated cardiac vagal tone in women with bulimia nervosa before and after treatment with fluoxetine. At baseline, resting cardiac vagal tone, deduced from the respiratory component of heart rate variability, was quantified in 41 healthy volunteer women and in 25 women with bulimia nervosa. The bulimic women received in a parallel-group design, double blind, either placebo or fluoxetine 60 mg/24 hr for 8 weeks. All patients participated in behavioral therapy. Resting cardiac vagal tone was measured again at the end of the treatment. Women with bulimia nervosa had higher cardiac vagal tone than age-matched healthy volunteer women. Placebo had no effect on cardiac vagal tone. Fluoxetine reduced cardiac vagal tone among the women with bulimia nervosa to a level similar to the healthy volunteer women. Women with bulimia nervosa have elevated resting cardiac vagal tone. Fluoxetine normalized the elevated resting cardiac vagal tone among the women with bulimia nervosa. At both the central and peripheral levels, vagal neurons are endowed with serotonin-3 receptors. In vitro, fluoxetine desensitizes or blocks serotonin-3 receptors. A controlled trial of serotonin-3 receptor blockers is warranted in bulimia nervosa.