Dopaminergic abnormalities in bulimia nervosa have been reported in some studies, but results are not consistent across studies. In the present study, clinical characteristics, plasma level of homovanillic acid (pHVA) and two scales – the Eating Attitudes Test (EAT) and the Beck Depression Inventory (BDI) – were assessed in 36 adolescent bulimia nervosa patients (mean age16.3 years, S.D. 1.1) who were consecutively seen on an Eating Disorder Unit. Levels of pHVA were also measured in 16 healthy control adolescents from the general population. Patients had significantly higher mean pHVA than controls. Eighteen patients (50%) had a pHVA level equal to or higher than the mean of control subjects plus one standard deviation, and this group of patients had significantly higher mean BDI scores and non-significantly higher mean EAT scores, although they did not differ from the other patients in age, time elapsed since the onset of disorder, body mass index and number of binges or vomits. Moreover, in logistic regression analysis the BDI score proved to be an independent predictor of high pHVA. The level of pHVA is increased in bulimia nervosa patients with high scores on measures of depressive and eating symptomatology.
Bulimia nervosa is an eating disorder characterized by bingeing and purging. Onset is usually during adolescence, and the condition is associated with severe physical morbidity and psychosocial disability. Its origin is still unclear (Schmidt, 2003), but studies suggest that alterations in the activity of monoamine neurotransmitters, such as serotonin or dopamine, may contribute to some of the disturbances found in bulimia nervosa (Brambilla, 2001). As far as dopaminergic activity is concerned, animal studies have shown rats release dopamine in response to palatable food (Bassareo and Di Chiara, 1999) and when bingeing on sugar (Rada et al., 2005 and Avena et al., 2006). In humans, dopamine has also been associated with eating; higher food intake restraint was associated with greater dopaminergic responsivity to food stimuli (Volkow et al., 2003), and increases in extracellular dopamine in the dorsal striatum were significantly correlated with increases in self-reports of hunger and desire for food (Volkow et al., 2002). In bulimic patients, the results of different studies are inconsistent. In adult patients, some authors have found lower (Jimerson et al., 1992) or normal (Kaye et al., 1990) levels of the dopamine metabolite homovanillic acid (HVA) in cerebrospinal fluid. Brambilla et al. (2001) found similar growth hormone responses to apomorphine stimulation in seven bulimic patients and controls, suggesting that dopaminergic activity is normal in these patients. Nevertheless, other studies have found higher plasma HVA in bulimic and anorexic patients, as well as in psychotic patients, in comparison with other psychiatric disorders such as adjustment disorder (Bowers et al., 1988 and Bowers et al., 1994). These results indicate that there may be an optimal level of dopaminergic activity that mediates normal eating; the differences from study to study may be due to the heterogeneity of the patients included (e.g., different stages of the disorder at which data are collected, age, or duration of disorder).
Homovanillic acid is the main metabolite of dopamine. Levels of homovanillic acid in plasma have been considered a measure of central dopaminergic activity and have been widely used to study the function of central dopamine in psychiatric disorders (Friedhoff and Amin, 1997 and Coccaro et al., 2007). Dopamine neurons (almost all from the central nervous system) contribute to produce plasma homovanillic acid (pHVA). It is estimated that 30% of pHVA originates from dopamine neurons (Amin et al., 1995). Despite this low percentage, pHVA levels have been found to correlate to clinical findings (Stern et al., 1997), and some studies have shown that pHVA levels predict the severity of symptoms (Breier et al., 1993 and Zhang et al., 2001) and response to antipsychotic treatment (Chang et al., 1990 and Yoshimura et al., 2003) in psychotic patients, and point to a relationship between pHVA and central processes.
To our knowledge, no studies have assessed pHVA levels in adolescent patients with bulimia nervosa. As the presence of dopaminergic abnormalities in bulimic patients has not been definitively established, the main objective of the present study was to compare pHVA levels in adolescents with bulimia nervosa and adolescent controls, and to determine if active bulimic patients, or at least a subgroup of them, have higher pHVA concentrations.
