The involvement of brain serotonin systems in the pathophysiology of eating disorders has been repeatedly demonstrated in recent studies. Platelet MAO activity is an index of brain serotonin activity and lowered platelet MAO levels have been found in association with impulsive behaviors. In addition, some preliminary reports indicate that platelet MAO could be lowered in eating disorder patients. Methods: 47 patients with DSM-IV eating disorders were studied, including 30 with bulimia nervosa and 17 with anorexia nervosa binge eating–purging type. Platelet MAO activity was measured by isotopic methods using C-14 benzylamine and compared with a control group of 30 healthy subjects. Impulsive personality features were studied with specific rating scales. Results: Platelet MAO activity was significantly lower (4.4±2.4 nmol/h/108 platelets) in the bulimic patients than in the control group (6.9±2.5) (p<0.001). No significant differences were found between pure bulimics and binge eating–purging anorectics. Platelet MAO was inversely and significantly correlated with scores on impulsivity scales and with borderline personality disorder characteristics. Conclusions: Platelet MAO activity is lowered in patients with bulimia, which may reflect dysfunction in impulse control mechanisms. Since platelet MAO has a predominant genetic component, there is need for studies on the association of low platelet MAO and higher risk for developing eating disorders.
Despite considerable evidence suggesting a link between serotonin (5-HT) function and eating disorders, studies on the functional activity of serotonin are inconclusive. Studies on 5-HT transmission in anorexia nervosa have yielded contradictory results. While some reports have found increased levels of plasma 5-HT and of spinal 5-HIAA in anorectic patients (Kaye et al., 1991), reports on lowered 5-HT function in anorexia nervosa are also described (Hassanyeh and Marshall, 1991). In this sense blunted prolactin concentrations after m-cpp and tryptophan administration have been found Brewerton et al., 1990 and Monteleone et al., 1998 suggesting a decreased serotonin receptor sensitivity in anorexia nervosa.
Most studies have described decreased 5-HT function in patients with bulimia nervosa (Smith et al., 1999). Baseline concentrations of prolactin are lowered in bulimic patients and the response of prolactin has been consistently described as blunted after administration of tryptophan, m-cpp, and fenfluramine ( Brewerton et al., 1992, Goldbloom et al., 1996, Kaye et al., 1998 and Monteleone et al., 1998)
Platelet monoamine oxidase activity (MAO) has been proposed as an index of cerebral 5-HT activity (Oreland and Shaskan, 1983) and has been studied in relation with various psychiatric disorders. Lowered platelet MAO has been repeatedly found in patients with impulsive features, including violent offenders Alm et al., 1994 and Castrogiovanni et al., 1994, impulsive drug users (Von Knorring and Oreland, 1985), pathological gamblers (Moreno et al., 1991 and Carrasco et al., 1994) and borderline personality disorder (Verkes et al., 1996). Preliminary reports indicate that impulsive bulimia could be associated with lowered platelet MAO (Hallman et al., 1990 and Verkes et al., 1996). Low platelet MAO in bulimic patients has been interpreted as a confirmation of decreased 5-HT turnover in these patients. However, the above mentioned studies are inconclusive, due to the small samples of patients and the lack of uniformity of diagnostic criteria of anorexia and bulimia used in the different studies (Biederman et al., 1984).
To confirm these results, a study of platelet MAO activity was designed in a sample of 47 patients with impulsive bulimia, strictly delimited according to DSM-IV diagnostic criteria and including those with bulimia nervosa and those with bulimia associated to anorexia nervosa.
A significantly decreased platelet MAO activity was found in the whole sample of bulimic patients compared with healthy controls. Decreased MAO activity correlates with bulimic symptoms and with impulsive features. Although preliminary, these results suggest a possible role for platelet MAO as a risk factor in the development of clinically significant eating disorders in young adolescents with initial anorectic and bulimic habits. However, the predictive significance of platelet MAO in eating disorders needs further studies with larger samples.
