Clinical Endocrinology (1998) 48, 761–768 761  1998 Blackwell Science Ltd Diurnal variation of the serum leptin concentration in patients with anorexia nervosa R. K. Støving*, J. Vinten†, A. Handberg†, E. N. Ebbesen*, J. Hangaard*, M. Hansen-Nord*, J. Kristiansen* and C. Hagen* *Department of Endocrinology and Centre for Anorexia Nervosa, Odense University Hospital, Odense and †Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen, Denmark (Accepted 22 July 1997; returned for revision 29 August 1997; finally revised 27 October 1997; accepted 19 November 1997) Summary OBJECTIVE In rodents, leptin is involved in regulat- ing eating behaviour, fat storage, and reproductive function. In humans, the serum leptin concentration in obese and normal weight subjects correlates with body mass index, reflecting the body fat store. The serum leptin exhibit diurnal variation, however, this has been reported to be absent in normal weighted amenorrheic athletes. Anorexia nervosa is associated with multiple endocrine abnormalities. Hypothalamic amenorrhoea often precedes the weight loss and may persist after weight recovery. We hypothesized that leptin could be involved in the regulation of eating behaviour and gonadal function in anorexia nervosa. DESIGN We measured the concentration of leptin in serum samples taken after an overnight fast in 18 female anorexia nervosa patients and 11 controls. To study diurnal variation, eight patients and 11 con- trols were hospitalized for 24 h and had a standardized diet at regular times. Seven blood samples were obtained at 4 h intervals from each subject. PATIENTS The patients fulfilled the DSM-IV criteria for anorexia nervosa. The mean body mass index for the patients was 14·2  2·3 kg/m 2 and for controls 20·3  1·7 kg/m 2 . RESULTS The mean fasting leptin concentration as well as the 24 h mean concentration were significantly lower in the anorectic group than in the control group (2·5  0·9 vs 10·1  6·1 mg/l, P < 0·01 and 2·7  1·5 vs 10·6  7·1 mg/l, P < 0·01 respectively). In the whole group of subjects (n ¼ 28) a significant positive cor- relation between the leptin level and body mass index was found (r ¼ 0·63, P < 0·001). In the anorectic group it was found that the leptin level correlated better with body fat percentage than with body mass index. In normalized data the time course of the mean leptin levels showed a monophasic variation with nadir and zenith at about 0900 and 0100 h respectively. How- ever, the individual coefficients of variance were sig- nificantly lower in the anorectic group compared to the group of healthy women. CONCLUSION In patients with anorexia nervosa the leptin level is low, reflecting the low body fat mass, and the relative diurnal variation is strikingly reduced. The similarity to that of normal weighted women with hypothalamic amenorrhoea suggest that altered leptin oscillations may be of particular significance in the hypothalamic regulation of reproductive function. Leptin, the product of the obese gene (ob), is secreted solely by adipocytes (Lo ¨nnqvist et al., 1995), and its receptor is expressed in the hypothalamus (Lo ¨nnqvist et al., 1995) where it is supposed to act on the satiety mechanism (Campfield et al., 1995). Mutation of the ob gene in mice results in massive hereditary obesity. Administration of recombinant leptin to ob/ ob mice leads to drastic weight reduction due to diminished food intake and increased energy expenditure (Halaas et al., 1995; Pelleymounter et al., 1995). Although a higher dose was required, it is noteworthy that recombinant leptin is also reported to suppress food intake in diet-induced obesity (Campfield et al., 1995), and in normal weight animals (Stephens et al., 1995; Schwartz et al., 1996). Recent evidence suggests that this ‘satiety hormone’ is also implicated in the hypothalamic–pituitary–gonadal function. The ob/ob mice are always sterile with absent oestrus cycles. Thinning of the mice to normal weight did not correct their sterility, but repeated administration of recombinant leptin led to ovulation and pregnancy (Chehab et al., 1996). In humans, the functional role of leptin has yet to be demonstrated. In obese and normal weight subjects, it has been shown that the expression of leptin mRNA and the serum leptin concentration correlated with body fat mass (Maffei et al., 1995; Considine et al., 1996), and the serum leptin concentra- tion exhibited diurnal variation with the highest level between Correspondence: Dr. Rene ´ Klinkby Støving, Department of Endocrinology and Centre for Anorexia Nervosa, Odense University Hospital, 5000 Odense C, Denmark. Fax: þ45 6591 9653. A preliminary report of these results appeared in Diabetologia (1996) 39, A 550 (abstract).