orexins - a and -b , which are also called hypocretins , have recently been identified as novel 
 hypothalamic neuropeptides ( 1 ) .
they strongly activate 
 the appetite of animals through action in the lateral hypothalamus , and have been implicated 
 in the central regulation of metabolic rate and glucose homeostasis . on the other hand , 

it inhibits the 
 orexinergic pathway of acceleration of food intake in the lateral hypothalamic area .
both orexin - a and -b are derived from a common precursor preproorexin , which consists of 
 131 amino acid residues , by proteolytic processing ( 2 ) .
orexin - a and -b consist of 33 and 28 amino acids , and their molecular weight are 
 3561 and 2899 , respectively .
there are two types of orexin receptors , both of which are 
 coupled with g - protein .
the affinity of orexin 1 receptor ( ox1r ) is 50 times higher to 
 orexin - a than to orexin - b , while orexin 2 receptor ( ox2r ) shows equal affinity to both types 
 of ligands .
orexinergic neurons are known to project to multiple neuronal systems ( 3 ) , and the physiological role of orexin in the central 
 nervous system ( cns ) has been elucidated at least partly .
the gene expression of orexin is 
 regulated by blood glucose and feeding ( 4 , 5 ) .
moreover , orexin regulates the sleep - wake cycle and 
 other behaviors such as grooming through a dopaminergic pathway in cns .
depletion of orexin 
 in cns plays a central role in the pathogenesis of narcolepsy in both animals and man ( 6 , 7 ) .
the orexin gene is expressed in the testis ( 8) , 
 ovary , intestine ( 9 ) , pancreas ( 10 ) , and adrenals ( 11 ) .
although 
 orexin - a occurs in blood in a substantial amount , little is known about the action mechanism 
 of orexin - a in peripheral tissues .
orexin - a , but not orexin - b , permeates the blood brain 
 barrier ( 12 ) .
orexin - a , when administered 
 intra - peritoneally to the rat , stimulates insulin secretion by direct action on the 
 pancreatic islets ( 10 ) .
we have already demonstrated 
 that orexin - a stimulates catecholamine synthesis in bovine adrenal medullary cells via the 
 ox1r route ( 13 ) . to our knowledge
the 
 present study was designed to determine the plasma level of orexin and its relationship with 
 other metabolic and anthropometric markers in obese children .
forty - seven obese japanese children , consisting of 31 boys and 16 girls , who visited the 
 clinic for obese children at either the university of yamanashi or the university of 
 occupational and environmental health , were consecutively enrolled in the study ( table 1table 1 anthropometric data in control and obese children ) . according to the criteria for obesity in childhood adopted by the ministry 
 of health , labor and welfare in japan ,
a child was considered to be obese when the body 
 weight exceeded 120% of the standard body weight , which is defined as the mean body weight 
 corresponding to the height for that age obtained from the national statistics for 
 japanese school children in 1990 .
the ages of the subjects were 10.4  0.5 ( mean  s.e.m . ) 
 yr , and their percentage overweight was 42.9  1.9% .
blood was drawn after an overnight fast and they were subjected to 
 anthropometric measurements including height , body weight , waist circumference , hip 
 circumference , and triceps and subscapular skinfold thicknesses . the age - matched control group for measuring orexin and leptin ( mean age , 10.4  0.3 yr ) 
 consisted of 26 nonobese children , 13 boys and 13 girls ( table 1 ) .
blood was 
 drawn after an overnight fast . since there were no significant sex - related differences 
 among the anthropometric and clinical laboratory data in either the obese or control 
 children , the boys and girls
the human study committee of the university of yamanashi and the university of 
 occupational and environmental health approved this study .
informed consent was obtained 
 either from each subject or from his or her parents as appropriate .
anthropometric measurements were performed , as described previously ( 14 ) , by the medical staff at both clinics . in brief , 
 height was measured to the nearest 0.1 cm and body weight to the nearest 0.1 kg using a 
 stadiometer .
the waist circumference was measured at the level of the umbilicus , and hip 
 circumference at the level of maximum extension of the buttocks , to the nearest 0.1 cm . 

skinfold thickness was measured to the nearest 0.1 cm using the skinfold calipers at 
 triceps ( halfway between the acromion and the olecranon ) and subscapular ( 1 cm below the 
 inferior angle of the scapula ) .
the percentage overweight was calculated using a small 
 programmed calculator ( pocket growth checker gen-185 , sumitomo pharmaceuticals co. , osaka , 
 japan ) .
the percentage body fat , based on the sum of triceps and subscapular skinfold 
 thicknesses , was obtained using brozek s equation ( 15 ) , after body density was calculated according to nagamine s formula ( 16 ) .
orexin - a in human plasma was assayed by a radioimmunoassay kit ( peninsula laboartory 
 inc . ,
leptin in human plasma was assayed by an enzyme - linked 
 immunosorbent assay kit ( ibl co. , ltd . , fujioka , gunma , japan ) .
clinical blood biochemical data were obtained from the 
 clinical laboratories of both the university hospital of yamanashi and the university 
 hospital of occupational and environmental health .
low - density lipoprotein - cholesterol 
 ( ldl - c ) was calculated using the friedewald equation [ ldl - c = tc  hdl - c 
the statistical analyses were performed using spss version 11.0.1j 
 ( spss japan inc . , tokyo , japan ) .
forty - seven obese japanese children , consisting of 31 boys and 16 girls , who visited the 
 clinic for obese children at either the university of yamanashi or the university of 
 occupational and environmental health , were consecutively enrolled in the study ( table 1table 1 anthropometric data in control and obese children ) . according to the criteria for obesity in childhood adopted by the ministry 
 of health , labor and welfare in japan ,
a child was considered to be obese when the body 
 weight exceeded 120% of the standard body weight , which is defined as the mean body weight 
 corresponding to the height for that age obtained from the national statistics for 
 japanese school children in 1990 .
the ages of the subjects were 10.4  0.5 ( mean  s.e.m . ) 
 yr , and their percentage overweight was 42.9  1.9% .
blood was drawn after an overnight fast and they were subjected to 
 anthropometric measurements including height , body weight , waist circumference , hip 
 circumference , and triceps and subscapular skinfold thicknesses . the age - matched control group for measuring orexin and leptin ( mean age , 10.4  0.3 yr ) 
 consisted of 26 nonobese children , 13 boys and 13 girls ( table 1 ) .
blood was 
 drawn after an overnight fast . since there were no significant sex - related differences 
 among the anthropometric and clinical laboratory data in either the obese or control 
 children , the boys and girls
the human study committee of the university of yamanashi and the university of 
 occupational and environmental health approved this study .
informed consent was obtained 
 either from each subject or from his or her parents as appropriate .
anthropometric measurements were performed , as described previously ( 14 ) , by the medical staff at both clinics . in brief , 
 height was measured to the nearest 0.1 cm and body weight to the nearest 0.1 kg using a 
 stadiometer .
the waist circumference was measured at the level of the umbilicus , and hip 
 circumference at the level of maximum extension of the buttocks , to the nearest 0.1 cm . 

skinfold thickness was measured to the nearest 0.1 cm using the skinfold calipers at 
 triceps ( halfway between the acromion and the olecranon ) and subscapular ( 1 cm below the 
 inferior angle of the scapula ) .
the percentage overweight was calculated using a small 
 programmed calculator ( pocket growth checker gen-185 , sumitomo pharmaceuticals co. , osaka , 
 japan ) .
the percentage body fat , based on the sum of triceps and subscapular skinfold 
 thicknesses , was obtained using brozek s equation ( 15 ) , after body density was calculated according to nagamine s formula ( 16 ) .
orexin - a in human plasma was assayed by a radioimmunoassay kit ( peninsula laboartory 
 inc . , belmont , ca , usa ) .
leptin in human plasma was assayed by an enzyme - linked 
 immunosorbent assay kit ( ibl co. , ltd . , fujioka , gunma , japan ) .
clinical blood biochemical data were obtained from the 
 clinical laboratories of both the university hospital of yamanashi and the university 
 hospital of occupational and environmental health .
low - density lipoprotein - cholesterol 
 ( ldl - c ) was calculated using the friedewald equation [ ldl - c = tc  hdl - c 
the statistical analyses were performed using spss version 11.0.1j 
 ( spss japan inc . , tokyo , japan ) .
table 2table 2 data on clinical blood biochemistry for obese children ( n=47 ) summarizes the data on clinical blood biochemistry for obese children .
plasma 
 orexin - a concentration was higher in obese children ( 17.0  0.4 pg / ml ; p<0.001 ) than in 
 the control children ( 13.5  1.1 pg / ml ) ( fig . 

there is no significant sex - related difference 
 in the plasma concentration of either orexin or leptin .
obese vs. control : p<0.001 
 for both indices . ) . similarly , plasma leptin concentration was higher in obese children ( 12.0  1.0 
 ng / ml ; p<0.001 ) than in the control children ( 5.2  0.4 ng / ml ) ( fig .
there is no significant sex - related difference 
 in the plasma concentration of either orexin or leptin .
table 3table 3 correlation between anthropometric indices and plasma level of orexin - a or 
 leptin in obese children ( n=47 ) summarizes relationships between the anthropometric indices and the plasma 
 level of orexin - a or leptin in obese children . the plasma orexin - a level was correlated 
 significantly with the waist - to - hip ratio only , while the leptin level was correlated with 
 percentage overweight , waist circumference and percentage body fat . the relationship between 
 plasma levels of orexin - a and leptin
. 2 correlation between plasma levels of orexin - a and leptin in obese children 
 ( n=47 ) .. there was a highly significant positive correlation between the two parameters . none 
 of the data on clinical blood biochemistry shown in table 2 was correlated with the plasma level of orexin - a or leptin .  
correlation between plasma levels of orexin - a and leptin in obese children 
 ( n=47 ) .
plasma levels of both orexin - a and leptin were higher in the obese than the control 
 children , and orexin - a was correlated positively with leptin .
however , both parameters were 
 correlated with only limited numbers of anthropometric indices , and with no other data of 
 clinical blood biochemistry .
( 18 ) reported that 
 plasma immunoreactive orexin - a level was 6.91  0.85 pg / ml in healthy adults after 
 extraction of orexin - a by sep pak chromatography from acidified plasma .
( 19 ) reported that the 
 basal level of orexin - a was 29.9  1.6 pg / ml without extraction , using the same commercial 
 kit as ours .
they also reported that the plasma orexin - a level increased to 38.947.9 pg / ml 
 during fasting for 710 days in the treatment of psychosomatic diseases in nonobese women 
 ( 19 ) . the reported level by arihara et 
 al .
( 19 ) were higher than ours . 
 in our study , orexin - a
reported ( 20 ) in subjects , whose ages 
 ranged from 23 to 79 yr , that plasma orexin - a level was higher in the elderly adults than in 
 the younger ones .
however , whether the difference in plasma concentrations between our study 
 and other studies is dependent on the ages of the subjects needs to be studied further .
the high level of orexin , which promotes appetite , in obese children , observed here , 
 implies that their appetite is not suppressed regardless of their obesity . the high plasma 
 level of orexin - a appeared to parallel the level of leptin in the present study . if the 
 orexinergic effect parallels that of leptin in the hypothalamic regulation of appetite , this 
 association can , at least partly , explain the apparent leptin resistance in the present 
 obese children .
however , this is unlikely because leptin is known to inhibit the orexinergic 
 pathway of acceleration of food intake in the lateral hypothalamic area .
adam et 
 al . reported ( 21 ) that the plasma orexin 
 level was inversely correlated with body mass index in the range of 2059 kg / m 
 in adults .
( 22 ) reported that plasma orexin - a level was positively correlated with either body 
 mass index or fat mass in lean and normal weight adults with chronic obstructive pulmonary 
 diseases .
patients with narcolepsy show a low concentration of orexin - a in cerebrospinal fluid ( 23 , 24 ) , however , 
 their plasma levels of orexin were reported to be either low ( 23 ) or normal ( 24 ) . around half of 
 the orexinergic neurons in the hypothalamus are under the inhibitory regulation of leptin . 

thus , orexin is secreted by fasting in order to conserve energy in the central nervous 
 system . whether the peripheral mechanism related to orexin is also regulated by leptin or 

this dual action of orexin in central and peripheral mechanisms needs to be 
 studied further . in the present study , plasma orexin - a level was correlated significantly with the 
 waist - to - hip ratio but not with waist circumference . on the other hand , the opposite was the 
 case with leptin .
lissner et al . ( 25 ) 
 reported in swedish women that hip circumference showed a health - promoting effect , and that 
 the effect was independent of the adverse health effect of waist circumference .
they 
 suggested that waist - to - hip ratio and waist circumference had mutually different 
 implications in health and longevity of men .
thus , the correlation profile of the two 
 indices may be different from each other .
 the present study was designed to determine the plasma level of orexin and its 
 relationship with other metabolic and anthropometric markers in obese children . 
 
 forty - seven obese japanese children , consisting of 31 boys and 16 girls , were enrolled in 
 the study . 
 their ages were 10.4  0.5 ( mean  s.e.m . ) yr , and their percentage overweight 
 was 42.9  1.9% . 
 blood was drawn after an overnight fast . 
 the age - matched control group 
 consisted of 26 nonobese children , 13 boys and 13 girls . 
 plasma orexin - a concentration was 
 higher in obese children ( 17.0  0.4 pg / ml ; p<0.001 ) than in the control children ( 13.5 
  1.1 pg / ml ) . similarly , plasma leptin concentration was higher in obese children ( 12.0  
 1.0 ng / ml ; p<0.001 ) than in the control children ( 5.2  0.4 ng / ml ) . 
 there was a highly 
 significant positive correlation between the two parameters in the obese children ( r=0.49 , 
 p<0.001 ) . 
 plasma orexin - a level was correlated significantly with waist - to - hip ratio , 
 while leptin level was correlated with percentage overweight , waist circumference and 
 percentage body fat in the obese children . 
 these results suggest that high plasma orexin - a 
 level parallels the leptin level in obese children . 