title: Lack of Day/Night variation in fibroblast growth factor 21 levels in young healthy men.
abstract: BACKGROUND
  Fibroblast growth factor (FGF) 21 is an endocrine factor with an emerging role as a metabolic regulator. We previously reported the presence of a significant day/night variation of FGF-21 in energy-replete, healthy female subjects. However the day/night patterns of secretion in male subjects remain to be fully elucidated. To elucidate day/night pattern of FGF-21 levels in male subjects in the energy-replete state, its relationship to FFA and to investigate whether a sexual dimorphism exists in FGF-21 physiology.
  
  
  METHODS
  Eight healthy lean male subjects were studied for up to 5 days while on an isocaloric diet. Blood samples were obtained for measurement of FGF-21 and free fatty acids (FFA) hourly from 0800 AM on day 4 till 0800AM on day 5.
  
  
  RESULTS
  FGF-21 did not exhibit any statistically significant day/night variation pattern of circulating FGF-21 levels during the isocaloric fed state in male subjects. FGF-21 levels in male subjects are closely cross-correlated with FFA levels, similar to female subjects.
  
  
  CONCLUSIONS
  A sexual dimorphism exists in FGF-21 physiology; that as opposed to female subjects, no significant day/night variation exists in FGF-21 rhythm in male subjects in the energy-replete state. Circulating pattern of FGF-21, similar to the female subjects, was highly cross-correlated to the FFA levels in the male subjects, signifying that the sexual dimorphism in FGF-21 physiology may be related to the differing lipid metabolism in both the genders.
authors.affiliation: Division of Endocrinology, Diabetes & Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: J-P
authors.initials: JP
authors.lastname: Foo
authors.affiliation: 1] Division of Endocrinology, Diabetes & Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA [2] Section of Endocrinology, Boston VA Healthcare System, Harvard Medical School, Boston, MA, USA [3] Department of Medicine, Boston Medical Center, Boston University, Boston, MA, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Aronis
authors.affiliation: 1] Division of Endocrinology, Diabetes & Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA [2] Section of Endocrinology, Boston VA Healthcare System, Harvard Medical School, Boston, MA, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Chamberland
authors.affiliation: 1] Division of Endocrinology, Diabetes & Metabolism, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA [2] Section of Endocrinology, Boston VA Healthcare System, Harvard Medical School, Boston, MA, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Mantzoros
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005260:Female; D005346:Fibroblast Growth Factors / Q000097:blood*; D064368:Healthy Volunteers; D006801:Humans; D020738:Leptin / Q000097:blood*; D008297:Male; D012727:Sex Characteristics; D015398:Signal Transduction; D015431:Weight Loss; D055815:Young Adult
chemical_list: D005230:Fatty Acids, Nonesterified; D020738:Leptin; C414620:fibroblast growth factor 21; D005346:Fibroblast Growth Factors