title: Chronic exposure to a high-fat diet affects stress axis function differentially in diet-induced obese and diet-resistant rats.
abstract: OBJECTIVE
  Consumption of a high-fat (HF) diet is a contributing factor for the development of obesity. HF diet per se acts as a stressor, stimulating hypothalamo-pituitary-adrenal (HPA) axis activity resulting in elevated glucocorticoid levels; however, the mechanism behind this activation is unclear. We hypothesized that consumption of an HF diet activates HPA axis by increasing norepinephrine (NE) in the paraventricular nucleus (PVN) of the hypothalamus, leading to elevation in corticotrophin-releasing hormone (CRH) concentration in the median eminence (ME) resulting in elevated serum corticosterone (CORT).
  
  
  METHODS
  To test this hypothesis, diet-induced obese (DIO) and diet-resistant (DR) rats were exposed to either chow or HF diet for 6 weeks.
  
  
  METHODS
  At the end of 6 weeks, NE in the PVN was measured using HPLC, CRH in the ME, and CORT and leptin levels in the serum were measured using RIA and ELISA, respectively. The gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in NE synthesis, and leptin receptor in brainstem noradrenergic nuclei were also measured.
  
  
  RESULTS
  HF diet increased PVN NE in both DIO and DR rats (P<0.05). However, this was accompanied by increases in CRH and CORT secretion only in DR animals, but not in DIO rats. Leptin receptor mRNA levels in the brainstem noradrenergic areas were not affected in both DIO and DR rats. However, HF diet increased TH mRNA levels only in DIO rats.
  
  
  CONCLUSIONS
  Significant differences occur in all the arms of HPA axis function between DIO and DR rats. Further studies are needed to determine whether this could be a causative factor or a consequence to obesity.
authors.affiliation: Neuroendocrine Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Shin
authors.forename: S M J
authors.initials: SM
authors.lastname: MohanKumar
authors.forename: M P
authors.initials: MP
authors.lastname: Sirivelu
authors.forename: K J
authors.initials: KJ
authors.lastname: Claycombe
authors.forename: J R
authors.initials: JR
authors.lastname: Haywood
authors.forename: G D
authors.initials: GD
authors.lastname: Fink
authors.forename: P S
authors.initials: PS
authors.lastname: MohanKumar
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D003346:Corticotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D007031:Hypothalamus / Q000378:metabolism / Q000503:physiopathology*; D020738:Leptin / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000235:genetics / Q000378:metabolism*; D009765:Obesity / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D010913:Pituitary-Adrenal System / Q000378:metabolism / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D020738:Leptin; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D009638:Norepinephrine