title: Neuropeptide Y mediates the short-term hypometabolic effect of estrogen deficiency in mice.
abstract: BACKGROUND
  Estrogen deficiency increases body weight or total and central adiposity and decreases energy expenditure. Hypothalamic neuropeptide Y (NPY) expression is altered by estrogen deficiency in rodents, but the long-term consequences on energy homeostasis are unknown.
  
  
  OBJECTIVE
  To investigate the role of NPY in the changes in energy expenditure and physical activity, as well as the associated changes in body weight and composition in response to short-term and long-term estrogen deficiency.
  
  
  METHODS
  Sham and ovariectomy (OVX) operations were performed at 8 weeks of age in wild-type (WT) and NPY(-/-) mice. Energy expenditure, physical activity, body composition and weight, as well as food intake were measured at 10-18 days (short-term) and 46-54 days (long-term) after OVX.
  
  
  RESULTS
  OVX influences energy homeostasis differently at early compared with later time-points. At the early but not the late time point, OVX in WT mice reduced oxygen consumption and energy expenditure and tended to reduce resting metabolic rate. Interestingly, these effects of short-term estrogen deficiency were ablated by NPY deletion, with NPY(-/-) mice exhibiting significant increases in energy expenditure and resting metabolic rate. In addition to these hypermetabolic effects, OVX NPY(-/-) mice exhibited significantly lower body weight and whole-body fat mass relative to OVX WT controls at the short-term but not the long-term time point. Food intake and physical activity were unaltered by OVX, but NPY(-/-) mice exhibited significant reductions in these parameters relative to WT.
  
  
  CONCLUSIONS
  The effects of estrogen deficiency to reduce energy metabolism are transient, and NPY is critical to this effect as well as the early OVX-induced obesity.
authors.affiliation: Osteoporosis and Bone Biology, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Zengin
authors.forename: A D
authors.initials: AD
authors.lastname: Nguyen
authors.forename: I P L
authors.initials: IP
authors.lastname: Wong
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.forename: R F
authors.initials: RF
authors.lastname: Enriquez
authors.forename: J A
authors.initials: JA
authors.lastname: Eisman
authors.forename: H
authors.initials: H
authors.lastname: Herzog
authors.forename: P A
authors.initials: PA
authors.lastname: Baldock
authors.forename: A
authors.initials: A
authors.lastname: Sainsbury
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D001835:Body Weight; D002151:Calorimetry; D004435:Eating; D004734:Energy Metabolism; D004967:Estrogens / Q000172:deficiency* / Q000378:metabolism; D005260:Female; D006706:Homeostasis; D007031:Hypothalamus / Q000378:metabolism*; D051379:Mice; D009478:Neuropeptide Y / Q000378:metabolism*; D010052:Ovariectomy; D010805:Physical Conditioning, Animal
chemical_list: D004967:Estrogens; D009478:Neuropeptide Y