title: Estrogen receptor antagonism uncovers gender-dimorphic suppression of whole body fat oxidation in humans: differential effects of tamoxifen on the GH and gonadal axes.
abstract: BACKGROUND
  Tamoxifen, a selective estrogen receptor modulator, suppresses GH secretion in women but not in men. It increases testosterone levels in men. As GH and testosterone stimulate fat metabolism, the metabolic consequences of tamoxifen may be greater in women than in men.
  
  
  OBJECTIVE
  To determine whether tamoxifen suppresses fat oxidation (Fox) to a greater degree in women than in men.
  
  
  METHODS
  An open-label study of ten healthy postmenopausal women and ten healthy men receiving 2-week treatment with tamoxifen (20  mg/day).
  GH response to arginine stimulation, serum levels of IGF1, testosterone and LH (men only), sex hormone binding globulin (SHBG) and whole body basal and postprandial Fox.
  
  
  RESULTS
  In women, tamoxifen significantly reduced the mean GH response to arginine stimulation (Δ -87%, P<0.05) and circulating IGF1 levels (Δ -23.5±5.4%, P<0.01). Tamoxifen reduced postprandial Fox in women (Δ -34.6±10.3%; P<0.05). In men, tamoxifen did not affect the GH response to arginine stimulation but significantly reduced mean IGF1 levels (Δ -24.8±6.1%, P<0.01). Tamoxifen increased mean testosterone levels (Δ 52±14.2%; P<0.01). Fox was not significantly affected by tamoxifen in men.
  
  
  CONCLUSIONS
  Tamoxifen attenuated the GH response to stimulation and reduced postprandial Fox in women but not in men. We conclude that at a therapeutic dose, the suppressive effect of tamoxifen on fat metabolism is gender-dependent. Higher testosterone levels may mitigate the suppression of GH secretion and Fox during tamoxifen treatment in men.
authors.affiliation: Department of EndocrinologyGarvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, AustraliaSchool of MedicineUniversity of Western Sydney, Sydney, New South Wales 2148, AustraliaThe University of NSWSydney, New South Wales 2052, AustraliaCentres for Health ResearchPrincess Alexandra Hospital, The University of Queensland, Brisbane, Queensland 4102, Australia Department of EndocrinologyGarvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, AustraliaSchool of MedicineUniversity of Western Sydney, Sydney, New South Wales 2148, AustraliaThe University of NSWSydney, New South Wales 2052, AustraliaCentres for Health ResearchPrincess Alexandra Hospital, The University of Queensland, Brisbane, Queensland 4102, Australia Department of EndocrinologyGarvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, AustraliaSchool of MedicineUniversity of Western Sydney, Sydney, New South Wales 2148, AustraliaThe University of NSWSydney, New South Wales 2052, AustraliaCentres for Health ResearchPrincess Alexandra Hospital, The University of Queensland, Brisbane, Queensland 4102, Australia.
authors.forename: Vita
authors.initials: V
authors.lastname: Birzniece
authors.affiliation: Department of EndocrinologyGarvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, AustraliaSchool of MedicineUniversity of Western Sydney, Sydney, New South Wales 2148, AustraliaThe University of NSWSydney, New South Wales 2052, AustraliaCentres for Health ResearchPrincess Alexandra Hospital, The University of Queensland, Brisbane, Queensland 4102, Australia Department of EndocrinologyGarvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, AustraliaSchool of MedicineUniversity of Western Sydney, Sydney, New South Wales 2148, AustraliaThe University of NSWSydney, New South Wales 2052, AustraliaCentres for Health ResearchPrincess Alexandra Hospital, The University of Queensland, Brisbane, Queensland 4102, Australia k.ho@uq.edu.au.
authors.forename: Ken K Y
authors.initials: KK
authors.lastname: Ho
mesh_terms: D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism; D000368:Aged; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005260:Female; D019382:Human Growth Hormone / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000187:drug effects / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects*; D007986:Luteinizing Hormone / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction / Q000187:drug effects*; D017698:Postmenopause; D012727:Sex Characteristics; D012738:Sex Hormone-Binding Globulin / Q000187:drug effects / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D013739:Testosterone / Q000378:metabolism*
chemical_list: D004965:Estrogen Antagonists; C583557:IGF1 protein, human; D012738:Sex Hormone-Binding Globulin; D013629:Tamoxifen; D019382:Human Growth Hormone; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone