title: Chronic exercise increases plasma brain-derived neurotrophic factor levels, pancreatic islet size, and insulin tolerance in a TrkB-dependent manner.
abstract: BACKGROUND
  Physical exercise improves glucose metabolism and insulin sensitivity. Brain-derived neurotrophic factor (BDNF) enhances insulin activity in diabetic rodents. Because physical exercise modifies BDNF production, this study aimed to investigate the effects of chronic exercise on plasma BDNF levels and the possible effects on insulin tolerance modification in healthy rats.
  
  
  METHODS
  Wistar rats were divided into five groups: control (sedentary, C); moderate- intensity training (MIT); MIT plus K252A TrkB blocker (MITK); high-intensity training (HIT); and HIT plus K252a (HITK). Training comprised 8 weeks of treadmill running. Plasma BDNF levels (ELISA assay), glucose tolerance, insulin tolerance, and immunohistochemistry for insulin and the pancreatic islet area were evaluated in all groups. In addition, Bdnf mRNA expression in the skeletal muscle was measured.
  
  
  RESULTS
  Chronic treadmill exercise significantly increased plasma BDNF levels and insulin tolerance, and both effects were attenuated by TrkB blocking. In the MIT and HIT groups, a significant TrkB-dependent pancreatic islet enlargement was observed. MIT rats exhibited increased liver glycogen levels following insulin administration in a TrkB-independent manner.
  
  
  CONCLUSIONS
  Chronic physical exercise exerted remarkable effects on insulin regulation by inducing significant increases in the pancreatic islet size and insulin sensitivity in a TrkB-dependent manner. A threshold for the induction of BNDF in response to physical exercise exists in certain muscle groups. To the best of our knowledge, these are the first results to reveal a role for TrkB in the chronic exercise-mediated insulin regulation in healthy rats.
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Alberto
authors.initials: A
authors.lastname: Jiménez-Maldonado
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Elena Roces
authors.initials: ER
authors.lastname: de Álvarez-Buylla
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Sergio
authors.initials: S
authors.lastname: Montero
authors.affiliation: Facultad de Medicina, Universidad de Colima, Colima, México.
authors.forename: Valery
authors.initials: V
authors.lastname: Melnikov
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Elena
authors.initials: E
authors.lastname: Castro-Rodríguez
authors.affiliation: Depto de Patología, Instituto Nacional de Nutrición y Ciencias Médicas "Salvador Zubirán," México City, México D.F.
authors.forename: Armando
authors.initials: A
authors.lastname: Gamboa-Domínguez
authors.affiliation: Facultad de Medicina, Universidad de Colima, Colima, México.
authors.forename: Alejandrina
authors.initials: A
authors.lastname: Rodríguez-Hernández
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Mónica
authors.initials: M
authors.lastname: Lemus
authors.affiliation: Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, México.
authors.forename: Jesús Muñiz
authors.initials: JM
authors.lastname: Murguía
mesh_terms: D000818:Animals; D019540:Area Under Curve; D019208:Brain-Derived Neurotrophic Factor / Q000097:blood* / Q000235:genetics / Q000378:metabolism; D005951:Glucose Tolerance Test; D006003:Glycogen / Q000378:metabolism; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007333:Insulin Resistance; D007515:Islets of Langerhans / Q000033:anatomy & histology / Q000473:pathology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D009929:Organ Size; D010805:Physical Conditioning, Animal; D012333:RNA, Messenger / Q000378:metabolism; D012372:ROC Curve; D051381:Rats; D017208:Rats, Wistar; D020813:Receptor, trkB / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D007328:Insulin; D012333:RNA, Messenger; D006003:Glycogen; D020813:Receptor, trkB