title: Differential impact of type-1 and type-2 diabetes on control of heart rate in mice.
abstract: OBJECTIVE
  Cardiac autonomic dysfunction is a serious complication of diabetes. One consequence is disruption of the normal beat-to-beat regulation of heart rate (HR), i.e. HR variability (HRV). However, our understanding of the disease process has been limited by inconsistent HR/HRV data from previous animal studies. We hypothesized that differences in the method of measurement, time of day, and level of stress account for the differing results across studies. Thus, our aim was to systematically assess HR and HRV in two common diabetic mouse models.
  
  
  METHODS
  ECG radiotelemetry devices were implanted into db/db (type-2 diabetic), STZ-treated db/+ (type-1 diabetic), and control db/+ mice (n=4 per group). HR and HRV were analyzed over 24 h and during treadmill testing.
  
  
  RESULTS
  24 h analysis revealed that db/db mice had an altered pattern of circadian HR changes, and STZ-treated mice had reduced HR throughout. HRV measures linked to sympathetic control were reduced in db/db mice in the early morning and early afternoon, and partially reduced in STZ-treated mice. HR response to treadmill testing was blunted in both models.
  
  
  CONCLUSIONS
  It is important to consider both time of day and level of stress when assessing HR and HRV in diabetic mice. db/db mice may have altered circadian rhythm of sympathetic control of HR, whereas STZ-treated mice have a relative reduction. This study provides baseline data and a framework for HR analysis that may guide future investigations.
authors.affiliation: Department of Neurology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Stables
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Auerbach
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Whitesall
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Louis G
authors.initials: LG
authors.lastname: D'Alecy
authors.affiliation: Department of Neurology, University of Michigan, Ann Arbor, MI, USA. Electronic address: efeldman@umich.edu.
authors.forename: Eva L
authors.initials: EL
authors.lastname: Feldman
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000503:physiopathology*; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology*; D004195:Disease Models, Animal; D004452:Echocardiography; D004562:Electrocardiography; D005080:Exercise Test; D006339:Heart Rate / Q000235:genetics / Q000502:physiology*; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D013686:Telemetry
keywords: Autonomic nervous system; Diabetes complications; Disease models, animal; Heart rate