title: Progressive hyperglycemia across the glucose tolerance continuum in older obese adults is related to skeletal muscle capillarization and nitric oxide bioavailability.
abstract: BACKGROUND
  Reduced tissue nutrient exposure may aid in the progression of glucose intolerance.
  
  
  OBJECTIVE
  The aim of the study was to examine peripheral tissue glucose disposal in relation to muscle capillarization and plasma nitric oxide bioavailability.
  
  
  METHODS
  Participants were carefully matched for age, adiposity, and lipid status and stratified into normal (n = 20), impaired (n = 20), and type 2 diabetic (n = 20) glucose-tolerant groups.
  
  
  METHODS
  The study was conducted in an outpatient setting at a Clinical Research Unit.
  
  
  METHODS
  Older, obese men and women (n = 60; age, 65 ± 1 yr; body mass index, 32.7 ± 0.5 kg/m(2)) participated in the study.
  
  
  METHODS
  We performed a cross-sectional study.
  
  
  METHODS
  Body composition, energy metabolism, aerobic fitness (maximum oxygen consumption), insulin sensitivity (glucose clamp), vastus lateralis muscle morphology, and plasma nitric oxide were assessed.
  
  
  RESULTS
  Although subjects were identical with respect to age, body composition, energy expenditure, and lipid status, insulin-stimulated glucose disposal and maximum oxygen consumption showed progressive decline with increasing glucose intolerance. Muscle fiber type composition and mitochondrial density were not different between groups. However, capillary density markedly declined with advancing glucose intolerance (1.86 ± 0.31, 1.70 ± 0.28, 1.42 ± 0.24 capillary/fiber; P < 0.05), a trend that was mirrored by fasting plasma nitric oxide concentrations (26.3 ± 3.6, 19.8 ± 2.3, 15.2 ± 2.1 μmol/liter; P < 0.05). Furthermore, skeletal muscle capillary density correlated with insulin sensitivity (r = 0.65; P < 0.001).
  
  
  CONCLUSIONS
  Impaired muscle capillarization and reduced nutrient exposure to the metabolizing tissue may play a major role in the progression of insulin resistance across the glucose tolerance continuum, independent of age, adiposity, lipid status, and resting energy metabolism. These data also highlight plasma nitric oxide as a potential surrogate marker of these impairments and may be indicative of the progression toward type 2 diabetes.
authors.affiliation: Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio 44195, USA.
authors.forename: Thomas P J
authors.initials: TP
authors.lastname: Solomon
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Haus
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Li
authors.forename: John P
authors.initials: JP
authors.lastname: Kirwan
mesh_terms: D000368:Aged; D015308:Anaerobic Threshold / Q000502:physiology; D001774:Blood Chemical Analysis; D001823:Body Composition / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D005947:Glucose / Q000378:metabolism; D018149:Glucose Intolerance / Q000150:complications / Q000473:pathology*; D005951:Glucose Tolerance Test; D006801:Humans; D006943:Hyperglycemia / Q000150:complications / Q000473:pathology*; D007333:Insulin Resistance / Q000502:physiology; D008297:Male; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply*; D009569:Nitric Oxide / Q000378:metabolism*; D009765:Obesity / Q000150:complications / Q000473:pathology*; D017698:Postmenopause / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D009569:Nitric Oxide; D005947:Glucose