title: The effect of acute exercise on undercarboxylated osteocalcin and insulin sensitivity in obese men.
abstract: Acute exercise improves insulin sensitivity for hours after the exercise is ceased. The skeleton contributes to glucose metabolism and insulin sensitivity via osteocalcin (OC) in its undercarboxylated (ucOC) form in mice. We tested the hypothesis that insulin sensitivity over the hours after exercise is associated with circulating levels of ucOC. Eleven middle-aged (58.1 ± 2.2 years mean ± SEM), obese (body mass index [BMI] = 33.1 ± 1.4 kg/m(2) ) nondiabetic men completed a euglycemic-hyperinsulinemic clamp at rest (rest-control) and at 60 minutes after exercise (4 × 4 minutes of cycling at 95% of HRpeak ). Insulin sensitivity was determined by glucose infusion rate relative to body mass (GIR, mL/kg/min) as well as GIR per unit of insulin (M-value). Blood samples and five muscle biopsies were obtained; two at the resting-control session, one before and one after clamping, and three in the exercise session, at rest, 60 minutes after exercise, and after the clamp. Exercise increased serum ucOC (6.4 ± 2.1%, p = 0.013) but not total OC (p > 0.05). Blood glucose was ∼6% lower and insulin sensitivity was ∼35% higher after exercise compared with control (both p < 0.05). Phosphorylated (P)-AKT (Ak thymoma) was higher after exercise and insulin compared with exercise alone (no insulin) and insulin alone (no exercise, all p < 0.05). In a multiple-linear regression including BMI, age, and aerobic fitness, ucOC was associated with whole-body insulin sensitivity at rest (β = 0.59, p = 0.023) and after exercise (β = 0.66, p = 0.005). Insulin sensitivity, after acute exercise, is associated with circulating levels of ucOC in obese men. Whether ucOC has a direct effect on skeletal muscle insulin sensitivity after exercise is yet to be determined.
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), College of Sport and Exercise Science, Victoria University, Melbourne, Australia; Australian Institute of Musculoskeletal Science, NorthWest Academic Centre, The University of Melbourne, Western Health, Melbourne, Australia.
authors.forename: Itamar
authors.initials: I
authors.lastname: Levinger
authors.forename: George
authors.initials: G
authors.lastname: Jerums
authors.forename: Nigel K
authors.initials: NK
authors.lastname: Stepto
authors.forename: Lewan
authors.initials: L
authors.lastname: Parker
authors.forename: Fabio R
authors.initials: FR
authors.lastname: Serpiello
authors.forename: Glenn K
authors.initials: GK
authors.lastname: McConell
authors.forename: Mitchell
authors.initials: M
authors.lastname: Anderson
authors.forename: David L
authors.initials: DL
authors.lastname: Hare
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Byrnes
authors.forename: Peter R
authors.initials: PR
authors.lastname: Ebeling
authors.forename: Ego
authors.initials: E
authors.lastname: Seeman
mesh_terms: D000818:Animals; D015992:Body Mass Index; D015444:Exercise; D015309:Glucose Clamp Technique; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D051379:Mice; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology; D009765:Obesity / Q000097:blood / Q000503:physiopathology; D015675:Osteocalcin; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism
chemical_list: D015675:Osteocalcin; D051057:Proto-Oncogene Proteins c-akt
keywords: BONE METABOLISM; EXERCISE; GLYCEMIC CONTROL; OBESITY; UNDERCARBOXYLATED OSTEOCALCIN