title: Insulin does not regulate glucose transport and metabolism in human endothelium.
abstract: BACKGROUND
  Although endothelial cells express insulin receptors, it is controversially discussed whether the endothelium represents an insulin-responsive tissue. Since available data are primarily restricted to animal endothelial cells, this study tested (i) whether insulin affects glucose metabolism in human endothelium; (ii) whether insulin sensitivity is different in micro- versus macrovascular endothelial cells; and (iii) whether glucose concentration in the incubation medium affects the cells' response to insulin.
  
  
  METHODS
  Human umbilical vein endothelial cells (HUVECs), human adult saphenous vein endothelial cells (HAVECs), human aortic endothelial cells (HAEC), and human retinal endothelial cells (HRECs) as well as human smooth muscle cells were incubated with/without insulin (0.3 nmol L(-1) or 1 micromol L(-1)). Glucose transport, glycogen synthesis, glycogen content, lactate release, and expression of phospho-Akt, Akt, and endothelial nitric oxide synthase (eNOS) were determined.
  
  
  RESULTS
  In HUVECs and HRECs, insulin (1 micromol L(-1)) increased (P < 0.05) eNOS expression by ~70% and doubled Akt phosphorylation, but the latter was by far more pronounced in human smooth muscle cells (+1093 +/- 500%, P < 0.05). In human smooth muscle cells, insulin (1 micromol L(-1)) stimulated glycogen synthesis by 67 +/- 11% (P < 0.01). In human micro- (HRECs) and macrovascular endothelial cells (HUVECs, HAVECs and HAECs), insulin, however, failed to stimulate glucose transport, glycogen synthesis, glycogen content, or lactate release under various conditions, i.e. after glucose deprivation or in medium with normal (5.5 mmol L(-1)) or high glucose (30 mmol L(-1)).
  
  
  CONCLUSIONS
  Insulin stimulated glycogen synthesis and Akt phosphorylation in human smooth muscle cells. In human micro- and macrovascular endothelial cells, insulin, however, failed to affect glucose uptake and metabolism under all experimental conditions applied, whereas it increased Akt phosphorylation and eNOS expression.
authors.affiliation: Medical University of Vienna, Vienna, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Artwohl
authors.forename: B
authors.initials: B
authors.lastname: Brunmair
authors.forename: C
authors.initials: C
authors.lastname: Fürnsinn
authors.forename: T
authors.initials: T
authors.lastname: Hölzenbein
authors.forename: G
authors.initials: G
authors.lastname: Rainer
authors.forename: A
authors.initials: A
authors.lastname: Freudenthaler
authors.forename: E M
authors.initials: EM
authors.lastname: Porod
authors.forename: N
authors.initials: N
authors.lastname: Huttary
authors.forename: S M
authors.initials: SM
authors.lastname: Baumgartner-Parzer
mesh_terms: D002478:Cells, Cultured; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051246:Glucose Transport Proteins, Facilitative / Q000187:drug effects*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects
chemical_list: D051246:Glucose Transport Proteins, Facilitative; D007004:Hypoglycemic Agents; D007328:Insulin; D052250:Nitric Oxide Synthase Type III; D005947:Glucose