title: Acute hyperglycemia attenuates endothelium-dependent vasodilation in humans in vivo.
abstract: BACKGROUND
  Endothelial function is impaired in patients with diabetes mellitus. However, the factors contributing to this defect are currently unknown. Hyperglycemia attenuates endothelium-dependent relaxation in normal rabbit arteries in vitro and rat arterioles in vivo. Accordingly, this study examined the effect of acute hyperglycemia on endothelium-dependent vasodilation in nondiabetic humans in vivo.
  
  
  RESULTS
  Endothelium-dependent vasodilation was assessed through brachial artery infusion of methacholine chloride both before and during 6 hours of local hyperglycemia (300 mg/dL) achieved by intra-arterial infusion of 50% dextrose. Forearm blood flow was determined by plethysmography. In a group of 10 subjects, there was a trend toward attenuated methacholine-mediated vasodilation during hyperglycemia compared with euglycemia (P=.07 by ANOVA; maximal response, 13.3+/-2.8 versus 14.7+/-1.5 mL x min(-1) x 100 mL(-1), respectively). In these subjects, the systemic serum insulin levels increased significantly during the dextrose infusion (P<.001). To eliminate the confounding vasoactive effects of insulin, the protocol was repeated during systemic infusion of octreotide (30 ng x kg(-1) x min(-1)) to inhibit pancreatic secretion of insulin. In these subjects (n=10), hyperglycemia significantly attenuated the forearm blood flow response to methacholine (P<.01 by ANOVA; maximal response, 16.9+/-2.5 before versus 12.7+/-1.8 mL x min(-1) x 100 mL(-1) during hyperglycemia). Methacholine-mediated vasodilation was not attenuated by an equimolar infusion of mannitol (P>.40), nor did hyperglycemia reduce endothelium-independent vasodilation to verapamil (P>.50).
  
  
  CONCLUSIONS
  Acute hyperglycemia impairs endothelium-dependent vasodilation in healthy humans in vivo. This finding suggests that elevated glucose may contribute to the endothelial dysfunction observed in patients with diabetes mellitus.
authors.affiliation: Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, Mass 02115, USA.
authors.forename: S B
authors.initials: SB
authors.lastname: Williams
authors.forename: A B
authors.initials: AB
authors.lastname: Goldfine
authors.forename: F K
authors.initials: FK
authors.lastname: Timimi
authors.forename: H H
authors.initials: HH
authors.lastname: Ting
authors.forename: M A
authors.initials: MA
authors.lastname: Roddy
authors.forename: D C
authors.initials: DC
authors.lastname: Simonson
authors.forename: M A
authors.initials: MA
authors.lastname: Creager
mesh_terms: D000208:Acute Disease; D000328:Adult; D003920:Diabetes Mellitus / Q000503:physiopathology; D004730:Endothelium, Vascular / Q000502:physiology*; D005260:Female; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology*; D008297:Male; D016210:Methacholine Chloride / Q000494:pharmacology; D015282:Octreotide / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology
chemical_list: D016210:Methacholine Chloride; D014700:Verapamil; D015282:Octreotide