title: Haemoglobin and vascular function in the human retinal vascular bed.
abstract: OBJECTIVE
  Haemoglobin is a potential nitric oxide (NO) scavenger. Haemoglobin is associated with blood viscosity and the red blood cell free layer width of microvessels that impact on shear stress in the microcirculation. We hypothesized that haemoglobin modulates retinal vascular function.
  
  
  METHODS
  In 139 nondiabetic male patients with haemoglobin levels within the normal range, the vasodilatatory response of retinal capillary blood flow (RCF) to flicker light exposure and the vasoconstrictor response of RCF to infusion of NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA) were assessed. The latter, because of the selective nature of L-NMMA, reflects a parameter of basal NO activity of retinal vasculature. Examinations of retinal parameters were performed noninvasively and in vivo using scanning laser Doppler flowmetry.
  
  
  RESULTS
  Patients with haemoglobin greater or equal the median revealed reduced increase of RCF to flicker light exposure (2.83 ± 12 vs. 9.52 ± 14 (%), P adjusted = 0.002), and greater decrease of RCF to L-NMMA infusion (-7.35 ± 13 vs. -0.92 ± 14 (%), P adjusted = 0.008), compared with patients with haemoglobin below the median. Haemoglobin was negatively related to the percentage change of RCF to flicker light exposure (r = -0.249, P = 0.004) and to L-NMMA infusion (r = -0.201, P = 0.018). In multiple linear regression analysis haemoglobin was an independent determinant of the percentage change of RCF to flicker light exposure (model 1: ß = -0.278, P = 0.003 and model 2: ß = -0.283, P = 0.002) and to L-NMMA infusion (model 1: ß = -0.256, P = 0.005 and model 2: ß = -0.269, P = 0.004).
  
  
  CONCLUSIONS
  Haemoglobin emerged as an independent determinant of vascular function in the human retinal vascular bed.
authors: Department of Nephrology and Hypertension, University of Erlangen-Nürnberg, Bavaria, Germany.
authors: Martin
authors: M
authors: Ritt
authors: Joanna M
authors: JM
authors: Harazny
authors: Stephanie
authors: S
authors: Schmidt
authors: Ulrike
authors: U
authors: Raff
authors: Christian
authors: C
authors: Ott
authors: Georg
authors: G
authors: Michelson
authors: Roland E
authors: RE
authors: Schmieder
mesh_terms: D000328:Adult; D005425:Flicker Fusion; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008027:Light; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow; D012171:Retinal Vessels / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation; D019323:omega-N-Methylarginine / Q000494:pharmacology
chemical_list: D006454:Hemoglobins; D019323:omega-N-Methylarginine