title: Measurement of retinal blood flow rate in diabetic rats: disparity between techniques due to redistribution of flow.
abstract: OBJECTIVE
  Reports of altered retinal blood flow in experimental models of type I diabetes have provided contrasting results, which leads to some confusion as to whether flow is increased or decreased. The purpose of our study was to evaluate early diabetes-induced changes in retinal blood flow in diabetic rats, using two distinctly different methods.
  
  
  METHODS
  Diabetes was induced by injection of streptozotocin (STZ), and retinal blood flow rate was measured under anesthesia by a microsphere infusion technique, or by an index of flow based on the mean circulation time between arterioles and venules. Measurements in STZ rats were compared to age-matched nondiabetic controls. In addition, the retinal distribution of fluorescently-labeled red blood cells (RBCs) was viewed by confocal microscopy in excised flat mounts.
  
  
  RESULTS
  Retinal blood flow rate was found to decrease by approximately 33% in the STZ rats compared to controls (P < 0.001) as assessed by the microsphere technique. However, in striking contrast, the mean circulation time through the retina was found to be almost 3× faster in the STZ rats (P < 0.01). This contradiction could be explained by flow redistribution through the superficial vessels of the diabetic retina, with this possibility supported by our observation of significantly fewer RBCs flowing through the deeper capillaries.
  
  
  CONCLUSIONS
  We conclude that retinal blood flow rate is reduced significantly in the diabetic rat, with a substantial decrease of flow through the capillaries due to shunting of blood through the superficial layer, allowing rapid transit from arterioles to venules.
authors.affiliation: Louisiana State University Health Sciences Center in Shreveport, Department of Molecular and Cellular Physiology, Shreveport, LA 71130-3932, USA.
authors.forename: Wendy
authors.initials: W
authors.lastname: Leskova
authors.forename: Megan N
authors.initials: MN
authors.lastname: Watts
authors.forename: Patsy R
authors.initials: PR
authors.lastname: Carter
authors.forename: Randa S
authors.initials: RS
authors.lastname: Eshaq
authors.forename: Norman R
authors.initials: NR
authors.lastname: Harris
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D003911:Dextrans; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004912:Erythrocytes / Q000502:physiology; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives; D005456:Fluorescent Dyes; D017078:Laser-Doppler Flowmetry; D008297:Male; D018613:Microscopy, Confocal; D008863:Microspheres; D051381:Rats; D017208:Rats, Wistar; D012171:Retinal Vessels / Q000502:physiology*
chemical_list: D003911:Dextrans; D005456:Fluorescent Dyes; C015219:fluorescein isothiocyanate dextran; D016650:Fluorescein-5-isothiocyanate