title: Effects of insulin on retinal and pulsatile choroidal blood flow in humans.
abstract: BACKGROUND
  Insulin induces vasodilation in several tissues, including skeletal muscle and kidneys.
  
  
  OBJECTIVE
  To investigate whether insulin may contribute to ocular blood flow regulation.
  
  
  METHODS
  The study was performed in a balanced, randomized, placebo-controlled, single-masked, 3-way, crossover design in 9 healthy male subjects. Each subject received 2 doses of insulin (1.5 or 3 mU/kg per minute) or placebo on 3 different study days. Measurements of fundus pulsation amplitude with laser interferometry to assess pulsatile choroidal blood flow, of retinal blood flow with the blue-field entoptic technique, and of mean blood flow velocity in the ophthalmic artery with Doppler sonography were performed under euglycemic clamp conditions over 120 minutes.
  
  
  RESULTS
  Hyperinsulinemia significantly increased fundus pulsation amplitude (1.5 mU/kg per minute: 8.7% +/- 1.1% vs baseline; 3 mU/kg per minute: 13.2% +/- 2.3% vs baseline; P<.001 vs placebo [analysis of variance]) and mean blood flow velocity (1.5 mU/kg per minute: 10.0% +/- 4.3% vs baseline; 3 mU/kg per minute: 6.6% +/- 3.5% vs baseline; P = .03 vs placebo). Retinal blood flow did not increase during administration of insulin (1.5 mU/kg per minute: 6.4% +/- 8.0% vs baseline; 3 mU/kg per minute: 8.0% +/- 5.1% vs baseline; P = .99 vs placebo). Neither the effect in the choroid nor that in the ophthalmic artery was dose-dependent.
  
  
  CONCLUSIONS
  Hyperinsulinemia significantly increases choroidal blood flow and mean blood flow velocity in the ophthalmic artery. By contrast, retinal blood flow was not influenced by hyperinsulinemia. The maximum effective dose of insulin for ocular hemodynamics is likely to be within the physiological range.
authors.affiliation: Department of Clinical Pharmacology, Vienna University, Austria.
authors.forename: K
authors.initials: K
authors.lastname: Polak
authors.forename: S
authors.initials: S
authors.lastname: Dallinger
authors.forename: E
authors.initials: E
authors.lastname: Polska
authors.forename: O
authors.initials: O
authors.lastname: Findl
authors.forename: H G
authors.initials: HG
authors.lastname: Eichler
authors.forename: M
authors.initials: M
authors.lastname: Wolzt
authors.forename: L
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D002829:Choroid / Q000098:blood supply*; D018592:Cross-Over Studies; D006801:Humans; D006946:Hyperinsulinism / Q000503:physiopathology; D007328:Insulin / Q000494:pharmacology*; D007368:Interferometry; D017078:Laser-Doppler Flowmetry; D008297:Male; D009880:Ophthalmic Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D011673:Pulsatile Flow / Q000502:physiology*; D012171:Retinal Vessels / Q000502:physiology*; D016037:Single-Blind Method; D014463:Ultrasonography
chemical_list: D007328:Insulin