title: Constriction of porcine retinal arterioles induced by endothelin-1 and the thromboxane analogue U46619 in vitro decreases with increasing vascular branching level.
abstract: OBJECTIVE
  The retinal blood flow depends on the diameter of retinal arterioles, but diameter changes in these vessels have hitherto only been assessed in vessels larger than approximately 100 μm. Therefore, a new method was developed for studying diameter changes along the vascular tree of arterioles in whole perfused segments of porcine retinas, and the effect of known vasoconstrictors on the diameter of retinal arterioles at different branching levels were studied.
  
  
  METHODS
  Thirty-four whole-mounted porcine retinas were placed in a specially designed tissue chamber. On the basis of video recordings through an inverted microscope, the diameter of retinal arterioles was measured at five different branching levels before and after addition of a high potassium concentration, or increasing concentrations of endothelin-1, the prostaglandin analogue U46619, noradrenaline or none (time controls).
  
  
  RESULTS
  The baseline diameter ranged from 136 μm (95% CI 132-140 μm) for 1st order arterioles to 33 μm (95% CI 21-44 μm) for 5th order arterioles. In 1st order arterioles, endothelin produced 56.6% (95% CI 47.6-64.0) and U46619 14.6% (95% CI 5.7-22.6) relative constriction compared with baseline, which for both compounds decreased significantly with increasing branching level (p<0.0001 and p<0.0001, respectively). The change in diameter during addition of noradrenaline did not differ significantly from the time controls (p=0.07).
  
  
  CONCLUSIONS
  The effect of retinal vasoconstrictors differs among larger and smaller arterioles. The study highlights the need for investigating diameter regulation in smaller retinal arterioles as a basis for understanding normal and pathological changes in retinal blood flow.
authors: Department of Ophthalmology, Aarhus University Hospital, Aarhus, DenmarkDepartment of Biomedicine, Aarhus University, Aarhus, Denmark.
authors: Maria Skytte
authors: MS
authors: Torring
authors: Christian
authors: C
authors: Aalkjaer
authors: Toke
authors: T
authors: Bek
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D019332:Endothelin-1 / Q000494:pharmacology*; D012039:Regional Blood Flow / Q000187:drug effects*; D012161:Retinal Artery / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D012164:Retinal Diseases / Q000473:pathology / Q000503:physiopathology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014741:Video Recording
chemical_list: D019332:Endothelin-1; D014662:Vasoconstrictor Agents; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid
keywords: U46619; endothelin-1; noradrenaline; retinal vascular diameter; vasoconstrictors; whole-mount retina