title: Sphincter activity in retinal arterioles feeding the deeper capillary layer in pig.
abstract: OBJECTIVE
  To determine whether a sphincter-like control point is present in 90 degrees branches of the retinal vasculature. Such a control point could selectively control retinal blood flow to the deeper capillary layers.
  
  
  METHODS
  A microperfusion system was used in which porcine retinal arteries with intact branches were cannulated and perfused intraluminally at physiological flow rates. The vasoactive response of the proximal and distal regions of either 90 degrees -or Y-type branches to intraluminal potassium (124 mM) were monitored simultaneously in real-time.
  
  
  RESULTS
  The proximal region of the 90 degrees branches demonstrated a localized vasoconstriction when compared to the more distal region (p < 0.0001). In contrast, the Y branches contracted evenly along their length.
  
  
  CONCLUSIONS
  The localized vasoactivity near the branch point of the 90 degrees -type branches may explain previous observations of so-called sphincter-like activity in these vessels. These sphincters may selectively regulate blood flow to the deeper retinal capillary layer.
authors.affiliation: Centre for Ophthalmology and Visual Science, Lions Eye Institute, The University of Western Australia, Nedlands, Perth, Australia. dyyu@cyllene.uwa.edu.au
authors.forename: Dao-Yi
authors.initials: DY
authors.lastname: Yu
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Cringle
authors.forename: Er-Ning
authors.initials: EN
authors.lastname: Su
authors.forename: Paula K
authors.initials: PK
authors.lastname: Yu
mesh_terms: D000818:Animals; D001160:Arterioles / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012039:Regional Blood Flow / Q000502:physiology; D012171:Retinal Vessels / Q000502:physiology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D011188:Potassium