title: Adenosine-mediated autoregulation of retinal arteriolar tone in the piglet.
abstract: OBJECTIVE
  To determine if the purine vasodilator adenosine participates in mediating autoregulatory dilations of the retinal microcirculation in vivo.
  
  
  METHODS
  The retinal microcirculation of isoflurane-anesthetized newborn pigs was observed by videomicroscopy (x310). Systemic hypoxia (PaO2 = 24 +/- 1 mm Hg; n = 8) or hemorrhagic hypotension (MABP = 41 +/- 1 mm Hg; n = 5) was induced, and the effect of intravitreal microsuffusion of 0.4 nmol of the adenosine receptor antagonist 8-sulfophenyltheophylline (8SPT) on retinal arteriolar dilations resulting from these stimuli were measured. The effect of potentiation of endogenous interstitial adenosine concentrations with 0.2 nmol 4-nitrobenzyl-6-thioinosine (NBTI) on the response to hypotension (MABP = 43 +/- 2 mm Hg; n = 4) was also determined.
  
  
  RESULTS
  The significant vasodilatative response of the retinal arterioles to systemic hypoxia (36 +/- 8% increase in diameter above baseline; P = 0.0012) was attenuated 55% (P < 0.0001) by the adenosine antagonist 8SPT. Similarly, the significant arteriolar vasodilation induced by systemic hypotension (29 +/- 3% increase in diameter; P < 0.0001) was inhibited 76% by 8SPT (P = 0.0002). When adenosine reuptake was inhibited with NBTI, the arteriolar dilation induced by hypotension (32 +/- 5% increase in diameter; P = 0.0234) was potentiated 100% (P = 0.0117).
  
  
  CONCLUSIONS
  Our finding that inhibition or potentiation of endogenous adenosine action uniquely affected retinal arteriolar dilatative responses to hypoxia and hypotension suggests that adenosine is a key participant in mediating autoregulatory adjustments in retinal blood flow in the eye of the newborn.
authors.affiliation: Department of Neurology and Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri.
authors.forename: J M
authors.initials: JM
authors.lastname: Gidday
authors.forename: T S
authors.initials: TS
authors.lastname: Park
mesh_terms: D000241:Adenosine / Q000502:physiology*; D000818:Animals; D001160:Arterioles / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D008833:Microcirculation; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D015814:Ocular Hypotension / Q000503:physiopathology; D010101:Oxygen Consumption; D011983:Receptors, Purinergic / Q000187:drug effects; D012161:Retinal Artery / Q000502:physiology*; D013552:Swine; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014741:Video Recording
chemical_list: D011983:Receptors, Purinergic; D013868:Thioinosine; C031433:8-(4-sulfophenyl)theophylline; D013806:Theophylline; C001789:4-nitrobenzylthioinosine; D000241:Adenosine