title: Role of endogenous adenosine as a modulator of syncope induced during tilt testing.
abstract: BACKGROUND
  Previous reports that used head-up tilt testing and adenosine administration have suggested that adenosine may be an important endogenous mediator that may trigger a vasovagal response in susceptible patients. However, little is known regarding endogenous adenosine plasma levels (APLs) during vasovagal syncope provoked by tilt testing. The aim of this study was to determine whether APLs differ in patients with a positive head-up tilt test compared with those with a negative test and whether APLs are modified during tilt-induced vasovagal syncope.
  
  
  RESULTS
  APLs (mean+/-SEM) were measured during head-up tilt test in 26 patients who presented with unexplained syncope. In the 15 patients with a negative test, APLs were 0.39+/-0.03 micromol/L at baseline, 0.22+/-0.03 micromol/L immediately after tilting, and 0.44+/-0.03 micromol/L after 45 minutes. APLs were significantly higher in the 11 patients with a positive test (2.66+/-0.67 micromol/L at baseline and 3.22+/-0.85 micromol/L immediately after tilting) than in those with a negative test. During tilt testing-induced syncope, APLs increased to reach 4.03+/-0.66 micromol/L (ie, a 52% increase compared with baseline levels; P<0.02). Furthermore, we observed that the higher the APL during syncope, the shorter the time to appearance of symptoms.
  
  
  CONCLUSIONS
  This study showed that APLs were higher in patients with a positive tilt test than in patients with a negative test and that they increased during tilt testing-induced syncope. These observations suggest that adenosine release may be involved in the triggering mechanism of syncope induced during tilt testing.
authors.affiliation: Division of Cardiology, Centre Hospitalo-Universitaire Nord, Marseille, France.
authors.forename: Alain Y
authors.initials: AY
authors.lastname: Saadjian
authors.forename: Samuel
authors.initials: S
authors.lastname: Lévy
authors.forename: Fréderic
authors.initials: F
authors.lastname: Franceschi
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Zouher
authors.forename: Franck
authors.initials: F
authors.lastname: Paganelli
authors.forename: Régis P
authors.initials: RP
authors.lastname: Guieu
mesh_terms: D000241:Adenosine / Q000097:blood*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001794:Blood Pressure; D003710:Demography; D018450:Disease Progression; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013318:Stroke Volume; D019462:Syncope, Vasovagal / Q000097:blood* / Q000175:diagnosis* / Q000209:etiology; D018667:Tilt-Table Test / Q000009:adverse effects
chemical_list: D000241:Adenosine