Increased expression of adenosine A2A receptors in patients with spontaneous and head-up-tilt-induced syncope

Heart Rhythm. 2007 Jul;4(7):870-6. doi: 10.1016/j.hrthm.2007.03.002. Epub 2007 Mar 12.

Abstract

Background: Adenosine may play a role in the triggering of neurocardiogenic syncope, but no information on adenosine receptors is available at the present time.

Objective: The purpose of this study was to investigate whether adenosine A2A receptors expression is altered in patients with neurocardiogenic syncope.

Methods: Adenosine plasma levels (APLs), the expression of A2A receptors, were measured (mean +/- standard error of the mean) during tilt testing. Expression of receptors was assessed on mononuclear cells using a selective receptor ligand.

Results: At baseline, the APLs of 16 patients with a positive test were higher than those of 17 patients with a negative test and of those of a control group (2.10 +/- 0.30 vs. 0.40 +/- 0.05 and 0.41 +/- 0.06 muM, respectively; P <.0001). The number of receptors was higher in patients tested positive than in patients tested negative or in the control group (122 +/- 10 vs. 38 +/- 4 and 44 +/- 4 fmol/g of proteins, respectively; P <.0001). No difference was found in the affinity or synthesis among the three groups.

Conclusion: This study showed an increased number and an up-regulation of adenosine A2A receptors in patients with spontaneous syncope and a positive head-up tilt, which in the context of high APLs may play a role in the recurrence of syncopal episodes.

MeSH terms

  • Adenosine / metabolism
  • Adolescent
  • Adult
  • Aged
  • Case-Control Studies
  • Female
  • Gene Expression Regulation*
  • Humans
  • Male
  • Middle Aged
  • Receptor, Adenosine A2A / genetics
  • Receptor, Adenosine A2A / metabolism*
  • Syncope / blood
  • Syncope / etiology*
  • Syncope / metabolism*

Substances

  • Receptor, Adenosine A2A
  • Adenosine