title: Enhanced activity of sodium-lithium countertransport in patients with cardiac syndrome X: a potential link between cardiac and metabolic syndrome X.
abstract: OBJECTIVE
  This study was aimed at assessing both stimulated insulinemia and the sodium-lithium countertransport in a selected group of patients with cardiac syndrome X.
  
  
  BACKGROUND
  Hyperinsulinemia, which is frequently present in patients with cardiac syndrome X, is often associated with an enhanced activity of the sodium-lithium countertransport, an in vitro marker of sodium-hydrogen exchange.
  
  
  METHODS
  Fifteen patients with syndrome X and 14 matched controls were studied. After pharmacological washout, sodium-lithium countertransport was assessed from lithium-loaded red blood cells. Postload insulin levels were evaluated by a double-antibody radioimmunoassay.
  
  
  RESULTS
  Maximal velocity of sodium-lithium countertransport was higher in patients with syndrome X compared to controls (635+/-200 vs. 324+/-49 micromol/liter/h, p = 0.001). Fourteen of the 15 patients with syndrome X (93%) presented sodium-lithium countertransport values higher than the mean +2 SD of the control group. At 120 min, 12 patients with syndrome X (80%) had plasma levels of insulin >420 pmol/liter, which corresponds to the mean value +2 SD of controls (p = 0.006).
  
  
  CONCLUSIONS
  Both enhanced activity of the sodium-lithium countertransport and stimulated hyperinsulinemia are present in the vast majority of patients with cardiac syndrome X. As enhanced activity of the sodium-lithium countertransport has the potential to cause both glucose intolerance and smooth muscle hyperreactivity, it might represent a common cause of the metabolic and vascular alterations frequently found in syndrome X.
authors.affiliation: Divisione di Cardiochirurgia, Università Tor Vergata, Rome, Italy. gaspardone@tin.it
authors.forename: A
authors.initials: A
authors.lastname: Gaspardone
authors.forename: C
authors.initials: C
authors.lastname: Ferri
authors.forename: F
authors.initials: F
authors.lastname: Crea
authors.forename: F
authors.initials: F
authors.lastname: Versaci
authors.forename: F
authors.initials: F
authors.lastname: Tomai
authors.forename: A
authors.initials: A
authors.lastname: Santucci
authors.forename: L
authors.initials: L
authors.lastname: Chiariello
authors.forename: P A
authors.initials: PA
authors.lastname: Gioffre
mesh_terms: D001693:Biological Transport, Active; D004912:Erythrocytes / Q000378:metabolism*; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D017136:Ion Transport; D008094:Lithium / Q000378:metabolism*; D008297:Male; D017566:Microvascular Angina / Q000097:blood* / Q000503:physiopathology; D008875:Middle Aged; D011863:Radioimmunoassay; D012964:Sodium / Q000378:metabolism*
chemical_list: D007328:Insulin; D008094:Lithium; D012964:Sodium