Enhanced activity of sodium-lithium countertransport in patients with cardiac syndrome X: a potential link between cardiac and metabolic syndrome X.
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.
Gaspardone
A
A
Divisione di Cardiochirurgia, Università Tor Vergata, Rome, Italy. gaspardone@tin.it
Ferri
C
C
Crea
F
F
Versaci
F
F
Tomai
F
F
Santucci
A
A
Chiariello
L
L
Gioffre
P A
PA
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*
D007328:Insulin; D008094:Lithium; D012964:Sodium