Role of Sodium-Hydrogen Exchanger-1 (NHE-1) in the Effect of Exercise on Intermittent Hypoxia-Induced Left Ventricular Dysfunction.

Intermittent hypoxia (IH) occurs frequently in patients with obstructive sleep apnoea and can cause ventricular dysfunction. However, whether myocardial inflammation and sodium-hydrogen exchanger-1 (NHE-1) expression play an important role in IH-induced ventricular dysfunction remains unclear. This study aimed to investigate whether short-term exercise provides a protective effect on IH-induced left ventricular (LV) function impairment. Male Sprague-Dawley rats were randomly assigned to 4 groups: control (CON), IH, exercise (EXE) or IH interspersed with EXE (IHEXE). IH rats were exposed to repetitive hypoxia/reoxygenation cycles (2%-6% O₂ for 2-5 s per 75 s, followed by 21% O₂ for 6 h/day) during the light phase for 12 consecutive days. EXE rats were habituated to treadmill running for 5 days, permitted 2 days of rest, and followed by 5 exercise bouts (30 m/min for 60 min on a 2% grade) on consecutive days during the dark phase. IHEXE rats were exposed to IH during the light phase interspersed with exercise programs during the dark phase on the same day. Cardiac function was quantified by echocardiographic evaluation. Myocardial levels of tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and NHE-1 were determined. IH rats showed LV dysfunction characterized by lower LV fractional shortening (LVFS%) and LV ejection fraction (LVEF%). LV dysfunction was associated with higher myocardial levels of TNF-α, IL-6 and NHE-1 mRNA and protein. These changes were not observed in IHEXE rats (P > 0.05 for all). EXE rats showed lower levels of NHE-1 protein than CON rats (P < 0.05). However, the levels of LVFS%, LVEF%, TNF-α and IL-6 protein and NHE-1 mRNA did not differ between EXE and CON rats (P > 0.05 for all). These data indicated that exercise may provide a protective effect on IH-induced LV dysfunction by attenuating IH-induced myocardial NHE-1 hyperactivity.