Endothelin-1 plasma levels are not elevated in patients with obstructive sleep apnoea

Endothelin-1 (ET-1), a potent vasoconstrictor, is released mainly by vascular endothelial cells under the influence of hypoxia and other stimuli. ET-1 is related to endothelial dysfunction, as well as arterial and pulmonary hypertension, all of which are thought to be associated with obstructive sleep apnoea (OSA). This study evaluated venous plasma concentrations of ET-1 and noradrenaline and 24-h systemic blood pressure in 29 patients with OSA (age=56.9+/-1.6 yrs; body mass index=29.5+/-0.7 kg x m2 (mean+/-SEM)). Blood samples were taken in the morning, evening and during sleep. In the same way, the patients were assessed during a night of continuous positive airway pressure (CPAP) and after 13.9+/-1.4 months while still on CPAP. ET-1 levels were compared to those of control subjects, who were selected from in- and outpatients and were matched to patients for age, sex, presence of arterial hypertension and coronary artery disease. ET-1 plasma levels were not elevated in the patients compared to the controls (41.6+/-2.2 and 44.9+/-1.3 pg x mL(-1), respectively, p=0.20). The ET-1 concentration did not change significantly, neither during sleep nor in the first night on CPAP therapy, nor under long-term treatment with CPAP. ET-1 neither correlated to the severity of OSA nor to that of systemic hypertension. The results suggest that endothelin-1 does not play a crucial role in the pathophysiology of obstructive sleep apnoea.