Plasma apelin levels in obstructive sleep apnea and the effect of continuous positive airway pressure therapy

Apelin is a peptide hormone with cardiovascular and glucose homeostasis properties, and obstructive sleep apnea (OSA) is complicated by cardiovascular and metabolic comorbidities. Plasma apelin has not been previously assessed in OSA. We investigated the response of plasma apelin to a 2-h 75 g oral glucose tolerance test (OGTT) and the effect of 3 months compliant continuous positive airway pressure (CPAP) therapy in 15 obese males with newly diagnosed OSA. Plasma apelin and serum cortisol were recorded 10 minutely, while serum insulin and glucose were measured 30 minutely. Ten subjects had plasma apelin measured at intervals across a 24-h period to investigate for circadian variation in apelin levels, and this was repeated following 3 months compliant CPAP therapy. Fasting (0.342±0.038 vs 0.288±0.024 ng/ml, P=0.04), 30 min (0.399±0.035 vs 0.312±0.036 ng/ml, P=0.007) and 120 min (0.402±0.030 vs 0.259±0.024 ng/ml, P