Overnight hypoxic exposure and glucagon-like peptide-1 and leptin levels in humans

Altitude exposure has been associated with loss of appetite and weight loss in healthy humans; however, the endocrine factors that contribute to these changes remain unclear. Leptin and glucagon-like peptide-1 (GLP-1) are peptide hormones that contribute to the regulation of appetite. Leptin increases with hypoxia; however, the influence of hypoxia on GLP-1 has not been studied in animals or humans to date. We sought to determine the influence of normobaric hypoxia on plasma leptin and GLP-1 levels in 25 healthy humans. Subjects ingested a control meal during normoxia and after 17 h of exposure to normobaric hypoxia (fraction of inspired oxygen of 12.5%, simulating approximately 4100 m). Plasma leptin was assessed before the meal, and GLP-1 was assessed premeal, at 20 min postmeal, and at 40 min postmeal. We found that hypoxia caused a significant elevation in plasma leptin levels (normoxia, 4.9 ± 0.8 pg·mL^-1; hypoxia, 7.7 ± 1.5 pg·mL^-1; p < 0.05; range, -16% to 190%), no change in the average GLP-1 response to hypoxia, and only a small trend toward an increase in GLP-1 levels 40 min postmeal (fasting, 15.7 ± 0.9 vs 15.9 ± 0.7 pmol·L ^-1; 20 min postmeal, 21.7 ± 0.9 vs 21.8 ± 1.2 pmol·L^-1; 40 min postmeal, 19.5 ± 1.2 vs. 21.0 ± 1.2 pmol·L^-1 for normoxia and hypoxia, respectively; p > 0.05 normoxia vs hypoxia). There was a correlation between SaO₂ and leptin after the 17 h exposure (r = 0.45; p < 0.05), but no relation between SaO₂ and GLP-1. These data confirm that leptin increases with hypoxic exposure in humans. Further study is needed to determine the influence of hypoxia and altitude on GLP-1 levels.