Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 120, Issue 8, Pages 947-955Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00897.2015
Keywords
normobaric hypoxia; simulated microgravity; insulin sensitivity; cholesterol
Categories
Funding
- European Union Programme FP7 (PlanHab project) [284438]
- European Space Agency (ESA) Programme for European Cooperating States (ESTEC) [40001043721/11/NL/KML]
- Slovene Research Agency [L3-3654]
- MRC/ARUK Centre for Musculoskeletal Ageing Research [MR/K00414X/1, 19891 2012 -2017]
- MRC [MR/K00414X/1] Funding Source: UKRI
- Medical Research Council [MR/K00414X/1] Funding Source: researchfish
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PlanHab is a planetary habitat simulation study. The atmosphere within future space habitats is anticipated to have reduced PO2, but information is scarce as to how physiological systems may respond to combined exposure to moderate hypoxia and reduced gravity. This study investigated, using a randomized-crossover design, how insulin sensitivity, glucose tolerance, and circulating lipids were affected by 16 days of horizontal bed rest in normobaric normoxia [NBR: FIO2 = 0.209; PIO2 = 133.1 (0.3) mmHg], horizontal bed rest in normobaric hypoxia [HBR: FIO2 = 0.141 (0.004); PIO2 = 90.0 (0.4) mmHg], and confinement in normobaric hypoxia combined with daily moderate intensity exercise (HAMB). A mixed-meal tolerance test, with arterialized-venous blood sampling, was performed in 11 healthy, nonobese men (25-45 yr) before (V1) and on the morning of day 17 of each intervention (V2). Postprandial glucose and c-peptide response were increased at V2 of both bed rest interventions (P < 0.05 in each case), with c-peptide: insulin ratio higher at V2 in HAMB and HBR, both in the fed and fasted state (P < 0.005 in each case). Fasting total cholesterol was reduced at V2 in HAMB [-0.47 (0.36) mmol/l; P < 0.005] and HBR [-0.55 (0.41) mmol/l; P < 0.005]. Fasting HDL was lower at V2 in all interventions, with the reduction observed in HBR [-0.30 (0.21) mmol/l] greater than that measured in HAMB [-0.13 (0.14) mmol/l; P < 0.005] and NBR [-0.17 (0.15) mmol/l; P < 0.05]. Hypoxia did not alter the adverse effects of bed rest on insulin sensitivity and glucose tolerance but appeared to increase insulin clearance. The negative effect of bed rest on HDL was compounded in hypoxia, which may have implications for long-term health of those living in future space habitats.
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