title: Endocrine responses to acute and chronic high-altitude exposure (4,300 meters): modulating effects of caloric restriction.
abstract: High-altitude anorexia leads to a hormonal response pattern modulated by both hypoxia and caloric restriction (CR). The purpose of this study was to compare altitude-induced neuroendocrine changes with or without energy imbalance and to explore how energy sufficiency alters the endocrine acclimatization process. Twenty-six normal-weight, young men were studied for 3 wk. One group [hypocaloric group (HYPO), n = 9] stayed at sea level and consumed 40% fewer calories than required to maintain body weight. Two other groups were deployed to 4,300 meters (Pikes Peak, CO), where one group (ADQ, n = 7) was adequately fed to maintain body weight and the other [deficient group (DEF), n = 10] had calories restricted as above. HYPO experienced a typical CR-induced reduction in many hormones such as insulin, testosterone, and leptin. At altitude, fasting glucose, insulin, and epinephrine exhibited a muted rise in DEF compared with ADQ. Free thyroxine, thyroid-stimulating hormone, and norepinephrine showed similar patterns between the two altitude groups. Morning cortisol initially rose higher in DEF than ADQ at 4,300 meters, but the difference disappeared by day 5. Testosterone increased in both altitude groups acutely but declined over time in DEF only. Adiponectin and leptin did not change significantly from sea level baseline values in either altitude group regardless of energy intake. These data suggest that hypoxia tends to increase blood hormone concentrations, but anorexia suppresses elements of the endocrine response. Such suppression results in the preservation of energy stores but may sacrifice the facilitation of oxygen delivery and the use of oxygen-efficient fuels.
authors.affiliation: Clinical Studies Unit, VA Palo Alto Health Care System, 3801 Miranda Ave., Palo Alto, CA 94304, USA.
authors.forename: Kimberly E
authors.initials: KE
authors.lastname: Barnholt
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Hoffman
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rock
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Muza
authors.forename: Charles S
authors.initials: CS
authors.lastname: Fulco
authors.forename: Barry
authors.initials: B
authors.lastname: Braun
authors.forename: Leah
authors.initials: L
authors.lastname: Holloway
authors.forename: Robert S
authors.initials: RS
authors.lastname: Mazzeo
authors.forename: Allen
authors.initials: A
authors.lastname: Cymerman
authors.forename: Anne L
authors.initials: AL
authors.lastname: Friedlander
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000531:Altitude; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D031204:Caloric Restriction; D004038:Diet, Reducing / Q000009:adverse effects; D004734:Energy Metabolism; D006706:Homeostasis; D006728:Hormones / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology; D008297:Male; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D006728:Hormones; D007328:Insulin