Elevated plasma cholecystokinin at high altitude: metabolic implications for the anorexia of acute mountain sickness

Antagonizing cholecystokinin A receptor in the lung attenuates obesity-induced airway hyperresponsiveness

Obesity increases asthma prevalence and severity. However, the underlying mechanisms are poorly understood, and consequently, therapeutic options for asthma patients with obesity remain limited. Here we report that cholecystokinin-a metabolic hormone best known for its role in signaling satiation and fat metabolism-is increased in the lungs of obese mice and that pharmacological blockade of cholecystokinin A receptor signaling reduces obesity-associated airway hyperresponsiveness. Activation of cholecystokinin A receptor by the hormone induces contraction of airway smooth muscle cells. In vivo, cholecystokinin level is elevated in the lungs of both genetically and diet-induced obese mice. Importantly, intranasal administration of cholecystokinin A receptor antagonists (proglumide and devazepide) suppresses the airway hyperresponsiveness in the obese mice. Together, our results reveal an unexpected role for cholecystokinin in the lung and support the repurposing of cholecystokinin A receptor antagonists as a potential therapy for asthma patients with obesity.

Effects of Three Different Modes of Resistance Training on Appetite Hormones in Males With Obesity

Purpose

This study explored the effect of three different modes of resistance training on appetite hormones [leptin, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine–tyrosine (PYY)], cardiometabolic and anthropometric measures in males with obesity.

Methods

Forty-four males with obesity (age: 27.5 ± 9.4 yrs.; mean weight: 93.2 ± 2.2 kg, body mass index: 32.9 ± 1.2 kg/m²) were randomized to traditional resistance training (TRT, n = 11), circuit resistance training (CRT, n = 11), interval resistance training (IRT, n = 11) or control (C, n = 11) groups. All resistance training groups received 50 min of supervised training per session, three days per week, for 12 weeks. Measurements were taken at baseline and after 12 weeks of training.

Results

Plasma levels of leptin, ghrelin, CCK, and PYY decreased significantly in all three different modalities of resistance training groups when compared to the control group (p < 0.05). GLP-1 increased significantly in both CRT and IRT groups compared to TRT and C groups (p < 0.05). Glucose-dependent insulinotropic polypeptide decreased significantly in CRT and IRT groups compared to the C group (p < 0.05). Adiponectin levels increased significantly in all resistance training groups compared to the C group (p < 0.05).

Conclusion

Overall, CRT and IRT protocols had the greatest impact on appetite hormones compared to individuals who engaged in TRT or did not exercise (C).

Effect of high altitude on human postprandial 13 C-octanoate metabolism, intermediary metabolites, gastrointestinal peptides, and visceral perception

OBJECTIVE

At high altitude (HA), acute mountain sickness (AMS) is accompanied by neurologic and upper gastrointestinal symptoms (UGS). The primary aim of this study was to test the hypothesis that delayed gastric emptying (GE), assessed by ¹³ C-octanoate breath testing (OBT), causes UGS in AMS. The secondary aim was to assess post-gastric mechanisms of OBT, which could confound results under these conditions, by determination of intermediary metabolites, gastrointestinal peptides, and basal metabolic rate.

METHODS

A prospective trial was performed in 25 healthy participants (15 male) at 4559 m (HA) and at 490 m (Zurich). GE was assessed by OBT (428 kcal solid meal) and UGS by visual analogue scales (VAS). Blood sampling of metabolites (glucose, free fatty acids (FFA), triglycerides (TG), beta-hydroxyl butyrate (BHB), L-lactate) and gastrointestinal peptides (insulin, amylin, PYY, etc.) was performed as well as blood gas analysis and spirometry.

STATISTICAL ANALYSIS

variance analyses, bivariate correlation, and multilinear regression analysis.

RESULTS

After 24 h under hypoxic conditions at HA, participants developed AMS (p < 0.001). ¹³ CO₂ exhalation kinetics increased (p < 0.05) resulting in reduced estimates of gastric half-emptying times (p < 0.01). However, median resting respiratory quotients and plasma profiles of TG indicated that augmented beta-oxidation was the main predictor of accelerated ¹³ CO₂ -generation under these conditions.

CONCLUSION

Quantification of ¹³ C-octanoate oxidation by a breath test is sensitive to variation in metabolic (liver) function under hypoxic conditions. ¹³ C-breath testing using short-chain fatty acids is not reliable for measurement of gastric function at HA and should be considered critically in other severe hypoxic conditions, like sepsis or chronic lung disease.

Comparison of effects in sustained and diel-cycling hypoxia on hypoxia tolerance, histology, physiology and expression of clock genes in high latitude fish Phoxinus lagowskii

Phoxinus lagowskii is a popular fish in Chinese cuisine. Though it is found mainly in China's high-latitude regions, where diel-cycling hypoxia (DCH) is known to have unique impacts on aquatic organisms, there is little known about its response to hypoxia. Currently, nothing is known about the changes in blood parameters, gill and liver morphology, glucose and lipid metabolism, or expression of genes involved in clock and glucose metabolism in response to sustained hypoxia (SH) and diel-cycling hypoxia (DCH). To elucidate the influence of sustained and diel-cycling hypoxia on fish hypoxia tolerance, resting oxygen consumption (MO₂) analysis was performed after ten days of hypoxia. This analysis revealed that hypoxia tolerance profoundly improved after ten days of either sustained or diel-cycling hypoxia acclimation, with DCH groups showing greater improvements than SH groups. Additionally, an increase in RBCs was found in P. lagowskii, suggesting an increase in the O₂-carrying capacity of the blood to tolerate hypoxia. Hemoglobin (Hb) concentrations in P. lagowskii were increased at four days of diel-cycling hypoxia, confirming that physiological and metabolic adaptation to hypoxia is based on the duration of O₂ exposure. Increased Hb and hematocrit (Hct) were found in DCH-exposed fish, both of which have been directly linked to high-latitude hypoxia tolerance. In the gills, lamella surface area increased in SH-exposed fish more than DCH-exposed fish, and these increases were accompanied by a decrease in the volume of interlamellar cell mass (ILCM). Histology changes in the liver showed a higher frequency of cytoplasmic vacuolization in DCH-exposed fish. PK increases in SH-exposed fish suggest that fish can use more energy sources in persistent hypoxia. Meanwhile, DCH-exposed fish use TG as an energy source. In SH-exposed fish, self-regulation of Cry1a was observed, whereas Cry1b gene was up-regulated significantly. In DCH-exposed fish, three of eight clock genes studied had increased expression, including Per1a, Clocka, and Cry1b, suggesting that SH and DCH result in different hypoxic responses. This study presents a novel approach to the study of fish responses to hypoxia in high latitude and shows that sustained hypoxia and diel-cycling hypoxia induce large differences in fish physiology.

Hypoxia transactivates cholecystokinin gene expression in 3D-engineered muscle

At high altitudes, the hypoxic atmosphere decreases the oxygen partial pressure in the body, inducing several metabolic changes in tissues and cells. Furthermore, it exerts potent anorectic effects, thus causing an energy deficit. Two decades ago, a marked increase in the resting level of plasma cholecystokinin (CCK) was observed in humans at the Mt. Kanchenjunga basecamp, located at 5100 m above the sea level, compared to sea-level control values. Interestingly, acute exercise also raises plasma CCK and exerts potent anorectic effects under normoxic conditions. However, the transcriptional regulations of Cck gene underlying these effects have not yet been established. Here, we employed acute electrical pulse stimulation (EPS) followed by microarray analysis to discover novel myokines in 3D-engineered muscle. Acute EPS affects the contractile function, inducing a decline in the contractile force. Surprisingly, microarray analysis revealed an EPS-induced activation of cholecystokinin receptor (CCKR)-mediated signaling. Furthermore, Cck was constitutively upregulated in 3D-engineered muscle, and its expression increased under hypoxic conditions. Notably, a hypoxia-responsive element was detected in the Cck promoters of mice and humans. Our results suggested that hypoxia transactivated Cck expression in 3D-engineered muscle. Furthermore, the elevation in plasma CCK levels following acute exercise or at high altitude might be partly attributed to myogenic cells.

The hypoxia response and nutritional peptides

Hypoxia controls metabolism at several levels, e.g., via mitochondrial ATP production, glucose uptake and glycolysis. Hence it is likely that hypoxia also affects the action and/or production of many peptide hormones linked to food intake and appetite control. Many of those are produced in the gastrointestinal tract, endocrine pancreas, adipose tissue, and selective areas in the brain which modulate and concert their actions. However, the complexity of the hypoxia response and the links to peptides/hormones involved in food intake and appetite control in the different organs are not well known. This review summarizes the role of the hypoxia response and its effects on major peptides linked to appetite regulation, nutrition and metabolism.

The impact of functional food on the prevention and treatment of respiratory diseases

Globally, diseases of the lung are one of the main causes of death, and conventional therapies are often ineffective in dealing with this serious medical and sociological problem. Since ancient times, medicinal plants have been used in the treatment of respiratory tract diseases. Such plants show antitussive, muscle relaxing, bronchi dilation or cillary movement effects. Their usefulness has been confirmed by modern and current research. A medicinal plant that is also a functional food can open new areas in the prevention and treatment of respiratory tract diseases. In this review, information about the influence of functional food on preventing and treating asthma, chronic obstructive pulmonary disorder (COPD) and high-altitude sickness are presented.

Appetite Suppression and Altered Food Preferences Coincide with Changes in Appetite-Mediating Hormones During Energy Deficit at High Altitude, But Are Not Affected by Protein Intake

Karl, J. Philip, Renee E. Cole, Claire E. Berryman, Graham Finlayson, Patrick N. Radcliffe, Matthew T. Kominsky, Nancy E. Murphy, John W. Carbone, Jennifer C. Rood, Andrew J. Young, and Stefan M. Pasiakos. Appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at high altitude, but are not affected by protein intake. High Alt Med Biol. 19:156-169, 2018.-Anorexia and unintentional body weight loss are common during high altitude (HA) sojourn, but underlying mechanisms are not fully characterized, and the impact of dietary macronutrient composition on appetite regulation at HA is unknown. This study aimed to determine the effects of a hypocaloric higher protein diet on perceived appetite and food preferences during HA sojourn and to examine longitudinal changes in perceived appetite, appetite mediating hormones, and food preferences during acclimatization and weight loss at HA. Following a 21-day level (SL) period, 17 unacclimatized males ascended to and resided at HA (4300 m) for 22 days. At HA, participants were randomized to consume measured standard-protein (1.0 g protein/kg/d) or higher protein (2.0 g/kg/d) hypocaloric diets (45% carbohydrate, 30% energy restriction) and engaged in prescribed physical activity to induce an estimated 40% energy deficit. Appetite, food preferences, and appetite-mediating hormones were measured at SL and at the beginning and end of HA. Diet composition had no effect on any outcome. Relative to SL, appetite was lower during acute HA (days 0 and 1), but not different after acclimatization and weight loss (HA day 18), and food preferences indicated an increased preference for sweet- and low-protein foods during acute HA, but for high-fat foods after acclimatization and weight loss. Insulin, leptin, and cholecystokinin concentrations were elevated during acute HA, but not after acclimatization and weight loss, whereas acylated ghrelin concentrations were suppressed throughout HA. Findings suggest that appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at HA. Although dietary protein intake did not impact appetite, the possible incongruence with food preferences at HA warrants consideration when developing nutritional strategies for HA sojourn.

A Systematic Review and Meta-Analysis Reveals Altered Drug Pharmacokinetics in Humans During Acute Exposure to Terrestrial High Altitude-Clinical Justification for Dose Adjustment?

Bailey, Damian Miles, Benjamin S. Stacey, and Mark Gumbleton. A systematic review and meta-analysis reveals altered drug pharmacokinetics in humans during acute exposure to terrestrial high altitude-clinical justification for dose adjustment? High Alt Med Biol. 19:141-148, 2018.

OBJECTIVE

While physiological responses during acute ascent to terrestrial high altitude (HA) have the potential to alter the pharmacokinetics (PKs) that define absorption and disposition of medicinal drugs, there have been no systematic reviews and meta-analyses performed to date.

METHODS

We conducted a systematic literature search in June 2017 using NCBI PubMed, EMBASE, Web of Science, and Ovid MEDLINE databases to identify relevant observational studies. Studies were deemed eligible based on the following criteria: (1) participants: healthy, nonacclimatized male or female lowlanders (born and bred at sea level) and (2) environment: exposure to low altitude (LA, ≤600 m), followed by terrestrial high altitude (HA, ≤24 hours to ≥2500 m), the time course specifically selected to avoid interpretive complications associated with erythrocytosis. All PK parameters were standardized to be in the same units and the weighted standardized mean difference (SMD) calculated using a combination of fixed and random effects models with heterogeneity evaluated using χ² and I² statistics.

RESULTS

Of 20,840 studies reviewed, 6 prospective cohort studies (n = 75) qualified for inclusion, with participants exposed to a mean altitude of 4025 (mean) ± 380 (SD) m. We observed increases for absorption half-life (SMD: 0.40, 95% CI: 0.01-0.80, p = 0.04], elimination half-life (SMD: 0.89, 95% CI: 0.30-1.48, p = 0.003), and erythrocyte binding (SMD: 0.52, 95% CI: 0.16-0.88, p = 0.004) and reduction in clearance (SMD: -0.56, 95% CI: -1.13 to 0.00, p = 0.05).

CONCLUSIONS

Collectively, these findings reveal impairments in both oral absorption and corresponding clearance of the, although limited, sample of drugs at HA that may potentially require closer patient monitoring and dose adjustments to maintain therapeutic efficacy and avoid incidental toxicity.

"Living High-Training Low" improved weight loss and glucagon-like peptide-1 level in a 4-week weight loss program in adolescents with obesity: A pilot study

BACKGROUND

"Living High-Training Low" (LHTL) is effective for the improvement of athletic ability; however, little is known about the effect of LHTL on obese individuals. The present study determined whether LHTL would have favorable influence on body composition, rebalance the appetite hormones, and explore the underlying mechanism.

METHODS

Adolescents with obesity [body mass index (BMI) >30 kg/m] were randomly assigned to "Living Low-Training Low" (LLTL, n = 19) group that slept in a normobaric normoxia condition and the LHTL (n = 16) group slept in a normobaric hypoxia room (14.7% PO2 ∼2700 m). Both groups underwent the same aerobic exercise training program. Morphological, blood lipids, and appetite hormones were measured and assessed.

RESULTS

After the intervention, the body composition improved in both groups, whereas reductions in body weight (BW), BMI, and lean body mass increased significantly in the LHTL group (all, P < .05). In the LLTL group, cholecystokinin (CCK) decreased remarkably (P < .05) and CCK changes were positively associated with changes in BW (r = 0.585, P = .011) and BMI (r = 0.587, P = .010). However, in the LHTL group, changes in plasma glucagon-like peptide-1 (GLP-1) and interleukin-6 (IL-6) levels, positively correlated with each other (r = 0.708, P = .015) but negatively with BW changes (r = -0.608, P = .027 and r = -0.518, P = .048, respectively).

CONCLUSION

The results indicated that LHTL could induce more weight loss safely and efficiently as compared to LLTL and increase the plasma GLP-1 levels that may be mediated by IL-6 to rebalance the appetite. Thus, an efficient method to treat obesity and prevent weight regain by appetite rebalance in hypoxia condition was established.

Hypoxia-Related Hormonal Appetite Modulation in Humans during Rest and Exercise: Mini Review

Obesity is associated with numerous chronic ailments and represents one of the major health and economic issues in the modernized societies. Accordingly, there is an obvious need for novel treatment approaches. Recently, based on the reports of reduced appetite and subsequent weight loss following high-altitude sojourns, exposure to hypoxia has been proposed as a viable weight-reduction strategy. While altitude-related appetite modulation is complex and not entirely clear, hypoxia-induced alterations in hormonal appetite modulation might be among the key underlying mechanisms. The present paper summarizes the up-to-date research on hypoxia/altitude-induced changes in the gut and adipose tissue derived peptides related to appetite regulation. Orexigenic hormone ghrelin and anorexigenic peptides leptin, glucagon-like peptide-1, peptide YY, and cholecystokinin have to-date been investigated as potential modulators of hypoxia-driven appetite alterations. Current evidence suggests that hypoxia can, especially acutely, lead to decreased appetite, most probably via reduction of acylated ghrelin concentration. Hypoxia-related short and long-term changes in other hormonal markers are more unclear although hypoxia seems to importantly modulate leptin levels, especially following prolonged hypoxic exposures. Limited evidence also suggests that different activity levels during exposures to hypoxia do not additively affect hormonal appetite markers. Although very few studies have been performed in obese/overweight individuals, the available data indicate that hypoxia/altitude exposures do not seem to differentially affect appetite regulation via hormonal pathways in this cohort. Given the lack of experimental data, future well-controlled acute and prolonged studies are warranted to expand our understanding of hypoxia-induced hormonal appetite modulation and its kinetics in health and disease.

Living at Higher Altitude and Incidence of Overweight/Obesity: Prospective Analysis of the SUN Cohort

BACKGROUND

Residence at high altitude has been associated with lower obesity rates probably due to hypoxia conditions. However, there is no evidence of this association in a free-living population.

OBJECTIVES

We assessed the association between the altitude where each participant of a Spanish cohort (the SUN Project) was living and the incidence of overweight/obesity.

METHODS

The SUN Project is a dynamic, prospective, multipurpose cohort of Spanish university graduates with a retention rate of 89%. We included in the analysis 9 365 participants free of overweight/obesity at baseline. At the baseline questionnaire, participants reported their postal code and the time they had been living in their city/village. We imputed the altitude of each postal code according to the data of the Spanish National Cartographic Institute and categorized participants in tertiles. We used Cox regression models to adjust for potential confounding variables.

RESULTS

During a median follow-up of 10 years, we identified 2 156 incident cases of overweight/obesity. After adjusting for sex, age, time of residence at current city, baseline body mass index, physical activity, sedentarism and years of education (≤ 3 years, ≥ 4 years, Master/PhD), those participants in the third tertile (>456 m) exhibited a statistically significant 14% reduction in the risk of developing overweight/obesity in comparison to those in the first tertile (<124 m) (adjusted HR = 0.86; 95% CI: 0.77, 0.96).

CONCLUSIONS

Living in cities of higher altitude was inversely associated with the risk of developing overweight/obesity in a cohort of Spanish university graduates.

Brain Food at High Altitude

Scenic view at high altitude is a pleasure to the eyes, but it has some shortcoming effects as well. High altitude can be divided into different categories, i.e., high altitude (3000-5000 ft), very high altitude (5000-8000 ft), and extreme altitude (above 8000 ft). Much of the population resides at high altitude, and others go there for tourism. Military personnel are also posted there to defend boundaries. As we ascent to high altitude, partial pressure of oxygen reduces, whereas concentration remains the same; this reduces the availability of oxygen to different body parts. This pathophysiological condition is known as hypobaric hypoxia (HH) which leads to oxidative stress and further causes cognitive dysfunction in some cases. Hypoxia causes neurodegeneration in different brain regions; however, the hippocampus is found to be more prone in comparison to other brain regions. As the hippocampus is affected most, therefore, spatial memory is impaired most during such condition. This chapter will give a brief review of the damaging effect of high altitude on cognition and also throw light on possible herbal interventions at high altitude, which can improve cognitive performance as well as provide protection against the deteriorating effect of hypobaric hypoxia at high altitude.

Altitude training for elite endurance athletes: A review for the travel medicine practitioner

High altitude training is regarded as an integral component of modern athletic preparation, especially for endurance sports such as middle and long distance running. It has rapidly achieved popularity among elite endurance athletes and their coaches. Increased hypoxic stress at altitude facilitates key physiological adaptations within the athlete, which in turn may lead to improvements in sea-level athletic performance. Despite much research in this area to date, the exact mechanisms which underlie such improvements remain to be fully elucidated. This review describes the current understanding of physiological adaptation to high altitude training and its implications for athletic performance. It also discusses the rationale and main effects of different training models currently employed to maximise performance. Athletes who travel to altitude for training purposes are at risk of suffering the detrimental effects of altitude. Altitude illness, weight loss, immune suppression and sleep disturbance may serve to limit athletic performance. This review provides an overview of potential problems which an athlete may experience at altitude, and offers specific training recommendations so that these detrimental effects are minimised.

How wasting is saving: weight loss at altitude might result from an evolutionary adaptation

At extreme altitude (>5,000 – 5,500 m), sustained hypoxia threatens human function and survival, and is associated with marked involuntary weight loss (cachexia). This seems to be a coordinated response: appetite and protein synthesis are suppressed, and muscle catabolism promoted. We hypothesise that, rather than simply being pathophysiological dysregulation, this cachexia is protective. Ketone bodies, synthesised during relative starvation, protect tissues such as the brain from reduced oxygen availability by mechanisms including the reduced generation of reactive oxygen species, improved mitochondrial efficiency and activation of the ATP-sensitive potassium (K_ATP) channel. Amino acids released from skeletal muscle also protect cells from hypoxia, and may interact synergistically with ketones to offer added protection. We thus propose that weight loss in hypoxia is an adaptive response: the amino acids and ketone bodies made available act not only as metabolic substrates, but as metabolic modulators, protecting cells from the hypoxic challenge.

Lower obesity rate during residence at high altitude among a military population with frequent migration: a quasi experimental model for investigating spatial causation

We sought to evaluate whether residence at high altitude is associated with the development of obesity among those at increased risk of becoming obese. Obesity, a leading global health priority, is often refractory to care. A potentially novel intervention is hypoxia, which has demonstrated positive long-term metabolic effects in rats. Whether or not high altitude residence confers benefit in humans, however, remains unknown. Using a quasi-experimental, retrospective study design, we observed all outpatient medical encounters for overweight active component enlisted service members in the U.S. Army or Air Force from January 2006 to December 2012 who were stationed in the United States. We compared high altitude (>1.96 kilometers above sea level) duty assignment with low altitude (<0.98 kilometers). The outcome of interest was obesity related ICD-9 codes (278.00-01, V85.3x-V85.54) by Cox regression. We found service members had a lower hazard ratio (HR) of incident obesity diagnosis if stationed at high altitude as compared to low altitude (HR 0.59, 95% confidence interval [CI] 0.54–0.65; p<0.001). Using geographic distribution of obesity prevalence among civilians throughout the U.S. as a covariate (as measured by the Centers for Disease Control and Prevention and the REGARDS study) also predicted obesity onset among service members. In conclusion, high altitude residence predicts lower rates of new obesity diagnoses among overweight service members in the U.S. Army and Air Force. Future studies should assign exposure using randomization, clarify the mechanism(s) of this relationship, and assess the net balance of harms and benefits of high altitude on obesity prevention.

Hypoxia, energy balance and obesity: from pathophysiological mechanisms to new treatment strategies

High altitude exposure is often accompanied by weight loss. Postulated mechanisms are a reduction of nutritional energy intake, a reduction of intestinal energy uptake from impaired intestinal function and increased energy expenditure. Beyond the field of altitude, there are good reasons for renewed interest in the relationship between hypoxia and energy balance. The increasing prevalence of obesity and associated comorbidities represent a major health concern. Obesity is frequently associated with sleep disorders leading to intermittent systemic hypoxia with deleterious cardiovascular and metabolic consequences. Hypoxic regions may be present within hypertrophic white adipose tissue leading to chronic systemic inflammation. Among the increasing number of people commuting to altitude for work or leisure, obesity is a risk factor for acute mountain sickness. Paradoxically, exposure to intermittent hypoxia might be considered as a means to lose body mass and to improve metabolic risk factors. Daytime exposure to intermittent hypoxia has been used to treat hypertension in former Soviet Union countries and is now being experimented elsewhere. Such intermittent hypoxic exposure at rest or during exercise may lead to improvement in body composition and health status with improved exercise tolerance, metabolism and systemic arterial pressure. Future research should confirm whether hypoxic training could be a new treatment strategy for weight loss and comorbidities in obese subjects and elucidate the underlying mechanisms and signalling pathways.

Influence of acute exposure to high altitude on basal and postprandial plasma levels of gastroenteropancreatic peptides

Acute mountain sickness (AMS) is characterized by headache often accompanied by gastrointestinal complaints that vary from anorexia through nausea to vomiting. The aim of this study was to investigate the influence of high altitude on plasma levels of gastroenteropancreatic (GEP) peptides and their association to AMS symptoms. Plasma levels of 6 GEP peptides were measured by radioimmunoassay in 11 subjects at 490 m (Munich, Germany) and, after rapid passive ascent to 3454 m (Jungfraujoch, Switzerland), over the course of three days. In a second study (n = 5), the same peptides and ghrelin were measured in subjects who consumed standardized liquid meals at these two elevations. AMS symptoms and oxygen saturation were monitored. In the first study, both fasting (morning 8 a.m.) and stimulated (evening 8 p.m.) plasma levels of pancreatic polypeptide (PP) and cholecystokinin (CCK) were significantly lower at high altitude as compared to baseline, whereas gastrin and motilin concentrations were significantly increased. Fasting plasma neurotensin was significantly enhanced whereas stimulated levels were reduced. Both fasting and stimulated plasma motilin levels correlated with gastrointestinal symptom severity (r = 0.294, p = 0.05, and r = 0.41, p = 0.006, respectively). Mean O(2)-saturation dropped from 96% to 88% at high altitude. In the second study, meal-stimulated integrated (= area under curve) plasma CCK, PP, and neurotensin values were significantly suppressed at high altitude, whereas integrated levels of gastrin were increased and integrated VIP and ghrelin levels were unchanged. In summary, our data show that acute exposure to a hypobaric hypoxic environment causes significant changes in fasting and stimulated plasma levels of GEP peptides over consecutive days and after a standardized meal. The changes of peptide levels were not uniform. Based on the inhibition of PP and neurotensin release a reduction of the cholinergic tone can be postulated.

Plasma adipokine and hormone changes in mountaineers on ascent to 5300 meters

OBJECTIVE

The current study evaluated multiple metabolic and inflammatory hormone responses in recreational climbers (7 men and 3 women, age 26-49 years) over 9 days. In particular, acylation-stimulating protein (ASP), which influences fat storage in adipose tissue, has not been measured at high altitude.

METHODS

Serial measurements were taken at sea level (SL), or 353 m, on day 0, 4000 m on day 3, 4750 m on day 6, and 5300 m on day 9 of the expedition.

RESULTS

Body mass index (BMI) decreased upon ascent to 5300 m from SL (SL 23.2 ± 1.5 kg/m(2); 4000 m 23.2 ± 1.4 kg/m(2); 4750 m 22.9 ± 1.3 kg/m(2); 5300 m 22.3 ± 1.2 kg/m(2); P<.001). Similarly, plasma non-esterified fatty acids and triglycerides increased, while HDL cholesterol decreased (P<.05 to <.001) from SL to 5300 m. Acylation-stimulating protein (SL 42.2 ± 40.2 nm; 4000 m 117.0 ± 69.6 nm; 4750 m 107.9 ± 44.5 nm; 5300 m 82.2 ± 20.2 nm; P=.019) and adiponectin (SL 10.4 ± 6.5 ng/mL, 4000 m 13.9 ± 8.5 ng/mL, 4750 m 18.3 ± 8.3 ng/mL, 5300 m 14.7 ± 8.0 ng/mL; P=.015) increased, as did insulin and Interleukin-6 (IL-6) levels (up to 71% and 168%, respectively; P<.05) with no change in leptin, complement C3 (C3), high sensitivity C-reactive protein (hsCRP) or cortisol levels throughout the mountain ascent from SL to 5300 m.

CONCLUSION

Acylation-stimulating protein and adiponectin are increased during a 9-day period of high altitude (SL to 5300 m) exposure despite weight loss in healthy mountaineers.

Do changes in gastro-intestinal blood flow explain high-altitude anorexia?

BACKGROUND

Gastrointestinal symptoms are common on acute exposure to high-altitude (HA). Underlying mechanisms are not understood, but vascular shunting away from the gut could be responsible. Therefore, blood flow in the superior mesenteric artery (SMA) and hepatic portal vein (HPV) was examined at sea level (SL) and after ascent to 4392 m (HA).

MATERIALS AND METHODS

Twelve subjects [eight male, mean age 40 (22-72) years] were studied following an overnight fast and a standard meal. Cross-sectional vessel area and blood velocity were measured by ultrasound, systolic and diastolic flow calculated for the SMA (HR x vessel area x velocity, cm(3) min(-1)) and mean flow for the HPV.

RESULTS

All subjects experienced reduced appetite at HA. Blood flow in the SMA and HPV increased following food at SL (mean SMA systolic flow 1024 vs. 3316 cm(3) min(-1), P < 0.001; HPV 505 vs. 1789, P < 0.001) and at HA (2020 vs. 3767, P < 0.001; HPV 708 vs. 1727, P < 0.001). Pre-prandial flow in the SMA and HPV was significantly increased at HA compared with SL. The changes were due to increased vessel diameter and increased flow velocity. There was no difference in post-prandial flow between SL and HA in the HPV, although the increase in post-prandial flow was greater at SL than HA (254% increase vs. 144%).

CONCLUSIONS

These results show that resting blood flow in the gastrointestinal tract is increased during exposure to high-altitude hypoxia, and that the vascular response of increased blood flow following food ingestion is maintained. Therefore, reduced flow is unlikely to cause gastrointestinal symptoms and reduced appetite at HA.

Nutrição para os praticantes de exercício em grandes altitudes

Quando o atleta ascende a uma grande altitude, ele é exposto a uma pressão barométrica reduzida, e os efeitos fisiológicos que acompanham estas mudanças da pressão atmosférica podem ter grande influência sobre o seu organismo e seu desempenho físico. Acredita-se que a hipóxia seja responsável pelo início de uma cascata de eventos sinalizadores que, ao final, levam à adaptação à altitude. A exposição aguda à hipóxia provoca sonolência, fadiga mental e muscular e prostração. Cefaléia, náusea e anorexia são sintomas provocados pela Doença Aguda das Montanhas, que pode ocorrer nos primeiros dias de permanência na altitude. Uma estratégia nutricional adequada é fundamental para que o organismo não sofra nenhum estresse adicional. O objetivo deste trabalho foi apresentar os principais efeitos da altitude sobre o organismo e sobre o desempenho físico, discutir e/ou sugerir recomendações nutricionais para esta situação e, se possível, apresentar uma orientação nutricional prática para o atleta na altitude. Algumas das principais conclusões encontradas foram: o consumo energético deve ser aumentado; é fundamental monitorar a quantidade de líquidos ingeridos e escolher alimentos agradáveis ao paladar, ricos em energia e nutrientes. Recomenda-se trabalhar com um nutricionista do esporte com antecedência, para que um plano alimentar individual seja elaborado e colocado em prática antes mesmo da viagem à altitude.

Weight loss at high altitude: pathophysiology and practical implications

Climbers at high altitude (>5000 m) lose weight. This impairs performance and safety, but the mechanisms are not entirely due to an imbalance between energy intake and expenditure. There is some evidence of carbohydrate malabsorption, but there are also changes in fat metabolism and total body water. This paper considers the physiological control of weight and then discusses the changes in each parameter before addressing the practical implications.

Evidence against redox regulation of energy homoeostasis in humans at high altitude

The present study examined if free radicals and associated inflammatory sequelae influenced metabolic biomarkers involved in the neuro-endocrinological regulation of energy homoeostasis at high altitude. Sixteen mountaineers (11 males/five females) were matched for physical fitness and caloric intake and assigned in a double-blind manner to either antioxidant (n=8) or placebo (n=8) supplementation, which was enforced for 7 days at sea level and during an 11-day ascent to 4780 m. Enteral prophylaxis incorporated a daily bolus dose of 1 g of L-ascorbate, 400 international units of D,L-α-tocopherol acetate and 600 mg of α-lipoic acid. EPR (electron paramagnetic resonance) spectroscopic detection of PBN (α-phenyl-tert-butylnitrone) adducts confirmed an increase in the venous concentration of carbon-centred radicals at high altitude in the placebo group, whereas a decrease was observed in the antioxidant group (P<0.05 compared with that at sea level). EPR detection of DMSO/A˙− (DMSO-supplemented ascorbate free radical) demonstrated that the increase in carbon-centred radicals at high altitude was associated with a decrease in ascorbate (r2=0.63; P<0.05). Ascent to high altitude (pooled placebo+antioxidant groups) also increased the expression of pro-inflammatory cytokines (P<0.05 compared with that at sea level) and biomarkers of skeletal tissue damage (P<0.05). Despite a general decrease in leptin, insulin and glucose at high altitude (pooled placebo+antioxidant groups; P<0.05 compared with that at sea level), persistent anorexia resulted in a selective loss of body fat (P<0.05). In conclusion, antioxidant prophylaxis decreased the concentration of carbon-centred radicals at high altitude (P<0.05 compared with the placebo group), but did not influence markers of inflammation, appetite-related peptides, ad libitum nutrient intake or body composition. Thus free radicals do not appear to be involved in the inflammatory response and subsequent control of eating behaviour at high altitude.

Symptoms of infection and acute mountain sickness; associated metabolic sequelae and problems in differential diagnosis

Infections and acute mountain sickness (AMS) are common at high altitude, yet their precise etiologies remain elusive and the potential for differential diagnosis is considerable. The present study was therefore designed to compare clinical nonspecific symptoms associated with these pathologies and basic changes in free radical and amino-acid metabolism. Nineteen males were examined at rest and after maximal exercise at sea level before (SL(1)/SL(2)) and following a 20 +/- 5 day ascent to Kanchenjunga base camp located at 5100 m (HA). Four subjects with symptoms consistent with an ongoing respiratory and recent gastrointestinal infection were also diagnosed with clinical AMS on the evening of day 1 at HA. These and six other subjects recovering from symptoms consistent with a respiratory infection presented with a greater increase (HA minus SL(1)) in AMS scores and resting venous concentration of lipid hydroperoxides (LH) and in total creatine phosphokinase and ratio of free tryptophan/branched chain amino acids, and greater decrease in glutamine (Gln) compared to healthy controls (n = 9, p < 0.05). The decrease in Gln was consistently related to the altitude/exercise-induced increase in LH (r = -0.69/r = -0.45; p < 0.05) and altitude-induced increase in myoglobin (r = -0.73, p < 0.05). These findings highlight the potential for the misdiagnosis of altitude illness due to the similarity of nonspecific constitutional symptoms associated with infection and AMS. Both conditions were characterized by parallel changes in peripheral biomarkers related to free-radical, skeletal muscle damage and amino acid metabolism. While clearly not establishing cause and effect, free radical-mediated changes in peripheral amino acid metabolism known to influence immune and cerebral serotoninergic function may enhance susceptibility to and/or delay recovery from altitude illness.

Work at high altitude and oxidative stress: antioxidant nutrients

A significant portion of the world's geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS) and less frequently, high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The symptoms of AMS (headache, nausea, anorexia, fatigue, lassitude) occur in those who travel too high, too fast. Some investigators have linked the development of these symptoms with the condition of altered blood-brain barrier permeability, possibly related to hypoxia induced free radical formation. The burden of oxidative stress increases during the time spent at altitude and may even persist for some time upon return to sea level. The physiological and medical consequences of increased oxidative stress engendered by altitude is unclear; indeed, hypoxia is believed to be the trigger for the cascade of signaling events that ultimately leads to adaptation to altitude. These signaling events include the generation of reactive oxygen species (ROS) that may elicit important adaptive responses. If produced in excess, however, these ROS may contribute to impaired muscle function and reduced capillary perfusion at altitude or may even play a role in precipitating more serious neurological and pulmonary crisis. Oxidative stress can be observed at altitude without strenuous physical exertion; however, environmental factors other than hypoxia, such as exercise, UV light exposure and cold exposure, can also contribute to the burden. Providing antioxidant nutrients via the diet or supplements to the diet can reduce oxidative stress secondary to altitude exposure. In summary, the significant unanswered question concerning altitude exposure and antioxidant supplementation is when does oxidative stress become potentially damaging enough to merit antioxidant therapy and conversely, what degree of oxidative stress is necessary to foster the adaptive response of altitude exposure?

Failure of polycythemia-induced increase in arterial oxygen content to suppress the anorexic effect of simulated high altitude in the adult rat

The anorexic effect of exposure to high altitude may be related to the reduction in the arterial oxygen content (Ca(O2)) induced by hypoxemia and possibly the associated decreased convective oxygen transport (COT). This study was then performed to evaluate the effects of either transfusion-induced polycythemia or previous acclimation to hypobaria with endogenously induced polycythemia on the anorexic effect of simulated high altitude (SHA) in adult female rats. Food consumption, expressed in g/d/100 g body weight, was reduced by 40% in rats exposed to 506 mbar for 4 d, as compared to control rats maintained in room air. Transfusion polycythemia, which significantly increased hematocrit, hemoglobin concentration, Ca(O2), and COT, did not change the anorexic response to the exposure to hypobaric air. Depression of food intake during exposure to SHA also occurred in rats fasted during 31 h before exposure and allowed to eat ad libitum for 2 h during exposure. Body mass loss was similar in 48-h fasted rats that were either hypoxic or normoxic. Body mass loss was similar in normoxic and hypoxic rats, the former eating the amount of food freely eaten by the latter. Hypoxia-acclimated rats with endogenously induced polycythemia taken to SHA again had diminished food intake and lost body mass at rates that were very close to those found in nonacclimated ones. Exposure to SHA also led to a decrease in food consumption, body weight, and plasma leptin in adult female mice. Analysis of data suggest that body mass loss that accompanies SHA-induced hypoxia is due to hypophagia and that experimental manipulation of the blood oxygen transport capacity cannot ameliorate it. Leptin does not appear to be an inducer of the anorexic response to hypoxia, at least in mice and rats.

Weight loss at high altitude

Loss of appetite and weight are frequently observed at altitudes above 5000 m. However, the pathophysiology behind changes in body composition at extreme altitude is still not fully understood. Proper acclimatization to altitude and high caloric intake minimizes, but can not completely prevent significant weight loss under the influence of hypobaric hypoxia. The discovery of leptin in 1994 has initiated a new research area investigating molecular networks that connect peripheral organs with the central nervous system to sense and regulate energy intake as well as energy expenditure. Since then, a whole microcosm of new hormones, neurotransmitters and receptors has been discovered and studied with respect to body weight control. Those agents include neuropeptide Y (NPY), agouti-related protein (AGRP), melanocortin receptors (MC-R), cocaine-amphetamine regulated transcript (CART), pro-opiomelanocortin (POMC), orexin A and B (hypocretins), melanin-concentrating hormone (MCH) and ghrelin (endogenous ligand of the growth hormone secretagogue receptor). This overview will introduce the current concepts of the molecular control of energy homeostasis and attempt to reexamine the effects of altitude on appetite and body composition in light of these concepts. An overview of studies on changes of appetite and body composition at high altitude will be followed by the presentation of recent data on changes of endocrine parameters at hypobaric hypoxia that could be involved in the pathophysiology of weight loss.

Acute mountain sickness; prophylactic benefits of antioxidant vitamin supplementation at high altitude

Acute mountain sickness; prophylactic benefits of Free-radical-mediated damage to the blood-brain barrier may be implicated in the pathophysiology of acute mountain sickness (AMS). To indirectly examine this, we conducted a randomized double-blind placebo-controlled trial to assess the potentially prophylactic benefits of enteral antioxidant vitamin supplementation during ascent to high altitude. Eighteen subjects aged 35 +/- 10 years old were randomly assigned double-blind to either an antioxidant (n = 9) or placebo group (n = 9). The antioxidant group ingested 4 capsules/day(-1) (2 after breakfast/2 after evening meal) that each contained 250 mg of L-ascorbic acid, 100 IU of dl-a-tocopherol acetate and 150 mg of alpha-lipoic acid. The placebo group ingested 4 capsules of identical external appearance, taste, and smell. Supplementation was enforced for 3 weeks at sea level and during a 10-day ascent to Mt. Everest base camp (approximately 5,180 m). Antioxidant supplementation resulted in a comparatively lower Lake Louise AMS score at high altitude relative to the placebo group (2.8 +/- 0.8 points versus 4.0 +/- 0.4 points, P = 0.036), higher resting arterial oxygen saturation (89 +/- 5% versus 85 +/- 5%, P = 0.042), and total caloric intake (13.2 +/- 0.6 MJ/day(-1) versus 10.1 +/- 0.7 MJ/day(-1), P = 0.001); the latter is attributable to a lower satiety rating following a standardized meal. These findings indicate that the exogenous provision of water and lipid-soluble antioxidant vitamins at the prescribed doses is an apparently safe and potentially effective intervention that can attenuate AMS and improve the physiological profile of mountaineers at high altitude.