
==== Front
Int J Appl Basic Med Res
Int J Appl Basic Med Res
IJABMR
Int J App Basic Med Res
International Journal of Applied and Basic Medical Research
2229-516X
2248-9606
Wolters Kluwer - Medknow India

IJABMR-14-151
10.4103/ijabmr.ijabmr_55_24
Original Article
Exposure to Various Degrees and Durations of Hypobaric Hypoxia Causes a Reduction in Body Weight of Female Adult Rats
Yadav Anil Kumar 1
Yadav Bhupendra Singh 1
Yadav Pramod Kumar 2
Pandey Sada Nand 2
Sarvottam Kumar 13
1 Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India
2 Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India
3 Department of Physiology, All India Institute of Medical Sciences, Gorakhpur, Uttar Pradesh, India
Address for correspondence: Dr. Kumar Sarvottam, Department of Physiology, All India Institute of Medical Sciences, Gorakhpur, Uttar Pradesh, India. E-mail: kumarsarvo@gmail.com
Jul-Sep 2024
24 8 2024
14 3 151155
07 2 2024
10 5 2024
01 7 2024
Copyright: © 2024 International Journal of Applied and Basic Medical Research
2024
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.
Background:

Hypobaric hypoxia refers to a condition where there is a decreased oxygen partial pressure in the air due to low atmospheric pressure. It is known to affect the metabolism, leading to increased basal metabolic rate, alterations in appetite, and changes in cellular metabolism and energy homeostasis. The effects of hypoxia on metabolism and weight loss are influenced by genetic factors, gender, and the duration and severity of exposure to hypoxia. Currently, there are no reports which elucidate the impact of hypobaric hypoxia on female laboratory rats.

Objective:

The aim of this study was to observe the effect of varying degrees and durations of hypobaric hypoxia on the body weight of female rats.

Materials and Methods:

In this study, the body weight of 36 laboratory rats divided into six groups was taken at day 0, and then, the rats were exposed to hypobaric hypoxia in a specially designed hypoxia chamber and their body weights were recorded after 5 days and 10 days of hypoxia exposure. The change in body weight at 5 days and 10 days was compared to that of their body weight before the exposure to hypoxia. Data analysis was performed using IBM SPSS version 20.

Results:

Body weight was reduced in all rats subjected to varying degrees and duration of hypoxia. The percentage change in body weight was higher in moderate and severe hypoxia than in the mild hypoxia group. No significant difference was observed in rats exposed to varying degrees of hypoxia for 5 days as compared to those exposed for 10 days.

Conclusion:

Hypoxia may cause a reduction in body weight of female rats proportionate to the increasing severity of hypoxia and this reduction remains independent of the duration of exposure to hypoxia.

Body weight
female rats
hypobaric hypoxia
hypoxia
==== Body
pmcIntroduction

At higher altitudes, the air is less dense, resulting in a lower oxygen concentration per unit volume. This decreased oxygen availability can result in hypoxia, a condition in which organs and tissues in the body receive insufficient oxygen to meet their physiological requirements.[1] Hypobaric hypoxia refers to a condition characterized by reduced oxygen availability at lower atmospheric pressures. It influences several aspects of cell function, including growth, metabolism, and cell cycle.[2]

The effect of hypoxia extends across neurological, respiratory, and reproductive systems driven by cellular and subcellular alterations.[23] Hypobaric hypoxia can have significant physiological effects on living organisms, including humans, as the body must adapt to reduced oxygen availability to maintain normal function. These adaptations can include an increase in red blood cell production, changes in breathing patterns, and alterations in metabolic processes.[4]

Studies have shown that in response to hypoxia, there is a significant reduction in body weight.[5] This weight loss can be attributed to several factors, including dehydration in the hypobaric chamber, reduced appetite, dysfunctional digestive system, and malabsorption of nutrients.[3] A previously published study reported that hypobaric hypoxia can lead to increased glycolysis and reduced oxidative phosphorylation in skeletal muscle.[67] In addition, hypoxic training has been shown to regulate hepatic fatty acid metabolism in obese mice.[89] These findings suggest that hypobaric hypoxia may affect metabolic pathways such as oxidative phosphorylation and glycolysis, which could contribute to the observed changes in metabolic parameters.[6789]

The effects of hypoxia on weight loss are also influenced by genetic factors and the duration and severity of exposure to hypoxia.[3] In addition, there are gender differences in the way hypoxia-mediated weight loss occurs. Studies have shown that women tend to have fewer body weight variations brought on by altitude than males.[10] Bai et al. have shown that exposure to hypobaric hypoxia produces a significant effect on the body weight of rats, resulting in negative body weight gain.[11] The underlying mechanisms are not fully understood, but changes in metabolic processes and hypoxia-induced stress may play a role. In the currently available studies, the exposure to hypoxia is often combined with an increase in physical activity like continuous hiking and trekking sessions to difficult terrains and exercise[1213141516171819] or dietary modifications[15181920212223] often combined with decrease in ambient temperature at high altitude. Moreover, studies on hypoxia-mediated weight loss have focused on male rats, and there is a relative paucity of research specifically examining the effect of hypoxia on female rats. Understanding potential sex-specific differences in the response to hypoxia and the underlying mechanisms is an important area for future investigation. However, no such data are present that can correlate the effect of various degrees and durations of hypobaric hypoxia on the body weight of female rats. To date, the relationship between the duration and severity of hypoxia exposure and the extent of weight loss in female rats is also not well-defined. Determining the critical thresholds and understanding the dose-response relationship will provide valuable insights into the factors influencing weight loss under hypoxic conditions. Hence, through this study, we aimed to observe the effect of varying degrees and durations of hypobaric hypoxia on the body weight of female rats.

Materials and Methods

All the experiments were carried out using young female rats and adult female rats of (The Charles-Foster strain) following the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA) guideline after approval from the Institutional Animal Ethical Committee (IAEC), Banaras Hindu University (No. Dean/2021/IAEC/3028).

A total of 36 female rats (Rattus norvegicus) of Charles foster strain aged approximately 6 months old were used in this study. These rats were further divided into six groups, each corresponding to a different combination of degree (mild [670 mmHg], moderate [560 mmHg] and severe [450 mmHg]), and duration [5 days and 10 days] of hypoxia.

For exposure to different grades of hypobaric hypoxia, the rats were kept in a specially designed chamber for simulation of different environmental conditions (Patent application number 202311027550) for different time durations. The rats were maintained under a controlled temperature of 24°C ± 2°C and a light-dark cycle of 12 h with access to food and water ad libitum.

Their body weight was recorded at Day 0 and Day 5/Day 10 at all three degrees of hypoxia. The change in body weight at 5 days and 10 days was compared to that of their body weight before the exposure to hypoxia using the Wilcoxon Signed-rank test. Comparison between mild, moderate, and severe hypoxia groups was performed using Kruskal–Wallis one-way analysis of variance. The body weight of rats exposed to respective degrees of hypoxia was compared among 5-day and 10-day exposure groups using the Mann–Whitney U-test. Data analysis was performed using the statistical software IBM SPSS Statistics Version 20 (International Business Machine corporation , Armonk, New York, USA). “P < 0.05” was deemed statistically significant.

Results

The findings, as mentioned in Figures 1 and 2, indicate that exposure to hypoxia leads to a significant reduction in the body weight of female rats. The rats were exposed to either mild hypoxia (670 mmHg), moderate hypoxia (560 mmHg), or severe hypoxia (450 mmHg) for the duration of either 5 days or 10 days. The body weight of female rats declined after both 5 days and 10 days of exposure to hypoxia in a dose-dependent manner. When the percentage change in body weight was calculated, no significant percentage change in body weight was observed between 5 days of exposure to hypoxia and 10 days of exposure to hypoxia. When compared among the groups, the percentage change in body weight in response to hypoxia was higher in the moderate group and severe group than in the mild group; however, no significant change was observed between the moderate and severe groups. When all the groups were compared to each other, it was observed that the percentage change in body weight in the 10-day moderate hypoxia-treated group was significantly higher than the percentage change in body weight of the 5-day and 10-day mild hypoxia-treated groups. In addition, the percentage change in body weight in the 10-day severe hypoxia-treated group was significantly higher than in the 10-day mild hypoxia-treated group. The percentage change in body weight in the 5-day moderate and severe hypoxia-treated groups was significantly higher than the 10-day mild hypoxia-treated group. The maximum percent change in body weight was seen in the 10-day moderate hypoxia-treated group. These findings suggest that exposure to hypoxia negatively impacts weight gain in female rats.

Figure 1 Graphical representation of change in body weight (in gm.) of female rats subjected to mild, moderate, and severe hypoxia after 5 days and 10 days compared to initial body weight

Figure 2 Graphical representations of percentage change in body weight of adult female rats subjected to mild, moderate, and severe hypoxia for 5 days compared to those subjected to mild, moderate, and severe hypoxia for 10 days

Discussion

Hypobaric hypoxia is commonly experienced by individuals who live at high altitudes or engage in activities such as mountaineering, aviation, or space travel. It is well-documented that hypoxia impacts body weight at high altitudes through complex mechanisms involving changes in metabolism, energy expenditure, and appetite.[24] The effects of hypoxia on body weight may depend on factors of hypoxia exposure duration and severity, gender as well as individual physiological responses. In this study, we report the negative weight gain in female rats exposed to hypoxia. The percent change in body weight is greater among the moderate and severe hypoxia-treated groups in both 5 days and 10 days of exposure to hypoxia. However, not much change was observed between moderate-treated and severe hypoxia-treated groups. Maximum change in body weight was seen in moderate hypoxia-treated groups exposed to 10 days of hypoxia. These changes in body weight depend on hypoxia exposure duration and severity of hypoxia exposure, gender as well as individual physiological responses of rats.

One key factor involved in these metabolic changes is the activation of hypoxia-inducible factor (HIF). Hypoxia-induced HIF activation can be crucial for weight loss due to its involvement in the regulation of metabolism and energy homeostasis.[252627] HIF-α and HIF-β subunits are degraded by prolyl hydroxylases (PHDs) under conditions of normoxia, but under hypoxia, PHD activity is inhibited, promoting stabilization and accumulation of HIF-α.[26272829] Altitude-induced HIF-1α activation may upregulate leptin mRNA levels, improve leptin sensitivity, suppress appetite, and increase glucose metabolism and angiogenic genes, leading to increased energy expenditure and weight loss.[293031] Hypobaric hypoxia significantly impacts cellular respiration, causing a shift from oxidative phosphorylation to glycolysis.[32] This adaptation enables cells to maintain ATP production even during conditions of low oxygen availability.[33] HIF activation leads to increased transcription of glycolysis-related genes and downregulation of oxidative phosphorylation genes. However, this shift may be less efficient and contribute to increased basal metabolic rate at high altitudes.[3334] Moreover, the exposure to hypoxia also upregulates the expression of glucose transporter 1, facilitating glucose uptake, and supporting energy production through glycolysis.[3536] This adaptation helps to maintain cellular energy balance and may contribute to the metabolic changes associated with weight loss in hypoxic conditions. Hypoxia has been found to have a suppressive effect on appetite. Previously published reports have indicated that hypoxia exposure can lead to a decrease in appetite and energy intake by regulating the production and release of appetite-regulating hormones, such as leptin and ghrelin.[37383940]

In addition, there is evidence of sexual dimorphism in the metabolic responses to altitude exposure, suggesting hormonal influences on HIF activity.[35] Males and females exhibit different metabolic adaptations to hypoxia, with males showing increased glucose utilization and potential weight loss. The specific hormonal factors underlying these sex-specific responses require further investigation. According to a study conducted by Bai et al., rats exposed to hypoxia for 3 weeks had a mean body weight that was 20.3% lower than rats exposed to normal oxygen levels.[11] We also observed similar results in female rats.

Rats have metabolic pathways and physiological responses that are similar to humans, making them a relevant model for studying the effects of hypoxia on body weight. Multiple studies have correlated hypoxia-mediated negative weight gain in male rats to the hormonal and physiological homeostasis of rats and humans. However, no such studies had been conducted on female rats. In this study, we have shown the effect of hypoxia on the body weight of female rats. This will pave the way for the investigation of the metabolic adaptations that occur in response to hypoxia, such as changes in energy expenditure, nutrient utilization, and hormonal regulation of appetite in females. We have compared the percent change in body weight at different doses and durations of hypobaric hypoxia, findings of which can be useful in studying hypoxia-related changes in females at high altitudes. In this study, we have not investigated the molecular mechanisms behind the weight loss in female rats. While reduced food intake and metabolic adaptations are commonly cited mechanisms for weight loss in hypoxia, other factors such as changes in water balance, muscle wasting, or alterations in gut microbiota may also contribute to the observed effects. It is important to consider and investigate these alternative mechanisms to gain a comprehensive understanding of the weight reduction observed in hypobaric hypoxia studies.

Conclusion

The study concludes that there is a significant decrease in the body weight of female rats exposed to hypobaric hypoxia. The findings of this study are significant to high-altitude acclimatization research because they provide a model to study the physiological and molecular mechanisms underlying weight loss in response to hypoxia, which is a common feature of high-altitude exposure. In addition, the findings can contribute to the development of targeted interventions and potential therapeutic strategies for managing weight loss or metabolic disorders associated with hypoxia in both animal models and human populations.

Ethical statement

The study was approved by the Institutional Animal Ethical Committee (IAEC), of Banaras Hindu University, Varanasi, U.P. India (No. Dean/2021/IAEC/3028).

Financial support and sponsorship

The study was financially supported by the Indian Council of Medical Research through Ad-hoc project grant: File No. 5/10/FR/05/2021-RBMCH (PI-KS). AKY received his doctoral fellowship from the University Grant Commission, Ministry of Education Government of India: F. No. 16-9 (June 2017)/2018(NET/CSIR).

Conflicts of interest

There are no conflicts of interest.
==== Refs
1 Luo Z Tian M Yang G Tan Q Chen Y Li G Hypoxia signaling in human health and diseases: Implications and prospects for therapeutics Signal Transduct Target Ther 2022 7 218 35798726
2 Yadav AK Yadav PK Chaudhary GR Tiwari M Gupta A Sharma A Autophagy in hypoxic ovary Cell Mol Life Sci 2019 76 3311 22 31062072
3 Michiels C Physiological and pathological responses to hypoxia Am J Pathol 2004 164 1875 82 15161623
4 West JB Respiratory system under stress Respiratory Physiology, the Essentials Philadelphia Lippincott Williams and Wilkins 2012
5 Dünnwald T Gatterer H Faulhaber M Arvandi M Schobersberger W Body composition and body weight changes at different altitude levels: A systematic review and meta-analysis Front Physiol 2019 10 430 31057421
6 Murray AJ Metabolic adaptation of skeletal muscle to high altitude hypoxia: How new technologies could resolve the controversies Genome Med 2009 1 117 20090895
7 Horscroft JA Murray AJ Skeletal muscle energy metabolism in environmental hypoxia: Climbing towards consensus Extrem Physiol Med 2014 3 19 25473486
8 Wang R Guo S Tian H Huang Y Yang Q Zhao K Hypoxic training in obese mice improves metabolic disorder Front Endocrinol (Lausanne) 2019 10 527 31440207
9 Yang Q Sun S Liu W Liu Q Wang J Hypoxia training improves hepatic steatosis partly by downregulation of CB1 receptor in obese mice Biochem Biophys Res Commun 2020 525 639 45 32122652
10 Braun B Mawson JT Muza SR Dominick SB Brooks GA Horning MA Women at altitude: Carbohydrate utilization during exercise at 4,300 m J Appl Physiol (1985) 2000 88 246 56 10642387
11 Bai G Yang B Tong W Li H Hypobaric hypoxia causes impairment of spermatogenesis in developing rats at pre-puberty Andrologia 2018 50 e13000
12 Chen MT Lee WC Chen SC Chen CC Chen CY Lee SD Effect of a prolonged altitude expedition on glucose tolerance and abdominal fatness Res Q Exerc Sport 2010 81 472 7 21268471
13 Greie S Humpeler E Gunga HC Koralewski E Klingler A Mittermayr M Improvement of metabolic syndrome markers through altitude specific hiking vacations J Endocrinol Invest 2006 29 497 504 16840826
14 Gunga HC Fries D Humpeler E Kirsch K Boldt LE Koralewski E Austrian Moderate Altitude Study (AMAS 2000) –Fluid shifts, erythropoiesis, and angiogenesis in patients with metabolic syndrome at moderate altitude (congruent with 1700 m) Eur J Appl Physiol 2003 88 497 505 12560947
15 Hoyt RW Jones TE Baker-Fulco CJ Schoeller DA Schoene RB Schwartz RS Doubly labeled water measurement of human energy expenditure during exercise at high altitude Am J Physiol 1994 266 R966 71 8160893
16 Beidleman BA Fulco CS Cadarette BS Cymerman A Buller MJ Salgado RM Is normobaric hypoxia an effective treatment for sustaining previously acquired altitude acclimatization? J Appl Physiol (1985) 2017 123 1214 27 28705998
17 Subudhi AW Bourdillon N Bucher J Davis C Elliott JE Eutermoster M AltitudeOmics: The integrative physiology of human acclimatization to hypobaric hypoxia and its retention upon reascent PLoS One 2014 9 e92191 24658407
18 Fulco CS Friedlander AL Muza SR Rock PB Robinson S Lammi E Energy intake deficit and physical performance at altitude Aviat Space Environ Med 2002 73 758 65 12182215
19 Fulco CS Kambis KW Friedlander AL Rock PB Muza SR Cymerman A Carbohydrate supplementation improves time-trial cycle performance during energy deficit at 4,300-m altitude J Appl Physiol (1985) 2005 99 867 76 15879171
20 Schena F Guerrini F Tregnaghi P Kayser B Branched-chain amino acid supplementation during trekking at high altitude. The effects on loss of body mass, body composition, and muscle power Eur J Appl Physiol Occup Physiol 1992 65 394 8 1425642
21 Berryman CE Young AJ Karl JP Kenefick RW Margolis LM Cole RE Severe negative energy balance during 21 d at high altitude decreases fat-free mass regardless of dietary protein intake: A randomized controlled trial FASEB J 2018 32 894 905 29066613
22 Debevec T Bali TC Simpson EJ Macdonald IA Eiken O Mekjavic IB Separate and combined effects of 21-day bed rest and hypoxic confinement on body composition Eur J Appl Physiol 2014 114 2411 25 25091855
23 Holm L Haslund ML Robach P van Hall G Calbet JA Saltin B Skeletal muscle myofibrillar and sarcoplasmic protein synthesis rates are affected differently by altitude-induced hypoxia in native lowlanders PLoS One 2010 5 e15606 21187972
24 Palmer BF Clegg DJ Ascent to altitude as a weight loss method: The good and bad of hypoxia inducible factor activation Obesity (Silver Spring) 2014 22 311 7 23625659
25 Gonzalez FJ Xie C Jiang C The role of hypoxia-inducible factors in metabolic diseases Nat Rev Endocrinol 2018 15 21 32 30275460
26 Zhang F Wu W Deng Z Zheng X Zhang J Deng S High altitude increases the expression of hypoxia-inducible factor 1? and inducible nitric oxide synthase with intest-inal mucosal barrier failure in rats Int J Clin Exp Pathol 2015 8 5189 95 26191216
27 Ziello JE Jovin IS Huang Y Hypoxia-Inducible Factor (HIF)-1 regulatory pathway and its potential for therapeutic intervention in malignancy and ischemia Yale J Biol Med 2007 80 51 60 18160990
28 Gaspar JM Velloso LA Hypoxia inducible factor as a central regulator of metabolism –Implications for the development of obesity Front Neurosci 2018 12 813 30443205
29 Strowitzki MJ Cummins EP Taylor CT Protein hydroxylation by Hypoxia-Inducible Factor (HIF) hydroxylases: Unique or ubiquitous? Cells 2019 8 384 31035491
30 Dewi S Yulhasri Y Mulyawan W The impact of intermittent hypobaric hypoxia exposures on triacylglycerol synthesis in rat liver Rep Biochem Mol Biol 2021 10 437 44 34981021
31 Matsuura H Ichiki T Inoue E Nomura M Miyazaki R Hashimoto T Prolyl hydroxylase domain protein 2 plays a critical role in diet-induced obesity and glucose intolerance Circulation 2013 127 2078 87 23630130
32 Wheaton WW Chandel NS Hypoxia. 2. Hypoxia regulates cellular metabolism Am J Physiol Cell Physiol 2011 300 C385 93 21123733
33 Semenza GL HIF-1 mediates metabolic responses to intratumoral hypoxia and oncogenic mutations J Clin Invest 2013 123 3664 71 23999440
34 Mallet RT Burtscher J Pialoux V Pasha Q Ahmad Y Millet GP Molecular mechanisms of high-altitude acclimatization Int J Mol Sci 2023 24 1698 36675214
35 Mamun AA Hayashi H Yamamura A Nayeem MJ Sato M Hypoxia induces the translocation of glucose transporter 1 to the plasma membrane in vascular endothelial cells J Physiol Sci 2020 70 44 32962633
36 Sadlecki P Bodnar M Grabiec M Marszalek A Walentowicz P Sokup A The role of Hypoxia-inducible factor-1 ?, glucose transporter-1, (GLUT-1) and carbon anhydrase IX in endometrial cancer patients Biomed Res Int 2014 2014 616850 24745019
37 Debevec T Hypoxia-related hormonal appetite modulation in humans during rest and exercise: Mini review Front Physiol 2017 8 366 28611686
38 Gatterer H Roche J Turner R Vinetti G Roveri G Schlittler M Changes in body mass, appetite-related hormones, and appetite sensation in women during 4 days of hypobaric hypoxic exposure equivalent to 3,500-m altitude J Appl Physiol (1985) 2023 134 133 41 36476162
39 Rausch LK Hofer M Pramsohler S Kaser S Ebenbichler C Haacke S Adiponectin, leptin and visfatin in hypoxia and its effect for weight loss in obesity Front Endocrinol (Lausanne) 2018 9 615 30405530
40 Mirzaei Bavil F Alipour MR Keyhanmanesh R Alihemmati A Ghiyasi R Mohaddes G Ghrelin decreases angiogenesis, HIF-1? and VEGF protein levels in chronic hypoxia in lung tissue of male rats Adv Pharm Bull 2015 5 315 20 26504752
