Heat acclimation enhances the cold-induced vasodilation response

Cold exposure accelerates lysine catabolism to promote cold acclimation via remodeling hepatic histone crotonylation

BACKGROUND

Cold environments pose serious threats on human health, with increased risk for myocardial infarction, stroke, frostbite, and hypothermia. Acquired cold acclimation is required to minimize cold-induced injures and to improve metabolic health. However, the underlying mechanisms remain to be fully elucidated.

OBJECTIVE

We aimed to identify critical amino acids involved in cold acclimation and unmask the regulatory mechanisms.

METHODS

A total of twenty male participants were recruited and followed up after 3 months' natural cold exposure. Cold-induced vasodilation (CIVD) tests and clinical biochemical analysis were performed at baseline and after 3-months cold exposure, whilst blood samples were collected, and plasma amino acids were analyzed by targeted metabolomics. To further confirm the effect of lysine on cold tolerance and explain the latent mechanism, mice were challenged with chronic cold exposure for 7 days with lysine supplement, then core and local surface temperature as well as thermogenesis activity were detected.

RESULTS

Continuous cold exposure shortened the CIVD onset time and increased the average finger temperature. Levels of the plasma lysine and glycine were decreased in both humans and mice. Venn analysis from three datasets revealed that lysine was the only significantly changed plasma amino acid, which strongly correlated with the altered CIVD. Moreover, mice sustained a relatively higher core temperature and surface temperature in the back, tail and paws upon lysine supplementation. Furthermore, lysine supplementation increased the level of histone H3K18cr and promoted the gene and protein expression of Cpt1a, Cpt2 and Cyp27a1 in liver.

CONCLUSION

Our work identified lysine as a critical amino acid for the remodeling of hepatic histone crotonylation that facilitates cold acclimation.

Cross-adaptation from heat stress to hypoxia: A systematic review and exploratory meta-analysis

Cross-adaptation (CA) refers to the successful induction of physiological adaptation under one environmental stressor (e.g., heat), to enable subsequent benefit in another (e.g., hypoxia). This systematic review and exploratory meta-analysis investigated the effect of heat acclimation (HA) on physiological, perceptual and physical performance outcome measures during rest, and submaximal and maximal intensity exercise in hypoxia. Database searches in Scopus and MEDLINE were performed. Studies were included when they met the Population, Intervention, Comparison, and Outcome criteria, were of English-language, peer-reviewed, full-text original articles, using human participants. Risk of bias and study quality were assessed using the COnsensus based Standards for the selection of health status Measurement INstruments checklist. Nine studies were included, totalling 79 participants (100 % recreationally trained males). The most common method of HA included fixed-intensity exercise comprising 9 ± 3 sessions, 89 ± 24-min in duration and occurred within 39 ± 2 °C and 32 ± 13 % relative humidity. CA induced a moderate, beneficial effect on physiological measures at rest (oxygen saturation: g = 0.60) and during submaximal exercise (heart rate: g = -0.65, core temperature: g = -0.68 and skin temperature: g = -0.72). A small effect was found for ventilation (g = 0.24) and performance measures (peak power: g = 0.32 and time trial time: g = -0.43) during maximal intensity exercise. No effect was observed for perceptual outcome measures. CA may be appropriate for individuals, such as occupational or military workers, whose access to altitude exposure prior to undertaking submaximal activity in hypoxic conditions is restricted. Methodological variances exist within the current literature, and females and well-trained individuals have yet to be investigated. Future research should focus on these cohorts and explore the mechanistic underpinnings of CA.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 4: evolution, thermal adaptation and unsupported theories of thermoregulation

This review is the final contribution to a four-part, historical series on human exercise physiology in thermally stressful conditions. The series opened with reminders of the principles governing heat exchange and an overview of our contemporary understanding of thermoregulation (Part 1). We then reviewed the development of physiological measurements (Part 2) used to reveal the autonomic processes at work during heat and cold stresses. Next, we re-examined thermal-stress tolerance and intolerance, and critiqued the indices of thermal stress and strain (Part 3). Herein, we describe the evolutionary steps that endowed humans with a unique potential to tolerate endurance activity in the heat, and we examine how those attributes can be enhanced during thermal adaptation. The first of our ancestors to qualify as an athlete was Homo erectus, who were hairless, sweating specialists with eccrine sweat glands covering almost their entire body surface. Homo sapiens were skilful behavioural thermoregulators, which preserved their resource-wasteful, autonomic thermoeffectors (shivering and sweating) for more stressful encounters. Following emigration, they regularly experienced heat and cold stress, to which they acclimatised and developed less powerful (habituated) effector responses when those stresses were re-encountered. We critique hypotheses that linked thermoregulatory differences to ancestry. By exploring short-term heat and cold acclimation, we reveal sweat hypersecretion and powerful shivering to be protective, transitional stages en route to more complete thermal adaptation (habituation). To conclude this historical series, we examine some of the concepts and hypotheses of thermoregulation during exercise that did not withstand the tests of time.

Central versus peripheral mechanisms of cold-induced vasodilation: a study in the fingers and toes of people with paraplegia

PURPOSE

This study examined physiological and perceptual parameters related to cold-induced vasodilation (CIVD) in the fingers and toes of people with paraplegia and compared them with responses observed in able-bodied individuals.

METHODS

Seven participants with paraplegia and seven able-bodied individuals participated in a randomized matched-controlled study involving left-hand and -foot immersion in cold water (8 ± 1 °C) for 40 min during exposure to cool (16 ± 1 °C), thermoneutral (23 ± 1 °C), and hot (34 ± 1 °C) ambient conditions.

RESULTS

Similar CIVD occurrence was observed in the fingers in the two groups. In toes, three of the seven participants with paraplegia revealed CIVDs: one in cool, two in thermoneutral, and three in hot conditions. No able-bodied participants revealed CIVDs in cool and thermoneutral conditions, while four revealed CIVDs in hot conditions. The toe CIVDs of paraplegic participants were counterintuitive in several respects: they were more frequent in cool and thermoneutral conditions (compared to the able-bodied participants), emerged in these conditions despite lower core and skin temperatures of these participants, and were evident only in cases of thoracic level lesions (instead of lesions at lower spinal levels).

CONCLUSION

Our findings demonstrated considerable inter-individual variability in CIVD responses in both the paraplegic and able-bodied groups. While we observed vasodilatory responses in the toes of participants with paraplegia that technically fulfilled the criteria for CIVD, it is unlikely that they reflect the CIVD phenomenon observed in able-bodied individuals. Taken together, our findings favor the contribution of central over peripheral factors in relation to the origin and/or control of CIVD.

Cardiovascular Stress and Characteristics of Cold-Induced Vasodilation in Women and Men during Cold-Water Immersion: A Randomized Control Study

BACKGROUND

Cold-induced vasodilation (CIVD) is a phenomenon that refers to a paradoxical increase in finger temperature that sometimes occurs during cold exposure. The aim of this study was to compare CIVD responses between women and men, during exposure to different environmental conditions.

METHODS

Seven men and seven women participated in a matched controlled study consisting of a familiarization protocol followed by three experimental sessions (cool (10.8 °C WBGT), thermoneutral (17.2 °C WBGT), and hot (27.2 °C WBGT)). In each session, participants were asked to immerse their left hand and foot in warm water (35 ± 1 °C) for five minutes. Thereafter, the left hand and foot were immersed in cold water (8 ± 1 °C) for 40 min. After that, the left hand and foot were removed from the water and participants remained seated for five minutes.

RESULTS

For a matched thermal stress, women experienced an elevated cardiovascular strain (heart rate and in some cases mean arterial pressure) and higher frequency of CIVD reactions (men: 31 vs. women: 60) in comparison to their male counterparts.

CONCLUSIONS

The present study demonstrated that women experienced elevated cardiovascular strain and higher frequency of CIVD reactions, particularly in the toes, compared to their male counterparts during cold-water immersion.