Copeptin reflects physiological strain during thermal stress

Abstract

PurposeTo prevent heat-related illnesses, guidelines recommend limiting core body temperature (T c) ≤ 38 °C during thermal stress. Copeptin, a surrogate for arginine vasopressin secretion, could provide useful information about fluid balance, thermal strain and health risks. It was hypothesised that plasma copeptin would rise with dehydration from occupational heat stress, concurrent with sympathoadrenal activation and reduced glomerular filtration, and that these changes would reflect T c responses.MethodsVolunteers (n = 15) were recruited from a British Army unit deployed to East Africa. During a simulated combat assault (3.5 h, final ambient temperature 27 °C), T c was recorded by radiotelemetry to differentiate volunteers with maximum T c > 38 °C versus ≤ 38 °C. Blood was sampled beforehand and afterwards, for measurement of copeptin, cortisol, free normetanephrine, osmolality and creatinine.ResultsThere was a significant (P < 0.05) rise in copeptin from pre- to post-assault (10.0 ± 6.3 vs. 16.7 ± 9.6 pmol L−1, P < 0.001). Although osmolality did not increase, copeptin correlated strongly with osmolality after the exposure (r = 0.70, P = 0.004). In volunteers with maximum T c > 38 °C (n = 8) vs ≤ 38 °C (n = 7) there were significantly greater elevations in copeptin (10.4 vs. 2.4 pmol L−1) and creatinine (10 vs. 2 μmol L−1), but no differences in cortisol, free normetanephrine or osmolality.ConclusionsChanges in copeptin reflected T c response more closely than sympathoadrenal markers or osmolality. Dynamic relationships with tonicity and kidney function may help to explain this finding. As a surrogate for integrated physiological strain during work in a field environment, copeptin assay could inform future measures to prevent heat-related illnesses.

Heat acclimatization blunts copeptin responses to hypertonicity from dehydrating exercise in humans

“…We have also reported a threshold effect of exercising Tc on copeptin response, independent of serum osmolality (Stacey et al. 2018a). The addition of a resting osmotic load test to our protocol may have helped to more definitively locate a change in osmotic sensitivity with acclimatization, independent of body temperature, but was not achievable within the constraints of the deployed study.…”

“…For example, the decline in end-exercise Tc with acclimatization may have reduced osmotic stimulus, as the osmoreceptor is known to show greater sensitivity at higher tissue temperatures (Takamata et al 1995;Sladek and Johnson 2013). We have also reported a threshold effect of exercising Tc on copeptin response, independent of serum osmolality (Stacey et al 2018a). The addition of a resting osmotic load test to our protocol may have helped to more definitively locate a change in osmotic sensitivity with acclimatization, independent of body temperature, but was not achievable within the constraints of the deployed study.…”

“…Sample size was calculated using G Power 3.1 (http:// www.psycho.uni-duesseldorf.de/abteilungen/aap/gpower3/). Based on the range and distribution of copeptin values reported in a similar population (Stacey et al 2018a), a sample of 22 volunteers was required to detect a 50% rise in copeptin at end exercise between Day 2 and Day 23 in Cyprus (power 0.85, alpha 0.05, effect size 0.22). Reductions in plasma volume from PRE to POST were estimated from the increase in total protein concentration (PRE minus POST) expressed as a percentage of PRE values.…”

Heat Adaptation in Military Personnel: Mitigating Risk, Maximizing Performance

“…Other studies have attempted to find surrogate markers including early reductions in heart rate and cortisol in the short term followed by diminished excitability by heart rate variability and nephrine measures with respect to LTHA (Stacey et al, 2018b). Elevated copeptin, a surrogate for arginine vasopressin secretion, measured before and after heat stress exposure in military subjects correlated with a core temperature rise greater than 38 • C in comparison with subjects where the core temperature rise was less than 38 • C (Stacey et al, 2018a). Whilst copeptin may be a surrogate for integrated physiological strain during work in a field environment it is unknown how this is influenced by heat adaptation.…”

The Female Heart: Sex Differences in the Dynamics of ECG in Response to Stress

“…Similarly, HF has also been suggested to be influenced by typical respiratory frequenc ies (Kenwright et al, 2009). In conclusion, the physiological interpretation of LF and HF cannot be verified without conducting an extensive endocrinological study into the relations hip between mental stress, LF, and HF, in which respiration is controlled (Stacey et al, 2018). Also, the spectral results reported here support the LF and HF normalisation method employed in this study.…”