This study is the first to examine the effects of core temperature elevation on kynurenine pathway (KP) metabolites in healthy young males. It was hypothesized that rise in core temperature due to both pasive heating and exercise will initiate a stress response, affecting the concentration of KP metabolites. Additionally, it was expected that the exercise would produce more pronounced effects due to the increased cardiovascular, mechanical, and metabolic demands associated with it. Thus, the the main purpose of the present study was to investigate and to compare the effects of two distinct heat stress modalities on KP metabolites.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
SINGLE
Enrollment
11
Exercise was used as the endogenous heating modality, the participant cycled at 60% of his VO2max until rectal temperature reached 39°C
Hot-water immersion was used as the exogenous heating modality, where the participants sat immersed in a water bath at 43.5 ± 0.5°C and remained submerged until rectal temperature reached 39°C.
Lithuanian Sports University
Kaunas, Lithuania
Change in plasma metabolites of the kynurenine pathway (μm)
An ultra-performance liquid chromatography-tandem mass spectrometry system (UPLC-MS/MS) was used to measure venous plasma levels of tryptophan, kynurenine, kynurenic acid, 3-hydroxy-kynurenine, quinolinic acid, nicotinamide and picolinic acid (in μm). The UPLC-MS/MS system uses a Xevo TQ-XS triple quadrupole mass spectrometer (Waters) with a Z-spray electrospray interface, and the system operates in electrospray positive multiple reaction monitoring mode.
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Rectal temperature (°C)
Rectal temperature (in °C) was measured using a thermocouple (Rectal Probe, Ellab, Denmark) inserted to a depth of 12 cm past the anal sphincter.
Time frame: Day 1 (during both heating modalities until Tre reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Change in heart rate (bpm)
Heart rate (in bpm) was recorded using a heart rate sensor with a chest strap (Polar, Finland).
Time frame: Day 1 (during both heating modalities until Tre reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Change in physiological strain index
A physiological strain index (PSI) was used to indicate heat strain. PSI = 5 x (Tret - Tre0) x (39.5 - Tre0)\^-1+ 5 x (HRt - HR0) x (180 - HR0)\^-1, where rectal temperature (Tre) t and heart rate (HR) t are simultaneous measurements taken every 0.5°C of the heat exposure and Tre0 and HR0 are the initial measurements.
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Change in glucose (mmol/L)
The glucose concentration (in mmol/L) was measured using an automatic blood glucose meter Glucocard X-mini-Plus (Arkray Inc, Japan).
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
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Change in lactate (mmol/L)
The lactate concentration (in mmol/L) was measured using an Accutrend Plus System (Roche, Germany).
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Changes in prolactin concentration (ng/mL)
The venous prolactin (in ng/mL) was measured using enzyme-linked immunosorbent assay kit and a Spark multimode microplate reader (Tecan, Austria).
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Changes in catecholamines concentration (ng/mL)
The venous adrenaline and noradrenaline concentrations (in ng/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)
Changes in salivary cortisol concentration (µg/dL)
The saliva samples was collected to measure cortisol level (in µg/dL) using an ELISA kits and a Spark multimode microplate reader (Tecan, Austria).
Time frame: Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)