The Effect of Heat Exposure on Physiological Markers

NCT07064512 | Completed

• 1 other identifier: LithuananianSportsU-24
• Study Type: interventional
• Target: 11
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Healthy Adult Male

Outcome Measures

Primary Outcomes (9)

• 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.

  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.

  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).

  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.

  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).

  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 lactate (mmol/L)

  The lactate concentration (in mmol/L) was measured using an Accutrend Plus System (Roche, Germany).

  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).

  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).

  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).

  Day 1 (every 0.5 °C until rectal temperature (Trec) reached 39°C, followed by a recovery phase until Trec reached 37.5°C)

Study Arms (2)

Exogenous heating

EXPERIMENTAL

Healthy young subjects participated received 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.

Other: Exogenous heating

Endogenous heating

EXPERIMENTAL

Healthy young subjects participated received endogenous heating modality, the participant cycled at 60% of his VO2max until rectal temperature reached 39°C

Other: Endogenous heating

Interventions

Endogenous heating OTHER

Exercise was used as the endogenous heating modality, the participant cycled at 60% of his VO2max until rectal temperature reached 39°C

Endogenous heating

Exogenous heating OTHER

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.

Exogenous heating

Eligibility Criteria

• Age: 18 Years - 36 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• healthy adults;
• age between 18 - 36 years;
• physically active (exercising 2-3 times per week);
• non-smoking.

You may not qualify if:

• a body mass index (BMI) \> 30 kg/m2;
• neurological, cardiovascular, metabolic, and/or inflammatory diseases, or conditions that could be worsened by exposure to interventions and that could affect experimental variables;
• involvement in temperature manipulation program for ≥ 3 months.

Sponsors & Collaborators

• Lithuanian Sports University: lead

Study Sites (1)

Lithuanian Sports University

Kaunas, Lithuania

Location

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: July 11, 2025
• First Posted: July 14, 2025
• Study Start: January 11, 2021
• Primary Completion: March 12, 2021
• Study Completion: March 12, 2021
• Last Updated: July 17, 2025

Record last verified: 2025-07

Locations

LI (1)