Open AccessAcute Neuroendocrine Response to Uncompensable Heat Stress in Endurance TVained Versus Untrained Males
Author(s) -
Heather E. Wright,
Glen A. Selkirk,
Tom M. McLellan
Publication year - 2007
Publication title -
medicine and science in sports and exercise
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.703
H-Index - 224
eISSN - 1530-0315
pISSN - 0195-9131
DOI - 10.1249/01.mss.0000274203.21713.6e
Subject(s) - epinephrine , endocrinology , serotonin , norepinephrine , medicine , hormone , treadmill , rectal temperature , hyperthermia , dopamine , thermoregulation , heat stress , catecholamine , zoology , biology , receptor
Understanding the neuroendocrine stress response to heat stress in trained (TR) versus untrained (UT) individuals may assist in identifying the mechanisms behind improved thermotolerance in TR individuals. Present knowledge suggests that an increase in rectal temperature (Tre) augments the stress response and corresponding hormone and neurotransmitter changes. However, the impact of Tre on the stress hormones in TR and UT individuals is unclear.PURPOSE: The purpose of this study was to examine the neuroendocrine response to acute uncompensable heat stress in TR compared to UT individuals at the same rectal temperatures.METHODS: Eleven TR (Mean \ub1 SE: VO2peak= 68 \ub1 1 mL-kgLBM-l-mm-1, 11 \ub1 1 % fat, 24.0 \ub1 1.2y) and nine UT (VO2peak= 50 \ub1 1 mL-kgLBM-l-min-1, 15 \ub1 1% fat, 23.6 \ub1 1.6y) males walked to exhaustion on a treadmill (4.5 km-h-1, 2% grade) in 40\ub0C and 30% R.H. while wearing combat clothing and a protective overgarment with hood. Venous blood samples were obtained at baseline (prior to heat stress), and at a Tre of 38.0, 38.5, 39.0\ub0C, and exhaustion. Blood was centrifuged, separated, and serum/plasma stored frozen until analyzed for dopamine (DA), norepinephrine (NE), epinephrine (E), and serotonin (5-HT) using gas chromatography/mass spectrometry.RESULTS: Peak Tre reached was 39.7 \ub1 0.1\ub0C for TR and 39.1 \ub1 0.1\ub0C for UT, with exercise times of 165 \ub1 12 min for TR and 106 \ub1 11 min for UT. At the same absolute intensity of exercise, there were no differences in DA from baseline to a Tre 39\ub0C between TR and UT, however, DA was significantly elevated at exhaustion compared to baseline. In contrast, E and NE increased similarly for both groups with increasing Tre from baseline (Mean \ub1 SE: E=94 \ub1 17 and 80 \ub1 21 pg\ub7mL-1, NE=362 \ub1 33 and 346 \ub1 31 pg\ub7mL-1) to exhaustion (E=143 \ub1 28 and 153 \ub1 11 pg\ub7mL-1, NE=1133 \ub1 67 and 1204 \ub1 98 pg\ub7mL-1). Serotonin was significantly greater in TR (57 \ub1 12 ng\ub7mL-1) versus UT (19 \ub1 5 ng\ub7mL-1) throughout exercise to 39\ub0C and at exhaustion (TR=51 \ub1 16 ng\ub7mL-1 and UT=19 \ub1 4 ng\ub7mL-1).CONCLUSION: In summary, E and NE increased during acute uncompensable heat stress in proportion to the increases in Tre but changes were independent of fitness level, whereas 5-HT was increased with higher fitness levels. Elevations in DA were only detected at exhaustion in both groups.Peer reviewed: YesNRC publication: N