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Neuroendocrine response to acute and...

Wright, Heather Elizabeth.

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Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males./
Author:	Wright, Heather Elizabeth.
Description:	331 p.
Notes:	Source: Dissertation Abstracts International, Volume: 71-09, Section: B, page: 5306.
Contained By:	Dissertation Abstracts International71-09B.
Subject:	Biology, Endocrinology. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=NR64969
ISBN:	9780494649695

Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males.
Wright, Heather Elizabeth.

Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males. - 331 p.

Source: Dissertation Abstracts International, Volume: 71-09, Section: B, page: 5306.

Thesis (Ph.D.)--York University (Canada), 2010.

Increases in rectal temperature (Tre) augment stress hormones, however the effect of different Tre tolerated with varying fitness levels during exertional heat stress (EHS) is unclear. Heat acclimation is known to increase tolerance time and Tre tolerated, and reduce physiological strain, yet it is unknown if repeated EHS reduces the hypothalamic-pituitary- adrenal (HPA) axis, sympathetic-adrenomedullary system (SAS) response, and indicators of central fatigue (CF) at any given level of thermal strain. PURPOSE: To examine the HPA axis, SAS, and indicators of CF during acute EHS in trained (TR) versus untrained (UT) (study 1) and during repeated EHS in UT males (study 2). METHODS: Subjects walked to exhaustion (EXH) on a treadmill (4.5 km·h-1, 2% incline) in 40°C (dry), wearing combat clothing and a protective hooded overgarment, for acute and repeated (9 days over 11 days) sessions. Study 1 included 12 TR and 11 UT (V&dot;O2peak = 70+/-2 and 50+/-1 mLkgLBM1&dot;min -1) and study 2 included 9 UT (V&dot;O2peak = 51.7+/-1.9 mLkgLBM-1&dot;min-1) males. Venous blood samples were obtained at rest (PRE; prior to heat) and at a Tre of38, 38.5, 39, 39.5, 40.0°C and/or EXH. Hormone analyses were completed by chemiluminescence, gas chromatography/mass spectrometry, and enzyme immunoassay. RESULTS: Study 1: Cortisol (COR) responded to absolute thermal strain, increasing throughout EHS and independent of fitness. Adrenocorticotropic hormone (ACTH), norepinephrine (NE), and dehydroepiandrosterone-sulphate (DHEA-S) responded to relative thermal strain. Epinephrine (E), growth hormone (GH), and aldosterone (ALDO) increased initially, with a plateau above 38.5°C Tre (Manuscript I). Free tryptophan (f-TRP) exhibited a significant fall at 39.5°C for TR (II). Study 2: NE, ACTH, DHEA-S, and ALDO responded to relative thermal strain, COR and E to absolute thermal strain, and GH exhibited a plateau effect beyond 38.0°C on Day 9 (III). f-TRP was attenuated and branch chain amino acids (BCAA) elevated on Day 9 (IV). Prolactin (PRL) increased linearly with Tre. CONCLUSION: The stress pathways responded largely to relative thermal strain, although some hormones exhibited a clamping response likely as a protective mechanism. For the TR, evidence existed for a reduced pituitary sensitivity to glucocorticoids and the amplified GH may have contributed to their greater Tre tolerated. The significant fall in f-TRP at 39.5°C for acute TR and attenuated f-TRP and elevated BCAAs on Day 9 is consistent with loss of blood-brain barrier integrity and reduced CF, respectively. PRL is a critically important marker of fatigue given its strong relationship with Tre.

ISBN: 9780494649695Subjects--Topical Terms:

1682242
Biology, Endocrinology.

Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males.
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100 1 $a Wright, Heather Elizabeth. $3 1684053
245 1 0 $a Neuroendocrine response to acute and repeated exertional heat stress in endurance trained and untrained males.
300 $a 331 p.
500 $a Source: Dissertation Abstracts International, Volume: 71-09, Section: B, page: 5306.
502 $a Thesis (Ph.D.)--York University (Canada), 2010.
520 $a Increases in rectal temperature (Tre) augment stress hormones, however the effect of different Tre tolerated with varying fitness levels during exertional heat stress (EHS) is unclear. Heat acclimation is known to increase tolerance time and Tre tolerated, and reduce physiological strain, yet it is unknown if repeated EHS reduces the hypothalamic-pituitary- adrenal (HPA) axis, sympathetic-adrenomedullary system (SAS) response, and indicators of central fatigue (CF) at any given level of thermal strain. PURPOSE: To examine the HPA axis, SAS, and indicators of CF during acute EHS in trained (TR) versus untrained (UT) (study 1) and during repeated EHS in UT males (study 2). METHODS: Subjects walked to exhaustion (EXH) on a treadmill (4.5 km·h-1, 2% incline) in 40°C (dry), wearing combat clothing and a protective hooded overgarment, for acute and repeated (9 days over 11 days) sessions. Study 1 included 12 TR and 11 UT (V&dot;O2peak = 70+/-2 and 50+/-1 mLkgLBM1&dot;min -1) and study 2 included 9 UT (V&dot;O2peak = 51.7+/-1.9 mLkgLBM-1&dot;min-1) males. Venous blood samples were obtained at rest (PRE; prior to heat) and at a Tre of38, 38.5, 39, 39.5, 40.0°C and/or EXH. Hormone analyses were completed by chemiluminescence, gas chromatography/mass spectrometry, and enzyme immunoassay. RESULTS: Study 1: Cortisol (COR) responded to absolute thermal strain, increasing throughout EHS and independent of fitness. Adrenocorticotropic hormone (ACTH), norepinephrine (NE), and dehydroepiandrosterone-sulphate (DHEA-S) responded to relative thermal strain. Epinephrine (E), growth hormone (GH), and aldosterone (ALDO) increased initially, with a plateau above 38.5°C Tre (Manuscript I). Free tryptophan (f-TRP) exhibited a significant fall at 39.5°C for TR (II). Study 2: NE, ACTH, DHEA-S, and ALDO responded to relative thermal strain, COR and E to absolute thermal strain, and GH exhibited a plateau effect beyond 38.0°C on Day 9 (III). f-TRP was attenuated and branch chain amino acids (BCAA) elevated on Day 9 (IV). Prolactin (PRL) increased linearly with Tre. CONCLUSION: The stress pathways responded largely to relative thermal strain, although some hormones exhibited a clamping response likely as a protective mechanism. For the TR, evidence existed for a reduced pituitary sensitivity to glucocorticoids and the amplified GH may have contributed to their greater Tre tolerated. The significant fall in f-TRP at 39.5°C for acute TR and attenuated f-TRP and elevated BCAAs on Day 9 is consistent with loss of blood-brain barrier integrity and reduced CF, respectively. PRL is a critically important marker of fatigue given its strong relationship with Tre.
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