Ingestion of cold (<10°C) compared to warm (>37°C) fluid has been suggested to attenuate heat storage levels during exercise. However, modulations in sweat output may yield differences in evaporative heat loss that are greater than differences in heat transfer with the ingested fluid. The purpose of the thesis was to evaluate thermoregulatory control and human heat balance, and compare thermometrically derived values of heat storage with those derived from partitional calorimetry following water ingestion of varying temperature during exercise. We found that water ingestion of 50°C compared to 1.5°C decreases heat storage in thermoneutral environments, and further exacerbates the error of thermometric heat storage estimations. Differences in heat storage were attributed exclusively to disproportionate reductions in whole-body and local sweat output and thus evaporative heat loss potential. Ingested fluid temperature only minimally altered skin blood flow and did not influence dry heat exchange with the ambient environment.

This study sought to determine the independent influence of hypoxia on thermoregulatory responses to exercise in compensable and uncompensable hot conditions. Eight participants completed three experimental trials of cycling in either normoxia (21% O2) or hypoxia (13% O2) in order to manipulate relative exercise intensity (%VO2peak), since VO2peak was reduced by ~30% in hypoxia. When trials were matched for %VO2peak, changes in core temperature and local sweat rates (LSR) were significantly lower in the hypoxic trial as a result of a lower rate of metabolic heat production (Hprod) in order to maintain a similar %VO2peak compared to normoxia. However, when Hprod was fixed between normoxic and hypoxic trials the systematic differences in core temperature and LSR were eliminated. Conversely, at a fixed Hprod skin blood flow (SkBF) was greater in hypoxia compared to normoxia by ~40%. Despite improvements in SkBF, the potential for maximum heat loss was unaffected during an incremental humidity ramp protocol, resulting in no difference between normoxia and hypoxia in the critical ambient vapour pressures at which core temperature inflected upwards. These data further demonstrate, using a within-subjects design, that metabolic heat production, irrespective of large differences in %VO2peak, determines thermoregulatory responses during exercise. Furthermore, this study suggests that the influence of large differences in skin blood flow on heat dissipation may be lesser than previously thought.

Females exhibit lower sudomotor response than males, which has been attributed to physiological differences between sexes. It is well accepted that non-thermal factors (i.e. baroreceptors and osmoreceptors) can influence thermoeffector responses. Even though there are sex-related differences in baroreceptor modulation of thermoeffector responses, it remains unknown if differences in osmoreceptor modulation could explain the lower sudomotor response in females. Therefore, we examined if there are sex-related differences in osmoreceptor modulation of sweating and cutaneous vascular conductance (CVC). A group of nine males and nine females were passively heated while in an isosmotic and hyperosmotic state. The onset and thermosensitivity of sweating and CVC were calculated and compared between groups and conditions. We show that the delay in onset of sweating and CVC is similar between sexes. However, thermosensitivity of sweating was lower in females than males. We conclude that hyperosmolality does not modulate the decreased sudomotor activity in females.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.

Crianças frequentemente realizam atividades físicas em ambientes quentes. O calor pode afetar o desempenho, conforto subjetivo, tolerância ao exercício e ser preocupante para a saúde. Além disso, parece que crianças obesas, comparadas com as magras, apresentam desvantagens ao se exercitarem no calor. Devido à importância do exercício aeróbio para o manejo da obesidade e promoção da saúde, essas diferenças merecem ser elucidadas, principalmente em meninas, devido à escassez de informações. Objetivo: Comparar as respostas termorregulatórias e perceptivas de meninas pré-púberes magras e obesas durante e após uma sessão de exercício, de similar intensidade relativa, em condição ambiental termoneutra e de calor. Métodos: Para a revisão da literatura, foram selecionados artigos com as palavras chaves: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration e acclimatization. No estudo experimental, vinte e sete meninas ativas e aclimatizadas, alocadas nos grupos magras e obesas conforme a adiposidade (≤ 25% para as magras e  30% para as obesas) medida pelo DXA, participaram do estudo. Elas pedalaram (carga de 55% do VO2pico) e recuperaram (sentadas) por 30 minutos numa condição termoneutra e outra de calor, com água disponível para ser ingerida à vontade. A temperatura retal (Tre), frequência cardíaca (FC), taxa de percepção de esforço (TPE), sensação térmica, conforto térmico e irritabilidade foram avaliados periodicamente. A sudorese foi avaliada, e durante o exercício no calor foi coletada uma amostra de suor para análise da concentração de eletrólitos (Na+, Cl- e K+). Resultados: Revisão — estudos com meninos indicam que os obesos parecem ser prejudicados nas respostas termorregulatórias durante exercício no calor relacionado: prejuízos na dissipação por convecção devido à menor área de superfície corporal (ASC) pela massa corporal; a menor taxa de sudorese, condicionamento físico, tolerância ao exercício e capacidade de aclimatação ao calor; ao maior custo metabólico para locomoção; e prejuízo na dissipação de calor pela maior gordura subcutânea. Não foram encontrados estudos comparando as respostas termorregulatórias de meninas magras e obesas no calor; e os estudos com o sexo feminino apresentam resultados parcialmente contraditórios ao masculino. Experimento — a Tre inicial foi maior nas obesas nas duas sessões (no calor 37,5 ± 0,3 vs. 37,3 ± 0,3 ºC, e na termoneutra 37,6 ± 0,3 vs. 37,3 ± 0,2 ºC; p = 0,03) e se manteve durante o exercício; e a magnitude do aumento foi maior nas magras, sendo que no calor a Tre final ultrapassou a das obesas (37,8 ± 0,2 vs. 38,0 ± 0,2 ºC; p = 0,04). As magras relataram diminuição do conforto térmico (p = 0,009) e aumento da irritação (p = 0,02) no decorrer do exercício. A FC, respostas perceptivas de TPE e sensação térmica foram semelhantes entre os grupos, assim como as respostas de sudorese. Observou-se maior concentração de Na+ no suor nas obesas (78,7 ± 47,5 vs. 50,5 ± 12,1 mEql-1; p = 0,04). Conclusão: Meninas obesas apresentaram maior Tre inicial, e as magras apresentaram uma maior magnitude de aumento na Tre, principalmente no calor, acompanhada de maior desconforto térmico e irritabilidade. / Children often perform physical activities in hot environments. The heat can affect performance, subjective comfort, exercise tolerance and cause concern for health. Moreover, it seems that obese children, compared with the lean, have disadvantages while exercising in the heat. Given the importance of aerobic exercise for obesity management and health promotion, these differences should be elucidated, especially in girls due to the information lack. Aim: To compare the thermoregulatory responses and perceptual between lean and obese pre-pubertal girls during and after an exercise session, at similar relative effort intensity in the thermoneutral environmental and heat. Methods: For the literature review, articles were selected using the keywords: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration and acclimatization. In the experimental trial, twenty-seven active and acclimatized girls, placed in groups lean and obese according to fat percentage (≤ 25% for lean and  30% for the obese) measured by DXA, participated in this study. They cycled (charge 55% of VO2peak) and recovered (seated) for 30 minutes in a thermoneutral condition and in the heat, with hydration ad libitum. Rectal temperature (Tre), heart rate (HR), rate of perceived exertion (RPE), thermal sensation, thermal comfort and irritability were assessed periodically. Sweating was evaluated, and during exercise in the heat a sample sweat was collected to electrolytes concentration (Na+, Cl- and K+) analysis. Results: Review — obese children appear to be impaired in thermoregulatory responses during exercise in the heat related to: the convection damage dissipation due to less body surface area (BSA) by body mass, the lower sweating rate, fitness, exercise tolerance and to heat acclimation ability, the higher locomotion metabolic cost, and heat dissipation loss for greater subcutaneous fat. Any study had compared the thermoregulatory responses between lean and obese girls in heat. Trial — the initial Tre was higher in obese in both sessions (in the heat 37.5 ± 0.3 vs 37.3 ± 0.3 ºC and in thermoneutral 37.6 ± 0.3 vs. 37.3 ± 0 2 º C, p = 0.03) and was maintained during exercise, and magnitude of the increase was greater in lean, mainly in the heat when the final Tre surpassed the obese (37.8 ± 0.2 vs. 38.0 ±0.2 ºC, p = 0.04). The thermal comfort has decreased (p = 0.009) and irritation has increased (p = 0.02) in the lean during the exercise. HR, sweating responses and perceptual responses of TPE and thermal sensation were similar between groups. A higher concentration of Na+ in sweat was observed in obese (78.7 ± 47.5 vs 50.5 ± 12.1 mEql-1, p = 0.04). Conclusion: Initial Tre were higher in obese group, and lean had a greater magnitude of increase in Tre, especially during exercise in the heat, accompanied by thermal discomfort and irritability increased.

Crianças frequentemente realizam atividades físicas em ambientes quentes. O calor pode afetar o desempenho, conforto subjetivo, tolerância ao exercício e ser preocupante para a saúde. Além disso, parece que crianças obesas, comparadas com as magras, apresentam desvantagens ao se exercitarem no calor. Devido à importância do exercício aeróbio para o manejo da obesidade e promoção da saúde, essas diferenças merecem ser elucidadas, principalmente em meninas, devido à escassez de informações. Objetivo: Comparar as respostas termorregulatórias e perceptivas de meninas pré-púberes magras e obesas durante e após uma sessão de exercício, de similar intensidade relativa, em condição ambiental termoneutra e de calor. Métodos: Para a revisão da literatura, foram selecionados artigos com as palavras chaves: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration e acclimatization. No estudo experimental, vinte e sete meninas ativas e aclimatizadas, alocadas nos grupos magras e obesas conforme a adiposidade (≤ 25% para as magras e  30% para as obesas) medida pelo DXA, participaram do estudo. Elas pedalaram (carga de 55% do VO2pico) e recuperaram (sentadas) por 30 minutos numa condição termoneutra e outra de calor, com água disponível para ser ingerida à vontade. A temperatura retal (Tre), frequência cardíaca (FC), taxa de percepção de esforço (TPE), sensação térmica, conforto térmico e irritabilidade foram avaliados periodicamente. A sudorese foi avaliada, e durante o exercício no calor foi coletada uma amostra de suor para análise da concentração de eletrólitos (Na+, Cl- e K+). Resultados: Revisão — estudos com meninos indicam que os obesos parecem ser prejudicados nas respostas termorregulatórias durante exercício no calor relacionado: prejuízos na dissipação por convecção devido à menor área de superfície corporal (ASC) pela massa corporal; a menor taxa de sudorese, condicionamento físico, tolerância ao exercício e capacidade de aclimatação ao calor; ao maior custo metabólico para locomoção; e prejuízo na dissipação de calor pela maior gordura subcutânea. Não foram encontrados estudos comparando as respostas termorregulatórias de meninas magras e obesas no calor; e os estudos com o sexo feminino apresentam resultados parcialmente contraditórios ao masculino. Experimento — a Tre inicial foi maior nas obesas nas duas sessões (no calor 37,5 ± 0,3 vs. 37,3 ± 0,3 ºC, e na termoneutra 37,6 ± 0,3 vs. 37,3 ± 0,2 ºC; p = 0,03) e se manteve durante o exercício; e a magnitude do aumento foi maior nas magras, sendo que no calor a Tre final ultrapassou a das obesas (37,8 ± 0,2 vs. 38,0 ± 0,2 ºC; p = 0,04). As magras relataram diminuição do conforto térmico (p = 0,009) e aumento da irritação (p = 0,02) no decorrer do exercício. A FC, respostas perceptivas de TPE e sensação térmica foram semelhantes entre os grupos, assim como as respostas de sudorese. Observou-se maior concentração de Na+ no suor nas obesas (78,7 ± 47,5 vs. 50,5 ± 12,1 mEql-1; p = 0,04). Conclusão: Meninas obesas apresentaram maior Tre inicial, e as magras apresentaram uma maior magnitude de aumento na Tre, principalmente no calor, acompanhada de maior desconforto térmico e irritabilidade. / Children often perform physical activities in hot environments. The heat can affect performance, subjective comfort, exercise tolerance and cause concern for health. Moreover, it seems that obese children, compared with the lean, have disadvantages while exercising in the heat. Given the importance of aerobic exercise for obesity management and health promotion, these differences should be elucidated, especially in girls due to the information lack. Aim: To compare the thermoregulatory responses and perceptual between lean and obese pre-pubertal girls during and after an exercise session, at similar relative effort intensity in the thermoneutral environmental and heat. Methods: For the literature review, articles were selected using the keywords: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration and acclimatization. In the experimental trial, twenty-seven active and acclimatized girls, placed in groups lean and obese according to fat percentage (≤ 25% for lean and  30% for the obese) measured by DXA, participated in this study. They cycled (charge 55% of VO2peak) and recovered (seated) for 30 minutes in a thermoneutral condition and in the heat, with hydration ad libitum. Rectal temperature (Tre), heart rate (HR), rate of perceived exertion (RPE), thermal sensation, thermal comfort and irritability were assessed periodically. Sweating was evaluated, and during exercise in the heat a sample sweat was collected to electrolytes concentration (Na+, Cl- and K+) analysis. Results: Review — obese children appear to be impaired in thermoregulatory responses during exercise in the heat related to: the convection damage dissipation due to less body surface area (BSA) by body mass, the lower sweating rate, fitness, exercise tolerance and to heat acclimation ability, the higher locomotion metabolic cost, and heat dissipation loss for greater subcutaneous fat. Any study had compared the thermoregulatory responses between lean and obese girls in heat. Trial — the initial Tre was higher in obese in both sessions (in the heat 37.5 ± 0.3 vs 37.3 ± 0.3 ºC and in thermoneutral 37.6 ± 0.3 vs. 37.3 ± 0 2 º C, p = 0.03) and was maintained during exercise, and magnitude of the increase was greater in lean, mainly in the heat when the final Tre surpassed the obese (37.8 ± 0.2 vs. 38.0 ±0.2 ºC, p = 0.04). The thermal comfort has decreased (p = 0.009) and irritation has increased (p = 0.02) in the lean during the exercise. HR, sweating responses and perceptual responses of TPE and thermal sensation were similar between groups. A higher concentration of Na+ in sweat was observed in obese (78.7 ± 47.5 vs 50.5 ± 12.1 mEql-1, p = 0.04). Conclusion: Initial Tre were higher in obese group, and lean had a greater magnitude of increase in Tre, especially during exercise in the heat, accompanied by thermal discomfort and irritability increased.

Crianças frequentemente realizam atividades físicas em ambientes quentes. O calor pode afetar o desempenho, conforto subjetivo, tolerância ao exercício e ser preocupante para a saúde. Além disso, parece que crianças obesas, comparadas com as magras, apresentam desvantagens ao se exercitarem no calor. Devido à importância do exercício aeróbio para o manejo da obesidade e promoção da saúde, essas diferenças merecem ser elucidadas, principalmente em meninas, devido à escassez de informações. Objetivo: Comparar as respostas termorregulatórias e perceptivas de meninas pré-púberes magras e obesas durante e após uma sessão de exercício, de similar intensidade relativa, em condição ambiental termoneutra e de calor. Métodos: Para a revisão da literatura, foram selecionados artigos com as palavras chaves: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration e acclimatization. No estudo experimental, vinte e sete meninas ativas e aclimatizadas, alocadas nos grupos magras e obesas conforme a adiposidade (≤ 25% para as magras e  30% para as obesas) medida pelo DXA, participaram do estudo. Elas pedalaram (carga de 55% do VO2pico) e recuperaram (sentadas) por 30 minutos numa condição termoneutra e outra de calor, com água disponível para ser ingerida à vontade. A temperatura retal (Tre), frequência cardíaca (FC), taxa de percepção de esforço (TPE), sensação térmica, conforto térmico e irritabilidade foram avaliados periodicamente. A sudorese foi avaliada, e durante o exercício no calor foi coletada uma amostra de suor para análise da concentração de eletrólitos (Na+, Cl- e K+). Resultados: Revisão — estudos com meninos indicam que os obesos parecem ser prejudicados nas respostas termorregulatórias durante exercício no calor relacionado: prejuízos na dissipação por convecção devido à menor área de superfície corporal (ASC) pela massa corporal; a menor taxa de sudorese, condicionamento físico, tolerância ao exercício e capacidade de aclimatação ao calor; ao maior custo metabólico para locomoção; e prejuízo na dissipação de calor pela maior gordura subcutânea. Não foram encontrados estudos comparando as respostas termorregulatórias de meninas magras e obesas no calor; e os estudos com o sexo feminino apresentam resultados parcialmente contraditórios ao masculino. Experimento — a Tre inicial foi maior nas obesas nas duas sessões (no calor 37,5 ± 0,3 vs. 37,3 ± 0,3 ºC, e na termoneutra 37,6 ± 0,3 vs. 37,3 ± 0,2 ºC; p = 0,03) e se manteve durante o exercício; e a magnitude do aumento foi maior nas magras, sendo que no calor a Tre final ultrapassou a das obesas (37,8 ± 0,2 vs. 38,0 ± 0,2 ºC; p = 0,04). As magras relataram diminuição do conforto térmico (p = 0,009) e aumento da irritação (p = 0,02) no decorrer do exercício. A FC, respostas perceptivas de TPE e sensação térmica foram semelhantes entre os grupos, assim como as respostas de sudorese. Observou-se maior concentração de Na+ no suor nas obesas (78,7 ± 47,5 vs. 50,5 ± 12,1 mEql-1; p = 0,04). Conclusão: Meninas obesas apresentaram maior Tre inicial, e as magras apresentaram uma maior magnitude de aumento na Tre, principalmente no calor, acompanhada de maior desconforto térmico e irritabilidade. / Children often perform physical activities in hot environments. The heat can affect performance, subjective comfort, exercise tolerance and cause concern for health. Moreover, it seems that obese children, compared with the lean, have disadvantages while exercising in the heat. Given the importance of aerobic exercise for obesity management and health promotion, these differences should be elucidated, especially in girls due to the information lack. Aim: To compare the thermoregulatory responses and perceptual between lean and obese pre-pubertal girls during and after an exercise session, at similar relative effort intensity in the thermoneutral environmental and heat. Methods: For the literature review, articles were selected using the keywords: thermoregulation, obesity, children, girls, sweating, exercise, heat, hydration and acclimatization. In the experimental trial, twenty-seven active and acclimatized girls, placed in groups lean and obese according to fat percentage (≤ 25% for lean and  30% for the obese) measured by DXA, participated in this study. They cycled (charge 55% of VO2peak) and recovered (seated) for 30 minutes in a thermoneutral condition and in the heat, with hydration ad libitum. Rectal temperature (Tre), heart rate (HR), rate of perceived exertion (RPE), thermal sensation, thermal comfort and irritability were assessed periodically. Sweating was evaluated, and during exercise in the heat a sample sweat was collected to electrolytes concentration (Na+, Cl- and K+) analysis. Results: Review — obese children appear to be impaired in thermoregulatory responses during exercise in the heat related to: the convection damage dissipation due to less body surface area (BSA) by body mass, the lower sweating rate, fitness, exercise tolerance and to heat acclimation ability, the higher locomotion metabolic cost, and heat dissipation loss for greater subcutaneous fat. Any study had compared the thermoregulatory responses between lean and obese girls in heat. Trial — the initial Tre was higher in obese in both sessions (in the heat 37.5 ± 0.3 vs 37.3 ± 0.3 ºC and in thermoneutral 37.6 ± 0.3 vs. 37.3 ± 0 2 º C, p = 0.03) and was maintained during exercise, and magnitude of the increase was greater in lean, mainly in the heat when the final Tre surpassed the obese (37.8 ± 0.2 vs. 38.0 ±0.2 ºC, p = 0.04). The thermal comfort has decreased (p = 0.009) and irritation has increased (p = 0.02) in the lean during the exercise. HR, sweating responses and perceptual responses of TPE and thermal sensation were similar between groups. A higher concentration of Na+ in sweat was observed in obese (78.7 ± 47.5 vs 50.5 ± 12.1 mEql-1, p = 0.04). Conclusion: Initial Tre were higher in obese group, and lean had a greater magnitude of increase in Tre, especially during exercise in the heat, accompanied by thermal discomfort and irritability increased.

The objective of this study was to evaluate the effect of pregnancy, breed, and hair coat on body temperature and sweating rate (SR) of hair sheep. St. Croix White (STX; = 9) and Dorper × STX (DRPX; = 9) ewes (3.6 yr of age) were evaluated over 4 d at 126 d of gestation (PREG) and over 4 d at 46 d postpartum (OPEN) in the shade and sun and in the morning (AM; 0900 to 1200 h) and afternoon (PM; 1300 to 1600 h) after a 20 min acclimation to each condition on each day. Data loggers recorded vaginal temperature (VT) at 10-min intervals for 96 h. Rectal temperature (RT) was measured using a digital veterinary thermometer, and respiration rate (RR) was measured as breaths per minute (bpm). Sweating rate was calculated from measured air properties passing over a shaved (300 cm) and unshaved area of the ewes' body using a portable calorimeter. Data were analyzed using GLM procedures of SAS (SAS Inst. Inc., Cary, NC) with breed, pregnancy status, sun exposure, and time of day as main effects. Mean temperature, relative humidity, temperature-humidity index, wind speed, and solar radiation on the days of data collection were 28.2°C, 82.8%, 80.3, 4.2 km/h, and 237.5 W/m, respectively. There was no difference ( > 0.10) in RT, RR, and SR between DRPX and STX ewes. The PREG ewes had lower RT ( < 0.007) and SR ( < 0.0001) and higher RR ( < 0.007) than OPEN ewes (38.5 ± 0.2 vs. 39.1 ± 0.2°C, 70.2 ± 3.1 vs. 88.3 ± 3.1 g⋅m⋅h, and 79.5 ± 2.2 vs. 72.1 ± 2.2 bpm, respectively). During the PM, RR, RT ( < 0.05), and SR ( < 0.006) were higher than in the AM. In the sun, RR ( < 0.001) and SR ( < 0.0001) were higher than in the shade, but there was no difference ( > 0.10) in RT. There was no difference in SR ( > 0.10) between the shaved and unshaved area of the ewe. The DRPX ewes had higher ( < 0.0001) VT than STX ewes. The PREG ewes had higher ( < 0.001) VT than OPEN ewes during the night time and lower VT than the OPEN ewes during the day time ( < 0.0001). The OPEN ewes had a greater ( < 0.009) daily range of VT than PREG ewes did (2.5 ± 0.4 vs. 1.1 ± 0.4°C, respectively), but there was no breed difference ( > 0.10). Hair coat did not have an influence on the SR of the ewes, and PREG ewes appeared to use increased respiration as opposed to sweating to help control RT. The narrower range of body temperature, measured as VT, of PREG compared to OPEN ewes may be a protective mechanism for the developing fetus.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.