Involvement of the hypothalamic-pituitary-thyroid axis and its interaction with the hypothalamic-pituitary-adrenal axis in the ontogeny of avian thermoregulation: a review

The emergence of thermoregulation in avian species is a complex matter in which neural as well as hormonal processes are involved. In a previous paper, the neural aspects of primary avian thermoregulation were discussed. In this paper the role of the hypothalamus-pituitary-thyroid axis (HPT-axis) and the hypothalamus-pituitary-adrenal axis (HPA-axis) in the ontogeny of avian thermoregulation is evaluated. The regulatory mechanisms and different important hormones of both axes, which have stimulatory or inhibitory effects, are discussed. Because the onset of functionality of the thermoregulatory system is of great interest, the ontogeny and functionality of the hormonal axes are clarified. There is a great difference between precocial and altricial birds in hormonal events as well as in neural processes which are involved in the emergence of thermoregulation. In precocial avian species the HPT-axis becomes functional during the mid- to late embryonic period while the same axis only becomes fully functional during the first week post-hatch in altricial avian species. As early as the sixties, the emergence of homeothermy in chickens was investigated. It was concluded that the thyroid gland plays an important role in the thermoregulatory mechanisms of newly hatched chicks. More recent studies however were not able to show any direct effect of the thyroid hormones on the thermoregulation of day-old chicks, although blocking the conversion of T4 to T3 caused a decrease in body temperature in young chicks. Thyrotropin releasing hormone (TRH) is known to act in thermoregulation in mammals and several authors have found an effect of TRH on the metabolism of young and older chicks. However, the exact mechanism still remains unclear. Because the HPT- and the HPA-axis show close relationships, the role of the HPA-axis in the ontogeny of thermoregulation is also taken into consideration in this review. In mammals as well as in birds, corticotropin releasing hormone (CRH) is involved in the primary thermoregulation. We conclude that the HPT-axis has an important role in the ontogeny of avian thermoregulation. The exact role of the HPA-axis remains largely unclear although at least CRH is definitely of some importance

Thermoregulation During Spaceflight

The purpose of this flight proposal is to investigate human thermoregulatory parameters during exercise in microgravity. The hypothesis to be tested is that microgravity-adopted astronauts will exhibit accentuated increases in their core temperature (excess hyperthermia) during exercise because of altered heat loss responses due to reduced sweating and/or accentuated vasodilation. The specific aims are (1) to compare core and skin temperature responses during moderate exercise before flight and inflight; (2) to determine whether the hypothesized inflight excessive hyperthermia is due to increased heat production, reduced, sweating, impaired peripheral vasodilation, or to some combination of these factors; and (3) to determine whether heat production at an exercise load of 60 percent of the maximal working capacity is similar preflight and inflight. It is expected that the astronauts will exhibit excessive hyperthermia during exposure to microgravity which will be caused by decreased sweating and decreased skin blood flow

Expansion of a mathematical model of thermoregulation to include high metabolic rates Final report, Jun. 19, 1967 - Jun. 18, 1968

Mathematical model of human thermoregulation with high metabolic rate

The Effects of Men\u27s Lacrosse Protective Equipment on Thermoregulation and Perceptions During Exercise Heat Stress

The effects of men\u27s lacrosse protective equipment on thermoregulation and perceptions during exercise heat stress Amanda P. Glasgow: Exercise Science Research Center, University of Arkansas, Fayetteville, AR. Background: Exertional heat stroke and other heat related illnesses are a common concern for athletic coaches and players. Looking to prevent further injuries, it is questioned whether players perceive if their bodies are heating to a dangerous level. Many factors play into the body’s response and the players perception including thirst, thermoregulation, and the kind of protective equipment the athletes are wearing. Purpose: Examine if perceptual responses are different when participants wear men’s lacrosse protective equipment compared to when they do not. Our hypothesis was that reported perceptual responses would be different between equipment and non-equipment trials. Methodology: We recruited 12 healthy males ages 21.8 ± 3.35 with heights 181.29 cm ± 6.07 cm, with body fat of 14.7% ± 4.4% to complete our randomized crossover study. Participants were required to have previous equipment intensive sport experience. After a health history clearance and a familiarization session, participants completed two trials (once with and once without standard men’s lacrosse protective equipment) a simulated lacrosse exercise protocol consisting of four 12-minute sessions with rests totaling 60 minutes. Measured values included first morning urine osmolality and rating of perceived exertion (RPE), thermal sensation, thirst perception, and muscle pain perception every 15minutes throughout and following exercise. Results: There was no significant difference between trials with first morning urine osmolality (p=.128). In terms of equipment, RPE was significantly greater with equipment throughout trials (p\u3c.001) compared to the no equipment trial. Thermal sensation was significantly greater during the equipment trial versus the no equipment trial (p\u3c.001). Regardless of time point, thirst sensation was greater in the equipment trial compared to the no equipment trial (p=.001). Muscle pain was significantly greater throughout trials, regardless of time point (P=.006) in the equipment trial as well. Discussion: Overall, our study supported our hypothesis that men’s lacrosse equipment accentuates perceptual stress during exercise heat stress. Regardless of time point, RPE, thermal sensation, thirst sensation, and muscle pain were reported as greater during equipment trials than non-equipment trials. Funding Source: University of Arkansas Honors College Research Gran

Development of a versatile system for detailed studies of the performance of heat pipes

Heat pipe performance studies for space suit thermoregulation application

General dynamics of the physical-chemical systems in mammals

Human physiochemistry, thermoregulation, and harmonic oscillation of blood glucose level

Impaired thermoregulatory function during dynamic exercise in multiple sclerosis

INTRODUCTION: Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared to healthy controls (CON) exercising at similar rates of metabolic heat production. METHODS: Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass- and BSA-matched healthy controls during a single bout of cycling exercise (rate of metabolic heat production: ~4.5 W/kg) for 60 min in a climate-controlled room (25 °C, 30% RH). RESULTS: Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS: 72 ± 51; CON: 104 ± 37 g, p=0.04) and 60 min (MS: 209 ± 94; CON: 285 ± 62 g, p=0.02), as well as lower sweating thermosensitivity (MS: 0.49 ± 0.26; CON: 0.86 ± 0.30 mg/cm2/min/°C, p=0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30 or 60 min time points (p>0.05). Cutaneous vasculature responses were also not different in MS compared to CON (p>0.05). CONCLUSION: Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.Accepted manuscrip

Temperature discrimination, behavioral thermoregulation and related measures in the rat Final report

Hyperthermia, dietary, and desalivation effects on thermoregulation in rat