scholarly journals Comparison of heat and cold stress to assess thermoregulatory dysfunction in hypothyroid rats

2000 ◽  
Vol 279 (6) ◽  
pp. R2066-R2071 ◽  
Author(s):  
Christopher J. Gordon ◽  
Peggy Becker ◽  
Beth Padnos
Keyword(s):  
Heat Stress ◽  
Cold Stress ◽  
Serum Levels ◽  
Thyroid Stimulating Hormone ◽  
Overt Hypothyroidism ◽  
Environmental Toxicants ◽  
Thermoregulatory Response ◽  
Light Phase ◽  
Treatment Groups ◽  
Heat And Cold Stress

How borderline impairment of thyroid function can affect thermoregulation is an important issue because of the antithyroidal properties of a many environmental toxicants. This study compared the efficacy of heat and cold stress to identify thermoregulatory deficits in rats subjected to borderline and overt hypothyroidism via subchronic exposure to propylthiouracil (PTU). After 3 wk of exposure to PTU in the drinking water (0, 2.5, 5, 10, and 25 mg/l), rats were subjected to a heat stress challenge (34°C for 2.5 h). After one more week of PTU treatment, the same rats were subjected to a cold stress challenge (7°C for 2.5 h). Core temperature (Tc) was monitored by radiotelemetry. Baseline Tc during the light phase was reduced by treatment with 25 mg/l PTU. The rate of rise and overall increase in Tcduring heat stress was attenuated by PTU doses of 10 and 25 mg/l. Cold stress resulted in a 1.0°C increase in Tc regardless of PTU treatment. The rate of rise in Tc during the cold stress challenge was similar in all PTU treatment groups. There was a dose-related decrease in serum thyroxine (T4) at PTU doses ≥5 mg/l. Serum triiodothyronine (T3) was reduced at PTU doses of 5 and 25 mg/l. Serum thyroid-stimulating hormone (TSH) was marginally elevated by PTU treatment. Overall, heat stress was more effective than cold stress for detecting a thermoregulatory deficit in borderline (i.e., 10 mg/l PTU) and overtly hypothyroid rats (i.e., 25 mg/l PTU). A significant thermoregulatory deficit is manifested with a 78% decrease in serum T4. A thermoregulatory deficit is more correlated with a reduction in serum T4 compared with T3. Serum levels of TSH are unrelated to thermoregulatory response to heat and cold stress.

Regulated hypothermia in the hypothyroid rat induced by administration of propylthiouracil

1997 ◽  
Vol 272 (5) ◽  
pp. R1390-R1395 ◽  
Author(s):  
Y. Yang ◽  
C. J. Gordon
Keyword(s):  
Drinking Water ◽  
Heat Stress ◽  
Temperature Gradient ◽  
Serum Levels ◽  
Male Rats ◽  
Light Phase ◽  
Grooming Behavior ◽  
Ambient Temperatures ◽  
Wide Range ◽  
The Stability

Propylthiouracil (PTU), an antithyroidal drug that reduces serum L-thyroxine (T4) and 3,5,3'-triiodothyronine (T3), is presumed to lower core temperature (T0) by impairing metabolic thermogenesis. However, it is not understood why PTU-treated animals cannot use behavioral and other thermoeffectors to maintain normal Tc. Male rats were administered PTU in drinking water (0.05 mg/ml) while the following parameters were measured: 1) Tc and motor activity (MA) recorded by radiotelemetry for 24 h at ambient temperatures (Ta) of 10-30 degrees C; 2) selected Ta, MA, and Tc in a temperature gradient; and 3) Tc, MA, and grooming behavior during exposure to heat stress (TH = 34.5 degrees C) for 2 h. PTU reduced serum levels of T4, and T3 by 95 and 60%, respectively. Tc decreased after 3 days of PTU treatment; a 0.5 degree C decrease in Tc persisted throughout the PTU treatment. PTU rats exposed to Ta of 10-30 degrees C maintained a consistent hypothermic Tc during the light phase; however, a deficit in the stability of Tc at night was noted during exposure to 10 degrees C. In the temperature gradient, PTU rats selected warmer Ta, but their Tc was maintained at the same hypothermic levels as observed at fixed Ta values of 15-30 degrees C. Heat stress caused Tc of control rats to increase to 39 degrees C, whereas Tc of the PTU rats was maintained below 38 degrees C. The regulation of Tc at hypothermic levels over a wide range of Ta values and when rats were housed in a temperature gradient indicates that chronic PTU induces a state of regulated hypothermia.

scholarly journals The Effect of Vitamin D Replacement on Patient with Subclinical Hypothyroidism: A Pilot Randomized Clinical Trial

2020 ◽  
Vol 9 ◽  
pp. 1592
Author(s):  
Babak Pezeshki ◽  
Ali Ahmadi ◽  
Aliasghar Karimi
Keyword(s):  
Vitamin D ◽  
Vitamin D Deficiency ◽  
Subclinical Hypothyroidism ◽  
Serum Levels ◽  
Thyroid Stimulating Hormone ◽  
T Test ◽  
Overt Hypothyroidism ◽  
Paired Samples ◽  
The Difference ◽  
Vitamin D Supplements

Background: Subclinical hypothyroidism (SCH) is characterized by an elevated Thyroid Stimulating Hormone (TSH) with a normal T4. The prevalence of Vitamin D deficiency in patients SCH is high. Some studies suggested that Vitamin D supplements could be reduced serum concentration of TSH so improve SCH and prevent overt hypothyroidism. This study aims to explore the effect of vitamin D replacement on subclinical hypothyroidism. Materials and Methods: Fifty-nine patients, diagnosed with both subclinical hypothyroidism and Vitamin D deficiency by the Endocrinology outpatient clinics between January 2018 and March 2019, were included in this trial. The patients with overt hypothyroidism, cardiovascular risk factors, or positive TPO antibody, abnormal T4, and pregnant women were excluded from this study. The 40 subjects were investigated who received vitamin D supplements for two months.  Analyses were conducted through paired-samples t-test and independent-samples t-test using SPSS 24 (Armonk, NY: IBM Corp). Results: The mean serum levels of TSH was decreased from 6.89 mIU/l in the pre-test to 3.34 mIU/l in the post-test, and the difference was found to be statistically significant at P<0.001. Conclusion: We found that the TSH mean level significantly dropped through the use of vitamin D supplements. Thus, it is recommended that all the patients with subclinical hypothyroidism be screened and treated with vitamin D supplements. [GMJ.2020;9:e1592]

Aging and the skin blood flow response to the unloading of baroreceptors during heat and cold stress

2004 ◽  
Vol 96 (3) ◽  
pp. 1019-1025 ◽  
Author(s):  
Glaucio Scremin ◽  
W. Larry Kenney
Keyword(s):  
Blood Flow ◽  
Heat Stress ◽  
Cold Stress ◽  
Skin Blood Flow ◽  
Forearm Blood Flow ◽  
Lower Body Negative Pressure ◽  
Older Men ◽  
Stress Conditions ◽  
Vascular Conductance ◽  
Heat And Cold Stress

Control of skin blood flow (SkBF) is on the efferent arm of both thermoregulatory and nonthermoregulatory reflexes. To what extent aging may affect the SkBF response when these two reflex systems interact is unknown. To determine the response of aged skin to the unloading of baroreceptors in thermoneutral, cold stress, and heat stress conditions, sequential bouts of nonhypotensive lower body negative pressure (LBNP) were applied at -10, -20, and -30 mmHg in 14 young (18–25 yr) and 14 older (63–78 yr) men. SkBF was measured by laser-Doppler velocimetry (averaged over 2 forearm sites), and data are expressed as percentage of maximal cutaneous vascular conductance (%CVCmax). Total forearm blood flow was measured by venous occlusion plethysmography, and forearm vascular conductance (FVC) was calculated as the ratio of forearm blood flow to mean arterial pressure. In young men, all three intensities of LBNP in thermoneutrality decreased FVC significantly ( P < 0.05), but FVC at -10 mmHg did not change in the older men. There were no significant LBNP effects on %CVCmax. Application of LBNP during cold stress did not significantly change %CVCmax or FVC in either age group. During heat stress, -10 to -30 mmHg of LBNP decreased FVC significantly ( P < 0.05) in both age groups, but these decreases were attenuated in the older men ( P < 0.05). %CVCmax decreased at -30 mmHg in the younger men only. These results suggest that older men have an attenuated skin vasoconstrictor response to the unloading of baroreceptors in heat stress conditions. Furthermore, the forearm vasoconstriction elicited by LBNP in older men reflects that of underlying tissue (i.e., muscle) rather than that of skin, whereas -30 mmHg LBNP also decreases SkBF in young hyperthermic men.

scholarly journals Investigating the prevalence of primary thyroid dysfunction in obese and overweight individuals: Tehran thyroid study

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Mahdi Mahdavi ◽  
Atieh Amouzegar ◽  
Ladan Mehran ◽  
Elham Madreseh ◽  
Maryam Tohidi ◽  
...  
Keyword(s):  
Serum Levels ◽  
Thyroid Stimulating Hormone ◽  
Normal Weight ◽  
Control Group ◽  
Overt Hypothyroidism ◽  
Thyroid Peroxidase ◽  
Cross Sectional ◽  
Increased Risk ◽  
Prevalence Of Obesity ◽  
Thyroid Dysfunctions

Abstract Background Due to the increasing worldwide prevalence of obesity, it is essential to determine the prevalence of obesity-related thyroid dysfunctions. The purpose of this study was to investigate the prevalence of thyroid dysfunctions, namely hypothyroidism and hyperthyroidism, and their association with BMI among adult Iranian overweight and obese individuals. Method This cross-sectional study was carried out within the framework of the Tehran Thyroid Study (TTS); 5353 participants (57.5% female) entered our study. Anthropometric measurements were performed. Serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid peroxidase antibody (TPOAb) were assayed. We categorized individuals into 3 BMI groups (normal-weight, overweight and obese), then calculated prevalence rate, odds ratio (OR), and 95% confidence interval (CI) for outcomes in overweight and obese groups. The normal-weight group was used as the control group. Results We found a higher prevalence of hypothyroidism (11.6% vs 8.2% Total, 4.0% vs 1.1% overt and 7.6% vs 7.1% subclinical, P < 0.001) and TPOAb positivity (17.3% vs 11.6%, P < 0.001) in obese participants compared with normal-weight participants. Hyperthyroidism’s overall prevalence was 4.2, 5.7, and 4.9% in obese, overweight, and normal-weight groups, respectively. Obesity was associated with higher odds of overt hypothyroidism (OR: 2.0, 95% CI: 1.15–3.49, P < 0.05) and TPOAb positivity (OR: 1.29, 95% CI: 1.04–1.60, P < 0.05) after adjusting for confounding variables. In contrast, no association was observed between the overweight group and the odds of hypothyroidism and TPOAb positivity in the adjusted results. Conclusions Obesity was associated with an increased risk of overt hypothyroidism and TPOAb positivity.

scholarly journals The assessment of human bioclimate of Vranje health resort (Serbia) based on Universal Thermal Climate Index (UTCI) with the focus on extreme biothermal conditions

2021 ◽  
Vol 94 (2) ◽  
pp. 201-222
Author(s):  
Milica Pecelj ◽  
Anna Błażejczyk ◽  
Nemanja Vagić ◽  
Peca Ivanović
Keyword(s):  
Heat Stress ◽  
Thermal Stress ◽  
Cold Stress ◽  
Weather Data ◽  
Climate Index ◽  
Universal Thermal Climate Index ◽  
Heat And Cold Stress ◽  
Thermal Climate ◽  
Extreme Cold ◽  
Bioclimatic Conditions

The study deals with an assessment and interpretation of the bioclimatic conditions in Vranje (southern Serbia). The study aims at temporal distributions of bioclimatic conditions focussing on extreme thermal stress based on the Universal Thermal Climate Index (UTCI). The meteorological data required for the calculation of UTCI concern hourly (7 and 14 CET) weather data collected for the period 2000-2017. The frequency of very strong heat stress (VSHS), very strong cold stress (VSCS) and extreme cold stress (ECS) for both morning and midday hours. Furthermore, the daily difference of the UTCI hourly values (diurnal UTCI change) are specified, giving the daily variance of heat and cold stress. The results revealed the frequency of days in which thermal stress prevails for the studied period. The obtained results show an increase in extreme heat biothermal conditions, while extreme cold biothermal conditions are in decline, especially in the last 10 years. However, the frequency (the number of days) of very strong heat stress (VSHS) increased since 2007. A spectacular increase in heat stress was observed in the month of September, particularly in 2015.

scholarly journals What is the most threatening for citizens of a mid-latitude city: cold stress or heat stress?

2021 ◽  
Author(s):  
Sara Top ◽  
Dragan Milošević ◽  
Steven Caluwaerts ◽  
Stevan Savić
Keyword(s):  
Heat Stress ◽  
Cold Stress ◽  
Thermal Comfort ◽  
Heat Wave ◽  
Outdoor Thermal Comfort ◽  
Belgian Society ◽  
Human Thermal Comfort ◽  
Summer Heat ◽  
Heat And Cold Stress ◽  
The City

&lt;p&gt;Both heat and cold waves cause extreme human thermal discomfort and a clear excess in mortality. This shows the importance of knowing the prevailing thermal comfort conditions and how thermal comfort conditions vary in various environments so measures can be taken. Microclimatic and outdoor human thermal comfort conditions are investigated in various built-up and green areas in the city of Ghent (Belgium) using meteorological measurements of six weather stations of the MOCCA (Monitoring the Cities Climate and Atmosphere) network in combination with calculations done by RayMan.&lt;/p&gt;&lt;p&gt;Normal to extreme summer heat wave periods show that dangerous strong heat stress prevails during the daytime periods at all locations. Comparison of thermal comfort during normal and extreme summer heat wave periods showed that heat stress is more extreme when a heat wave is more intense. Overall the urban park in Ghent was the most comfortable location during heat waves since it effectively mitigates heat stress in the city. These results should be taken into account in urban planning and design to keep mid-latitude cities livable.&lt;/p&gt;&lt;p&gt;Further, a one year data series revealed that outdoor cold stress was more apparent during 2017 in the mid-latitude city of Ghent that experiences a mild maritime climate. During spring and summer, both heat stress and cold stress occurred due to the larger diurnal temperature range compared to the other seasons. Even though high Physiological Equivalent Temperatures (PET) were obtained during a heat wave in summer, heat stress did not occur as intensely and as frequently compared to cold stress on annual level. It could thus be stated that outdoors, cold stress is a bigger threat than heat stress. However, one should keep in mind that the study was executed for outdoor thermal heat comfort and that people will take shelter or take measures when feeling uncomfortable. The question is thus rather, how are citizens protected against heat and cold stress? Currently, the Belgian society is better adapted to cold stress since most buildings contain central heating, while air conditioning is not standard. Future projections predict an increase in temperature, causing more occurrence of extreme heat stress, while extreme cold stress will be reduced. Additionally, the urban heat island effect currently has mainly a positive effect on the average annual outdoor thermal comfort conditions, while it will become a negative effect in the warmer future. Measures should thus be taken to reduce the threat of future heat stress.&lt;/p&gt;

scholarly journals Effects of heat and cold on health, with special reference to Finnish sauna bathing

2018 ◽  
Vol 314 (5) ◽  
pp. R629-R638 ◽  
Author(s):  
Ilkka Heinonen ◽  
Jari A. Laukkanen
Keyword(s):  
Heat Stress ◽  
Cold Stress ◽  
Human Health ◽  
Cardiovascular Health ◽  
Disease Risk ◽  
Heat Exposure ◽  
Beneficial Effects ◽  
Cold Environments ◽  
Heat And Cold Stress ◽  
Sauna Bathing

Environmental stress such as extremely warm or cold temperature is often considered a challenge to human health and body homeostasis. However, the human body can adapt relatively well to heat and cold environments, and recent studies have also elucidated that particularly heat stress might be even highly beneficial for human health. Consequently, the aim of the present brief review is first to discuss general cardiovascular and other responses to acute heat stress, followed by a review of beneficial effects of Finnish sauna bathing on general and cardiovascular health and mortality as well as dementia and Alzheimer's disease risk. Plausible mechanisms included are improved endothelial and microvascular function, reduced blood pressure and arterial stiffness, and possibly increased angiogenesis in humans, which are likely to mediate the health benefits of sauna bathing. In addition to heat exposure with physiological adaptations, cold stress-induced physiological responses and brown fat activation on health are also discussed. This is important to take into consideration, as sauna bathing is frequently associated with cooling periods in cold(er) environments, but their combination remains poorly investigated. We finally propose, therefore, that possible additive effects of heat- and cold-stress-induced adaptations and effects on health would be worthy of further investigation.

scholarly journals Long-term changes in hazardous heat and cold stress in humans: multi-city study in Poland

2021 ◽  
Author(s):  
Magdalena Kuchcik ◽  
Krzysztof Błażejczyk ◽  
Agnieszka Halaś
Keyword(s):  
Heat Stress ◽  
Cold Stress ◽  
Stress Conditions ◽  
Climate Index ◽  
Temporal And Spatial Distribution ◽  
Climate Conditions ◽  
North East ◽  
Heat And Cold Stress ◽  
Winter Time ◽  
Summer Time

AbstractSignificant changes in climate variables in the last decades resulted in changes of perceived climate conditions. However, there are only few studies discussing long-lasting changes in bioclimatic conditions. Thus, the purpose of this paper is to present the temporal and spatial distribution of hazardous heat and cold stress conditions in different regions of Poland. Its focus is on long-lasting changes in such conditions in the period 1951–2018. To assess changes in hazardous thermal stress conditions, the Universal Thermal Climate Index (UTCI) was used. UTCI values at 12 UTC hour (respectively 1 pm winter time, 2 pm summer time) were calculated daily based on air temperature, relative humidity, total cloud cover and wind speed at 24 stations representing the whole area of Poland. We found that the greatest changes were observed in minimum (1.33 °C/10 years) and average (0.52 °C/10 years) UTCI values as well as in cold stress frequency (− 4.00 days per 10 years). The changes vary seasonally and regionally. The greatest increase in UTCImin and decrease in cold stress days were noted from November to March and had the highest values in north-east and east Poland, and also in the foothills of the Carpathian Mountains. The trends in maximum UTCI are much smaller and not always positive. The spatially averaged trend in UTCImax for Poland as a whole was 0.35 °C/10 years and the increase in heat stress days was 0.80 days/10 years. The highest increases in UTCImax and heat stress days were noted in eastern and south-eastern Poland.

Heat and cold stress in the Antarctic

Polar Record ◽  
1976 ◽  
Vol 18 (113) ◽  
pp. 143-149 ◽  
Author(s):  
Denis Wilkins
Keyword(s):  
Heat Stress ◽  
Cold Stress ◽  
Heat Loss ◽  
Repeated Exposure ◽  
Strenuous Exercise ◽  
Conflicting Evidence ◽  
Heat And Cold Stress ◽  
Heat Conservation ◽  
Research Facilities ◽  
The Antarctic

It has long been supposed that repeated exposure of a man to cold conditions might be expected to produce changes within him which would better enable him to stand up to those cold conditionsto acclimatize to cold. Until recently, however, there has been little and conflicting evidence of the mechanism of such changes. Accounts of the polar explorers of the Scott-Amundsen era reveal that these men were exposed to severe cold stresses, but unfortunately the sophisticated research facilities necessary to measure the various factors involved were not then available. Now that these facilities are available, man conducts his polar activities under far more comfortable conditions, and the degree of cold stress to which he is exposed is probably of a much smaller order. Small wonder, then, that research into the elusive phenomenon of acclimatization to cold has yielded little profit. In fact, the available evidence suggests that the polar traveller may well undergo a marked heat stress as a result of strenuous exercise under conditions in which he is unable to get rid of surplus heat easily. This article looks at the basic physiological problems of heat loss and heat conservation with which the modern polar traveller has to contend, and points out the results of some recent investigations.

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