Effect of thermal stress on physiological parameters, feed intake and plasma thyroid hormones concentration in Alentejana, Mertolenga, Frisian and Limousine cattle breeds

The aim of the present study was to assess the heat tolerance of animals of two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds, through the monitoring of physiological acclimatization reactions in different thermal situations characterized by alternate periods of thermoneutrality and heat stress simulated in climatic chambers. In the experiment, six heifers of the Alentejana, Frisian and Mertolenga breeds and four heifers of the Limousine breed were used. The increase in chamber temperatures had different consequences on the animals of each breed. When submitted to heat stress, the Frisian animals developed high thermal polypnea (more than 105 breath movements per minute), which did not prevent an increase in the rectal temperature (from 38.7°C to 40.0°C). However, only a slight depression in food intake and in blood thyroid hormone concentrations was observed under thermal stressful conditions. Under the thermal stressful conditions, Limousine animals decreased food intake by 11.4% and blood triiodothyronine (T3) hormone concentration decreased to 76% of the level observed in thermoneutral conditions. Alentejana animals had similar reactions. The Mertolenga cattle exhibited the highest capacity for maintaining homeothermy: under heat stressful conditions, the mean thermal polypnea increased twofold, but mean rectal temperature did not increase. Mean food intake decreased by only 2% and mean T3 blood concentration was lowered to 85,6% of the concentration observed under thermoneutral conditions. These results lead to the conclusion that the Frisian animals had more difficulty in tolerating high temperatures, the Limousine and Alentejana ones had an intermediate difficulty, and the Mertolenga animals were by far the most heat tolerant.     

Tissue-specific localization of heat-stress proteins during embryo development

We report on the stress-independent, tissue-specific expression of the heat-stress protein HSP17 in developing seeds of different plant species and on its intracellular localization. Though HSP17 expression during seed development seems to be a general phenomenon, the isoform patterns, the relative amounts in embryonic tissues and the intracellular localization show species-specific variations. In contrast to the results on the stressinduced protein forming large cytoplasmic aggregates (heat stress granules) the developmentally expressed HSP17 is mainly found in nuclei. But in addition, a considerable part is also detected in protein bodies of mature seeds of Lycopersicon esculentum and Vicia faba, but not of Zea mays. The mechanism of this transition into the vacuolar compartment remains to be investigated.Abbreviations 2D two-dimensional - HSE heat shock elements - HSP heat stress protein     

Effects of cortisol administration on development of the thyroid and adrenal axes in rats

Intraperitoneal (IP) injections of cortisol were administered to neonatal male rats on postnatal days 1 to 4. Plasma triiodothyronine (T₃), thyroxine (T₄) and corticosteroids were determined on days 5, 10, 13, 16, 20, 30 and 60 of age, and all animals were weighed weekly. Neonatal cortisol treatment resulted in depressed body weight gain and transient depression in plasma T₄. These results indicate that while body weight is significantly affected by cortisol treatment ontogenic patterns of plasma T₃, T₄ and corticosteroids develop normally.     

Effects of early neonatal thyroxine treatment on development of the thyroid and adrenal axes in rats

Neonatal male rats were treated with intraperitoneal (IP) injections of thyroxine on postnatal days 1 to 4. Plasma triiodothyronine (T₃), thyroxine (T₄), and corticosteroids were determined on days 5, 10, 13, 16, 20, 30, and 60 of age, and all animals were weighed weekly. Neonatal thyroxine treatment resulted in reduced body weight throughout the entire test period, decreased T₃ and T₄ until day 60 of age, and elevated corticosteroids on days 5 to 13 of age. These results demonstrate that early neonatal T₄ treatment affects the ontogeny of both thyroid and adrenocortical hormones, and suggest that these developmental changes should be considered when evaluating the consequences of T₄ treatment during the early neonatal period.     

狭颅田鼠的代谢特征及体温调节

为探究草食性小型哺乳动物狭颅田鼠的代谢及体温特征,测定了栖息于呼伦贝尔草原地区的狭颅田鼠的体重、静止代谢率、热传导等生物学指标随环境温度的变化情况。结果表明:狭颅田鼠的平均体重为(20.8±0.8)g(n=12),基础代谢率为(1.85±0.05)mLO_2/(g·h),热中性区为27.5℃～35℃,热传导值为(0.19±0.03)mLO_2/(g·h·℃),热适应能力A<0(适应冷环境),适应途径指数I=0.8(热传导对调节体温影响更大)。狭颅田鼠具有低代谢率、低热传导和较宽的热中性区,在较大的温度变化范围内保持较低的能量代谢水平,这是生活于较高纬度寒冷地区的狭颅田鼠在长期进化过程中形成的主要生存对策之一。     

Repeated thermal conditioning during the neonatal period affects behavioral and physiological responses to acute heat stress in chicks

ObjectiveThe aim of the present study was to investigate the effects of repeated thermal conditioning (RTC) at an early age on physiological and behavioral responses in chicks.MethodsBirds were assigned to one of the four treatments in which the RTC was exposure to 40 °C for 15 min daily. The treatments were 1) no thermal conditioning (control); 2) early exposure group (EE; RTC from 2 to 4 days of age); 3) later exposure group (LE; RTC from 5 to 7 days of age); or 4) both early and later exposure (BE; RTC from 2 to 7 days of age). All groups of chicks were challenged with high ambient temperature (40 °C for 15 min) at two weeks of age.ResultsDuring heat challenge, initiation times of dissipation behaviors (panting and wing-drooping) were measured. Rectal temperature and respiration rate were measured after and before heat challenge. Hypothalamic samples and blood were collected at the end of heat challenges. Initiation times of dissipation behaviors and rectal temperature were not affected by the treatments. Increases in respiration rate in response to heat challenge were suppressed by early RTC treatment. There was no clear pattern of glucose levels in relation to thermal conditioning, whereas plasma corticosterone levels were decreased by early treatment (EE and BE groups). Hypothalamic thyrotropin releasing hormone gene expression was suppressed by early and later thermal conditioning and suppressed further by both early and later exposure. Neuropeptide Y gene expression in the BE group was lower than in the other groups, with a similar trend for corticotropin releasing hormone expression.ConclusionOur results suggest that the effect of repeated thermal conditioning on the central thermoregulatory system depends on the number of times that chicks experienced conditioning. In addition, repeated thermal conditioning has greater effects on the acquisition of thermotolerance when conditioning occurs in chicks of two to four days of age in comparison with chicks of five to seven days of age.     

Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat

New technologies afford convenient modalities for skin temperature (T_SKIN) measurement, notably involving wireless telemetry and non-contact infrared thermometry. The purpose of this study was to investigate the validity and reliability of skin temperature measurements using a telemetry thermistor system (TT) and thermal camera (TC) during exercise in a hot environment. Each system was compared against a certified thermocouple, measuring the surface temperature of a metal block in a thermostatically controlled waterbath. Fourteen recreational athletes completed two incremental running tests, separated by one week. Skin temperatures were measured simultaneously with TT and TC compared against a hard-wired thermistor system (HW) throughout rest and exercise. Post hoc calibration based on waterbath results displayed good validity for TT (mean bias [MB]=−0.18 °C, typical error [TE]=0.18 °C) and reliability (MB=−0.05 °C, TE=0.31 °C) throughout rest and exercise. Poor validity (MB=−1.4 °C, TE=0.35 °C) and reliability (MB=−0.65 °C, TE=0.52 °C) was observed for TC, suggesting it may be best suited to controlled, static situations. These findings indicate TT systems provide a convenient, valid and reliable alternative to HW, useful for measurements in the field where traditional methods may be impractical.     

Lack of effect of vasoactive intestinal peptide antagonists on blood flow in the rat thyroid

We used three putative vasoactive intestinal peptide (VIP) antagonists: 1) [4Cl-D-Phe⁶,Leu¹⁷]VIP, 2) [N-Ac-Tyr¹,D-Phe²]GRF(1–29)-NH₂, and 3) VIP(10–28) to assess the involvement of endogenous VIP in the regulation of thyroid hormone secretion and thyroid blood flow (BF). We measured thyroid BF in ketamine-pentobarbital-anesthetized rats using the microsphere technique. Increases in thyroid BF induced by VIP administration (30 pmol-1.5 nmol/100 g b.wt.) were not affected by any of the three compounds tested at doses 10–100 times higher than that of VIP. These compounds (3–15 nmol/100 g b.wt.) also failed to affect basal thyroid BF or hormone secretion. Increases in pancreatic and salivary gland BFs induced by VIP (30 pmol/100 g b.wt.) were also not affected by [4Cl-D-Phe⁶,Leu¹⁷]VIP or [N-Ac-Tyr¹,D-Phe²]GRF(1–29)-NH₂ (3 nmol/100 g b.wt.). These results indicate that the three compounds tested are not effective inhibitors of VIP receptors in the thyroid vasculature and, therefore, they cannot be used in the investigation of the functional significance of endogenous VIP in the regulation of thyroid BF.     

Effects of heat acclimatisation on work tolerance and thermoregulation in trained tropical natives

This study aimed to investigate the effects of heat acclimatisation on thermoregulatory responses and work tolerance in trained individuals residing in the tropics. Eighteen male trained soldiers, who are native to a warm and humid climate, performed a total of four heat stress tests donning the Skeletal Battle Order (SBO, 20.5 kg) and Full Battle Order (FBO, 24.7 kg) before (PRE) and after (POST) a 10-day heat acclimatisation programme. The trials were conducted in an environmental chamber (dry bulb temperature: 32 °C, relative humidity: 70%, solar radiation: 400 W/m²). Excluding the data sets of which participants fully completed the heat stress tests (210 min) before and after heat acclimatisation, work tolerance was improved from 173±30 to 201±18 min (∼21%, p<0.05, n=9) following heat acclimatisation. Following heat acclimatisation, chest skin temperature during exercise was lowered in SBO (PRE=36.7±0.3 vs. POST=36.5±0.3 °C, p<0.01) and FBO (PRE=36.8±0.4 vs. POST=36.6±0.3 °C, p<0.01). Ratings of perceived exertion were decreased with SBO and FBO (PRE=11±2; POST=10±2; p<0.05) after heat acclimatisation. Heat acclimatisation had no effects on baseline body core temperature, heart rate and sweat rate across trials (p>0.05). A heat acclimatisation programme improves work tolerance with minimal effects on thermoregulation in trained tropical natives.     

Validation of the effect of helox on thermal conductance in homeotherms using heated models

It is commonly stated that mixtures of 80% helium and 20% oxygen (helox) increase thermal conductance, and hence heat flux, from homeotherms by roughly a factor of two. However, because helox affects heat loss by conduction and convection differently, its effect on heat flux should vary according to the relative contributions of these two routes to the overall heat flux. We used heated models made of three sizes of copper tubing and covered with various grades of synthetic fur to measure heat flux under air and helox atmospheres. Thermal conductance in helox (C_helox; W•m⁻² •°C⁻¹) was highly correlated with thermal conductance in air (C_air) and could be predicted by C_helox=1.704+1.726 C_air. The relative increase in heat flux under a helox atmosphere compared with that in air (conductance ratio; C_helox/C_air) varied from a maximum of 2.5 when thermal conductance is infinitely small and heat flux is predominantly determined by conduction to a minimum of 1.85 when animals are naked and heat flux is dominated by convection. These values follow the relation: C_helox/C_air=2.503−0.081 C_air. Body size has no significant effect on the conductance ratio.     

Differential effect of triiodothyronine and thyroxine on the liposomal membrane in liquid-crystalline and gel state

The effect of thyroid hormones on the degree of order or fluidity of dimyristoyl, dipalmitoyl or egg yolk phosphatidyl choline liposomes was evaluated by fluorescence spectroscopy methods. The freedom of molecular motion above the phase transition temperature was decreased, while below the transition, the mobility was actually increased by the incorporation of triiodothyronine to liposomes. While thyroxine decreases the fluidity in the liquid crystalline state, it cannot increase the fluidity in the gel state.A differential effect of triiodothyronine and thyroxine on the release of the liposomal content was found, depending on the liquid crystalline or gel state of the liposomes. These facts were correlated with the differential incorporation of the hormones to liposomes above and below the phase transition temperature of dimyristoyl and dipalmitoyl phospholipid choline. In gel state, a low incorporation of thyroxine compared with triiodothyronine was found.This work was supported by Grants PID 3-013800/89 from Consejo National de Investigaciones Científicas y Técnicas (CONICET), Fundación Antorchas A-12576/1-000065 and Consejo de Investigaciones de la Universidad National de Tucumán (CIUNT). We thank Dr. G. Rotillo for the space filling models.     

Effects of cold- and heat hardening on thermal resistance in Drosophila melanogaster

The effects of cold- and heat hardening on resistance to both low and high temperature stress was examined in Drosophila melanogaster lines selected for resistance to either cold or heat. The hardening effect was positive when the hardening was of the same type as the stress in all selection regimes. The effect of cold hardening on survival after heat stress was further examined in the lines selected for cold resistance and corresponding controls. A cross-protection effect (increased heat resistance after cold hardening) was present and this effect was lower in the lines selected for resistance to cold than in the controls. The level of Hsp70 expression induced by a non-lethal cold hardening was examined, showing that cold hardening induced Hsp70 expression. The results suggest that the cross-protection effect is at least partly due to Hsp70 expression induced by cold exposure.     

Exploring the role of copper and selenium in the maintenance of normal thyroid function among healthy Koreans

BackgroundSelenium and iodine are trace elements well known to have important roles in the synthesis and metabolism of thyroid hormones. However, the effects of other trace elements on thyroid hormones are still inconclusive. We investigated the association between several trace elements and thyroid hormones.MethodsThe data of 448 subjects who were measured for both, trace elements and TSH/free T4, at the Heath Checkup Center were retrospectively reviewed. The presence of thyroiditis (from thyroid echogenicity) and thyroid nodules were reviewed in the subjects who underwent thyroid ultrasonography.ResultsBlood concentrations of manganese, copper, selenium, and molybdenum were associated with TSH or free T4. After adjusting for age, sex, BMI, smoking, and alcohol consumption, blood copper levels were positively associated with free T4 in both sexes and selenium levels were positively associated with free T4 in women. There was no association between trace elements and thyroiditis. Blood copper concentration had a weak non-linear association with the presence of thyroid nodules.ConclusionsThis study demonstrated that blood concentrations of copper and selenium were significantly associated with free T4 in healthy Korean subjects with sufficient iodine intake suggesting their role in maintaining normal thyroid function.     

The impact of insularity on the thermoregulation of a Mediterranean lizard

The overall biology of ectotherms is strongly affected by the thermal quality of the environment. The particular conditions prevailing on islands have a strong effect on numerous features of animal life. In this study we compared mainland and island populations of the lizard Lacerta trilineata and hypothesized that insularity would affect the thermoregulatory strategy. Continental habitats were of lower thermal quality, experiencing more intense fluctuations and had higher values of operative temperatures. Nevertheless mainland lizards selected for higher body temperatures in the lab and showed more effective thermoregulation during summer than their island peers. Lizards achieved similar body temperatures in the field in both types of habitat, underlining the importance of predation as a potential factor to mainland lizards that failed to reach their higher thermal preferences. Both island and mainland populations of L. trilineata have been adapted to their thermal environment, supporting the labile view on the evolution of thermal physiology for this species.     

Influence of varying sources of dietary electrolytes on the performance of broilers reared in a high temperature environment

Experiment using 297 broiler chicks, kept from 1 to 42 days under cyclic heat stress (minimum 29.3 °C and maximum 38 °C), was conducted to investigate the relative efficacies of three sodium (NaHCO₃, Na₂CO₃, Na₂SO₄), and potassium (KHCO₃, K₂CO₃, K₂SO₄) supplements at an identical dietary electrolyte balance (DEB) 250 mEq/kg and two chloride supplements (CaCl₂ and NH₄Cl) at DEB 50 mEq/kg. The desired levels of DEB were achieved by substitution of individual mineral supplement at the expense to builder's sand in the basal starter (DEB 185.6 mEq/kg) and finisher (DEB 174 mEq/kg) diet containing only salt as a source of Na and Cl. Each diet (one basal and eight experimental) was fed to three experimental units having 11 chicks each. The growth performances in K supplements, except KHCO₃, were poorer than those of Na supplements. The NaHCO₃, Na₂CO₃, Na₂SO₄ and NH₄Cl increased body weight gain, feed intake and improved feed to gain ratio than those of K₂CO₃ and K₂SO₄ after 42 days of age. These supplements also increased the water intake and resulted in lowered body temperature as well as reduced mortality. Very poor performance in CaCl₂ supplement was associated with disturbed calcium:phosphorus and very low blood pH (7.19). Better performance was noted with bicarbonate than that with carbonate and sulfate sources. The KHCO₃ accentuate the respiratory alkalosis by increasing blood HCO₃ contents (26.09 mmol/l) and gave poorer performance than NaHCO₃. Blood lymphocytes, hemoglobin, hematocrit and electrolyte balance in heat stressed broilers were better improved by NH₄Cl, NaHCO₃, Na₂CO₃, Na₂SO₄ and KHCO₃ than those of CaCl₂, K₂CO₃ and K₂SO₄ supplements. Present findings emphasized the importance of considering metabolisable anions supplemented in association with cations while balancing the dietary electrolyte equations. That is why DEB equation cannot be used to predict the relative benefits of different mineral supplements.     

Identification and expression analysis of four heat shock protein genes associated with thermal stress in rice weevil, Sitophilus oryzae

In order to explore the function of heat shock proteins during thermal stress in rice weevil, Sitophilus oryzae, four heat shock protein genes were cloned and characterized. These heat shock protein genes (hsps) were named as Sohsp70–1, Sohsp70–2, Sohsc70, and Sohsp90, respectively. These hsps showed high sequence conservation with the maximum identity with hsps of Tribolium castaneum and other insects. All the four genes showed the highest mRNA expression in pupal stage and the lowest levels in larval stage. The induced expression of the two Sohsp70s (Sohsp70–1 and Sohsp70–2) were reached to the highest levels (15.59-fold and 12.66-fold) after 2?h of incubation at 37?°C, respectively. Expression of Sohsp90 not only was significantly elevated by heat stress but also by cold stress. Whereas, expression level of Sohsc70 was not induced either by heat or cold stress. Furthermore, for rapid heat hardening, the expression levels of Sohsp70–1, Sohsp70–2, Sohsc70 and Sohsp90 were observed as 2.57, 2.53, 3.33 and 2.33-fold higher than control, respectively; for rapid cold hardening, the expression levels of Sohsp70–1, Sohsp70–2, Sohsc70 and Sohsp90 were reported as 2.27, 3.02, 3.37 and 2.23-fold higher than control, respectively. Hence, our results revealed that the four Sohsps were associated with temperature adaption under rapid heat or cold hardening.     

The effect of body size on the thermoregulation of lizards on hot,dry Mediterranean islands

Body size shapes the overall biology of organisms. We assessed the impact of size on temperature regulation in populations of normal-sized and large-bodied insular Mediterranean lizards (Podarcis gaigeae, Lacertidae). We hypothesized that large lizards would achieve higher body temperatures and thermoregulate more effectively than their smaller kin. Large- and small-bodied lizards share the same thermoregulation pattern, achieving similar body temperatures in the field. Large lizards, however, prefer higher set-point temperatures. Lizards in both populations thermoregulate effectively, but large lizards thermoregulated less effectively than normal-sized lizards. The particular conditions at the islet that harbors the large-bodied population (harsh intraspecific competition) seem to account for this pattern.     

Differential effect of triiodothyronine and thyroxine on liposomes containing cholesterol: Physiological speculations

The effect of thyroid hormones on the steadystate fluorescence polarization and on the release of the liposomal content was analyzed in liposomes composed of egg phosphatidylcholine and egg phosphatidyl choline: cholesterol in different molar ratios. Depending on liposome cholesterol composition, a dual effect of triiodothyronine was found. The fluorescence polarization of 1,6 diphenyl 1,3,5 hexatriene or 1-(4-trimethylaminophenyl) 6 phenyl-1, 3, 5 hexatriene decreased by the addition of the hormone when cholesterol content was in the range from 0 to 30 moles %, while it increased with cholesterol from 30 to 50 moles %. In the release experiments, the effect of triiodothyronine was also biphasie; the leakage was the highest at 0% and 50% and the lowest at 30 moles % of cholesterol. On the contrary, thyroxine was without effect on liposomes containing cholesterol from 30 to 50 mol %. This fact correlated with a lower incorporation of thyroxine, compared with that of triiodothyronine in liposomes containing up to 30 moles % of cholesterol.The fact that the above differential incorporation of thyroid hormones was also observed at physiological concentration and that most of the mammalian membrane cells have more than 25 moles % of cholesterol have for physiological implications to the observations reported here.     

Effect of serum estradiol and leptin levels on thyroid function, food intake and body weight gain in female Wistar rats

We evaluated the interplay among estrogen, leptin and thyroid function in the regulation of body mass in female rats. Adult female rats were divided into four groups: control (C, sham-operated), ovariectomized (OVX), ovariectomized treated with estradiol benzoate (Eb) 0.7 or 14 μg/100 g bw per day, during 21 days. OVX led to an increase in body mass, food intake and food efficiency (change in body mass as function of the amount of food ingested) which were normalized by the lower Eb dose, and decreased significantly when the higher dose was given. Serum leptin levels were increased more than two-fold in all ovariectomized groups. Serum T4 levels of the Eb treated OVX were significantly lower than in the controls. Serum T3 and TSH were unaffected by OVX or by Eb treatment. Uterine type 2 iodothyronine deiodinase (D2) activity changed in parallel with serum estradiol: decreased after OVX, returned to control levels after the lower E2 treatment, and increased significantly after the high Eb dosage. The hypothalamic D2 activity was reduced around 30% in all castrated groups, treated or not with estrogen, whereas in the brown adipose tissue the enzyme was not changed. Interestingly, although estrogen-treated OVX rats had lower body weight, serum leptin was high, suggesting that estrogen increases leptin secretion. Our results show that estradiol is necessary for the hypothalamic action of leptin, since the increase in leptin levels observed in all ovariectomized rats was associated with a decrease in food intake and food efficiency only in the rats treated with estrogen.     

Living in sympatry: The effect of habitat partitioning on the thermoregulation of three Mediterranean lizards

The ability for effective, accurate and precise thermoregulation is of paramount importance for ectotherms. Sympatric lizards often partition their niche and select different microhabitats. These microhabitats, however, usually differ in their thermal conditions and lizards have to adapt their thermoregulation behavior accordingly. Here, we evaluated the impact of habitat partitioning on the thermal biology of three syntopic, congeneric lacertids (Podarcis peloponnesiacus, P. tauricus and P. muralis) from central Peloponnese, Greece. We assessed thermoregulation effectiveness (E) using the three standard thermal parameters: body (T_b), operative (T_e) and preferred (T_pref) temperatures. We hypothesized that the microhabitats used by each species would differ in thermal quality. We also predicted that all species would effectively thermoregulate, as they inhabit a thermally challenging mountain habitat. As expected, the partition of the habitat had an effect on the thermoregulation of lizards since microhabitats had different thermal qualities. All three species were effective and accurate thermoregulators but one of them achieved smaller E values as a result of the lower T_b in the field. This discrepancy could be attributed to the cooler (but more benign) thermal microhabitats that this species occupies.