THERMOREGULATORY EFFECT IN HUMANS OF SUPPRESSED ENDOGENOUS MELATONIN BY PRE-SLEEP BRIGHT-LIGHT EXPOSURE IN A COLD ENVIRONMENT

This study investigated the physiological function of suppressed melatonin through thermoregulation in a cold environment. Interactions between thermoregulation directly affected by exposure to a cold environment and indirectly affected by endogenous melatonin suppression by bright-light exposure were examined. Ten male subjects were exposed to two different illumination intensities (30 and 5000 lux) for 4.5?h, and two different ambient temperatures (15 and 27°C) for 2?h before sleep under dark and thermoneutral conditions. Salivary melatonin level was suppressed by bright light (p?<?0.001), although the ambient temperature condition had no significant effect on melatonin. During sleep, significant effects of pre-sleep exposure to a cold ambient temperature (p?<?0.001) and bright light (p?<?0.01) on rectal temperature (T_re) were observed. Pre-sleep, bright-light exposure led to an attenuated fall in T_re during sleep. Moreover, T_re dropped more precipitously after cold exposure than thermoneutral conditions (cold: ?0.54?±?0.07°C/h; thermoneutral: ?0.16?±?0.03°C/h; p?<?0.001). Pre-sleep, bright-light exposure delayed the nadir time of T_re under thermoneutral conditions (p?<?0.05), while cold exposure masked the circadian rhythm with a precipitous decrease in T_re. A significant correlation between the T_re nadir and melatonin level (r?=??0.774, p?<?0.05) indicated that inter-individual differences with higher melatonin levels lead to a reduction in T_re after cold exposure. These results suggest that suppressed endogenous melatonin inhibits the downregulation of the body temperature set-point during sleep. (Author correspondence: ishibasi@design.kyushu-u.ac.jp)     

Effects of simulated natural air movement on thermoregulatory response during head-down bed rest

Spaceflight and its bed rest analog impair thermoregulatory responses, including elevated core temperature observed at rest and during exercise. Natural air flow has been found to increase cold sensation significantly compared to artificial constant air flow (CAF). The present study tested the hypothesis that simulated natural air flow (SNAF) ventilation would ameliorate impaired thermoregulatory function to a greater extent than CAF under simulated microgravity conditions. Seven healthy males underwent 30 days of −6° head-down bed rest (HDBR). During pre-HDBR and the day 29 of HDBR (HDBR 29), the subjects were exposed to three air flow patterns at 23 °C while in a supine posture: a still air flow control (CON), CAF, and SNAF. The mean air velocity of the latter two patterns was 0.2 m/s. Subjective perception of the thermal environment was recorded by thermal sensation vote (TSV), and rectal temperature (T_re), skin temperature (T_sk), and cutaneous vascular conductance (CVC) were also measured during the sessions. T_re was significantly elevated after 29 days of HDBR and decreased to a greater extent in SNAF than in CAF on HDBR 29. However, there was no significant difference between T_re in SNAF on HDBR 29 and that in CON on pre-HDBR. Mean T_sk, CVC, and TSV in SNAF were also significantly lower than those in CAF on HDBR 29. Moreover, TSV was close to ‘neutral’ under SNAF on HDBR 29. These data indicate that simulated natural air movement might be more effective than constant air movement at preserving core temperature at a thermoneutral ambient temperature during HDBR.     

Effects of climate on the thermoregulatory responses of male buffalo (Bubalus-bubalis) calves supplemented with different levels of testosterone and TDN

The present work was undertaken to study the changes in the thermoregulatory responses due to changing climate, androgen and TDN percent in 12 buffalo male calves from 4 months of age for a period of two years. The results obtained were: (1) The amplitudes of the diurnal cycles in rectal temperature (T_re) in each month of the experiment were very similar but longer in summer months as compared to winter months, (2) The correlation between T_re and ambient temperature (T_a) was high in all months. (3) Buffalo calves without testosterone supplementation on 70% TDN showed maximum rise in T_re by 0.076 0C per degree of ambient temperature, indicating more strain, (4) Highest respiratory frequencies occurred at 10:00 h during summer months. Subgroup 2 of group 1 showed the maximum rise by 311% in respiratory frequency in summer over winter due to least acclimatization, (5) The mean daily increase by 9.94C in ambient temperature doubled the respiratory frequency of male buffalo calves from January to April, and (6) Androgen therapy and higher TDN percent level helped the male buffalo calves to adjust better and sooner than the other calves to changing climates.     

Diurnal rhythm in the counts and types of milk somatic cells,neutrophil phagocytosis and plasma cortisol levels in Karan Fries cows during different seasons and parity

Chances of mammary infections are comparatively higher in high producing cows during harsh environmental conditions and are usually characterised by changes occurring in various somatic cells secreted in the milk and their activities. The present study was conducted to record diurnal rhythmicity in milk somatic cell counts (SCC), neutrophil: macrophage (N: M) ratio, phagocytic activity (PA) of milk neutrophils and plasma cortisol concentrations during different seasons and parity in high producing Karan Fries cows. Values of milk SCC, N: M ratio and plasma cortisol levels were lowest during thermoneutral (TN), intermediate in winter and highest during the summer season. Diurnal rhythm in the milk SCC and N: M ratio was noticed in the summer while plasma cortisol exhibited diurnal rhythm in both winter and summer seasons. Milk SCC, N: M ratio and plasma cortisol increased in multiparous cows, but diurnal variation was noticed only in the N: M ratio and plasma cortisol in cows having more than four parity. Phagocytic activity of milk neutrophils was highest during TN, intermediate in winter and lowest during the summer season. Phagocytic activity was higher and similar in cows up to fourth parity but decreased in subsequent lactation cycles. Diurnal rhythm in the PA was noticed in winter and summer seasons and in cows having more than four parity where morning samples showed higher phagocytosis as compared to the evening samples. These results can be used for immunomodulatory interventions and therapeutic approaches in treating mastitis of crossbred cows reared under tropical conditions.     

Ice slurry ingestion before and during exercise inhibit the increase in core and deep-forehead temperatures in the second half of the exercise in a hot environment

Many studies have reported that pre-exercise ice slurry ingestion improves exercise performance; however, it may increase the risk of developing heat stroke. Some studies have suggested that pre-exercise ice slurry ingestion accelerates the core temperature increase that occurs during exercise. Therefore, this study aimed to investigate whether the ingestion of ice slurry before and during exercise can inhibit this acceleration. Moreover, we measured the deep-forehead temperature (T_{deep head}) to determine whether ice slurry ingestion before and during exercise can maintain this reduction in brain temperature. Eleven male participants at room temperature (24 °C, 50% relative humidity [RH]) ingested 7.5 g/kg of ice slurry or a thermoneutral sports drink within 30 min. They then exercised for approximately 60 min at 50% of the maximal oxygen uptake in a hot environment (34 °C, 50% RH) while ingesting 1.25 g/kg of ice slurry or a thermoneutral sports drink every 10 min. Rectal temperature (T_re), T_{deep head}, forehead skin temperature, mean skin temperature, heart rate, nude body mass, and urine specific gravity were measured as physiological indices. The rating of perceived exertion, thermal sensation, and thermal comfort were measured at 5-min intervals throughout the experiment. The T_re and T_{deep head} during the second half of the exercise session were significantly reduced after ingestion of the ice slurry before and during exercise (p < 0.05). In addition, the rate of increase in T_re and T_{deep head} slowed during the second half of the exercise session after the ingestion of the ice slurry before and during exercise (p < 0.05). These results indicate that the increases in T_re and T_{deep head}, reflecting brain temperature in the second half of the exercise session, were significantly inhibited by ice slurry ingestion before and during exercise.     

Lymphocyte functions in dairy cows in hot environment

This study was carried out to ascertain the effects of intense high environmental temperatures (HET) on lymphocyte functions in periparturient dairy cows. The study was undertaken from the beginning of March through the end of July 2003 in a commercial dairy unit located approximately 40 km north of Rome. Thirty-four Holstein cows were utilised in the study. Twenty-two of these cows gave birth in spring (SP cows), from 28 March to 30 April. The remaining 12 cows gave birth in summer (SU cows), between 15 June and 2 July. The two groups of cows were balanced for parity and were fed the same rations. Blood samples were taken 4, 3, 2 and 1 week before calving, and 1, 2 and 4 weeks after calving, in order to evaluate peripheral blood mononuclear cell (PBMC) function in vitro, and to determine plasma cortisol concentrations. After isolation, the PBMC were stimulated with mitogens and their response in terms of DNA synthesis and IgM secretion was measured. During spring, either the day (9–20 h) or the night (21–8 h) temperature humidity index (THI) was below the upper critical THI (72) established for dairy cows. During summer, the mean daily THI values were 79.5±2.9 during the day and 70.1±4.7 during the night. Furthermore, during summer, three heat waves (a period of at least 3 consecutive days during which there were less than 10 recovery hours) occurred. Recovery hours were intended hours with a THI below 72. The first heat wave lasted 5 days, the second 6 days, and the third 15 days. Compared to the SP cows, over the entire periparturient period the extent of DNA synthesis and IgM secretion levels were lower (P ranging from <0.01 to 0.0001) and higher (P<0.01) respectively, in the SU cows. Before calving, the SU cows also presented higher (P<0.01) concentrations of plasma cortisol compared to the SP cows. This study indicates that the effects of HET on the immune response depend on the specific immune function under consideration, and that neuroendocrinal changes due to HET may play a role in the perturbation of immune functions.     

Changes in exercise and post-exercise core temperature under different clothing conditions

 This study evaluates the effect of different levels of insulation on esophageal (T _es) and rectal (T _re) temperature responses during and following moderate exercise. Seven subjects completed three 18-min bouts of treadmill exercise (75% VO_2max, 22°C ambient temperature) followed by 30 min of recovery wearing either: (1) jogging shoes, T-shirt and shorts (athletic clothing); (2) single-knit commercial coveralls worn over the athletic clothing (coveralls); or (3) a Canadian Armed Forces nuclear, bacteriological and chemical warfare protective overgarment with hood, worn over the athletic clothing (NBCW overgarment). T _es was similar at the start of exercise for each condition and baseline T _re was ∼0.4°C higher than T _es. The hourly equivalent rate of increase in T _es during the final 5 min of exercise was 1.8°C, 3.0°C and 4.2°C for athletic clothing, coveralls and NBCW overgarment respectively (P<0.05). End-exercise T _es was significantly different between conditions [37.7°C (SEM 0.1°C), 38.2°C (SEM 0.2°C and 38.5°C (SEM 0.2°C) for athletic clothing, coveralls and NBCW overgarment respectively)] (P<0.05). No comparable difference in the rate of temperature increase for T _re was demonstrated, except that end-exercise T _re for the NBCW overgarment condition was significantly greater (0.5°C) than that for the athletic clothing condition. There was a drop in T _es during the initial minutes of recovery to sustained plateaus which were significantly (P<0.05) elevated above pre-exercise resting values by 0.6°C, 0.8°C and 1.0°C, for athletic clothing, coveralls, and NBCW overgarment, respectively. Post-exercise T _re decreased very gradually from end-exercise values during the 30-min recovery. Only the NBCW overgarment condition T _re was significantly elevated (0.3°C) above the athletic clothing condition (P<0.05). In conclusion, T _es is far more sensitive in reflecting the heat stress of different levels of insulation during exercise and post-exercise than T _re. Physiological mechanisms are discussed as possible explanations for the differences in response. Received: 30 June 1998 / Accepted: 19 February 1999     

Effect of ambient temperature and E. coli endotoxin upon the plasma iron level in wild house mice in winter season

Summary The effects of ambient temperatures of 10°C and 30°C and of E. coli endotoxin on brain temperature and plasma iron level were investigated in unrestrained wild house mice, Mus musculus. In control animals (i.p. saline-injected) exposed to cold environmenta the brain temperature decreased and plasma iron levels were lower than those observed under thermoneutral conditions (30°C). Animals injected i.p. with endotoxin (0.5 g·kg^-1) and placed at 30°C showed a drop in plasma iron level during the fever episode. The results provide strong evidence for a relationship between brain temperature and plasma iron level in control mice under thermoneutral conditions, and show that during cold exposure or after injection of endotoxin, there is no linear correlation between brain temperature and plasma iron. Moreover, it was found that cold stress influences plasma iron level and that this influence is not mediated by changes in brain temperature.Abbreviations EP endotoxin pyrogen - T _A ambient temperature - T _Br brain temperature - T _Br change in T _Br in relation to its initial value in feverish or control mice - T _Br difference between T _Br in feverish and control mice     

Spontaneously reduced body temperature and gasping ability as a mechanism of extreme tolerance to asphyxia in neonatal rats

The aim of the investigation was to verify our hypothesis that extreme tolerance of newborn rodents to anoxia is determined by their ability to maintain reduced body temperature and to keep on gasping.Newborn Wistar rats were used. In separate experiments we checked (1) effect of extreme thermal conditions on rectal temperature (T_re) of the newborns in their nests; (2) effect of ambient temperature (T_a) on oxygen consumption; (3) effects of controlled changes in T_re on thermoregulatory and respiratory responses to anoxia and on anoxia tolerance.In their nests rat pups controlled T_re at 32–36 °C while the T_re–T_a difference changed within a range of 1–20 °C. The lowest oxygen consumption of ∼24 ml O₂ kg⁻¹ min⁻¹ was recorded at T_a of 32 °C. Pups, exposed to anoxia at their normal T_re of 33 °C, were able to decrease T_re by another 1.7 °C and they kept on extremely slow and quiescent gasping for scheduled 25 min. In contrast, rats at T_re of 37 °C and 39 °C reached a critical phase of accelerated and shallow gasping after 14.95±0.40 min and 9.25±0.30 min, respectively.In conclusion, reduced T_re and unique gasping ability make newborn rats extremely tolerant to asphyxia.     

The effects of warming by active and passive means on the subsequent responses to cold water immersion

Two experiments were undertaken to investigate the effects of warming the body upon the responses during a subsequent cold water immersion (CWI). In both experiments the subjects, wearing swimming costumes, undertook two 45-min CWIs in water at 15° C. In experiment 1, 12 subjects exercised on a cycle ergometer until their rectal temperatures (T _re) rose by an average of 0.73°C. They were then immediately immersed in the cold water. Before their other CWI they rested seated on a cycle ergometer (control condition). In experiment 2, 16 different subjects were immersed in a hot bath (40° C) until their T _re rose by an average of 0.9° C; they were then immediately immersed in the cold water. Before their other CWI they were immersed in thermoneutral water (35° C; control condition). Heart rate in both experiments and respiratory frequency in experiment 1 were significantly (P < 0.05) higher during the first 30 s of CWI following active warming. In experiment 1, the rate of fall of T _re during the final 15 min of CWI was significantly (P < 0.01) faster when CWI followed active warming (2.46° C · h^–1) compared with the control condition (1.68°C · h^–1). However, this rate was observed when absolute T _re was still above that seen in the control CWIs. It is possible, therefore, that if longer CWIs had been undertaken, the two temperature curves may have converged and thereafter fallen at similar rates; this was the case with the aural temperature (T _au) seen in experiment 1 and the T _au and T _re in experiment 2. It is concluded that pre-warming is neither beneficial nor detrimental to survival prospects during a subsequent CWI.     

Regulation of body temperature,metabolic rate,and sleep in fasting pigeons diurnally infused with glucose or saline

Summary To test the hypothesis that nocturnal body temperature (T_b) and metabolic rate (MR) in the pigeon are regulated during sleep at levels proportional to energy reserves, continuous recordings of T_b, oxygen consumption ( O₂), carbon dioxide production, and electrophysiological measures were taken from five pigeons subjected to two separate 4-day fasts. Energy reserves were depleted differentially during the fasts by 12-h diurnal infusions of either saline or isosmotic glucose solutions. Although T_b and O₂ were closely correlated, O₂ declined throughout the fast during diurnal and nocturnal phases of the 12:12 light-dark cycle whereas significant declines in T_b were restricted to the night. Diurnal thermal conductance declined over days of fasting, especially during saline infusions, and was reduced to minimal levels each night. The durations and distributions of arousal states did not change during the fast or differ between conditions. The results were consistent with the hypothesis of a nocturnal regulation of T_b and metabolic rate proportional to energy reserves.Abbreviations C ₁ thermal conductance - EEG electroencephalogram - EMG electromyogram - EOG electrooculogram - LD light-dark - MHP metabolic heat production - MR metabolic rate - REM rapid eye movement sleep - RQ respiratory quotient - SWS slow wave sleep - T _a ambient temperature - T _b body temperature - TRT total recording time - TST total sleep time - O₂ oxygen consumption     

Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type

Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake V˙O_{2 max} , body mass, body surface area (A _D),% body fat, and A _D/mass coefficient) exercised on a cycle ergometer at a relative (%V˙O_2max, REL) or an absolute (60 W) exercise intensity in a cool (CO 21°C, 50% relative humidity), warm humid (WH 35°C, 80%) and a hot dry (HD 45°C, 20%) environment. Rectal temperature (T _re) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The T _re was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with V˙O_{2 max} and V˙O_{2 max} per kilogram body mass in most climates, T _re was positively correlated with V˙O_{2 max} and V˙O_{2 max} per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined T _re and not the greater efficiency for heat loss associated with high V˙O_{2 max} . Body fatness significantly affected T _re only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, T _re was positively correlated with A _D/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable A _D/mass coefficient (high in small subjects). The total amount of variance in T _re responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%–58%) the variance explained in T _re differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%–26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions. Accepted: 4 July 1997     

Effects of rapid temperature fluctuations prior to breeding on reproductive efficiency in replacement gilts

Rapidly cooling pigs after heat stress (HS) results in a pathophysiological condition, and because rapid temperature fluctuations may be associated with reduced reproductive success in sows, it lends itself to the hypothesis that these conditions may be linked. Objectives were to determine the effects of rapid cooling on thermal response and future reproductive success in pigs. Thirty-six replacement gilts (137.8±0.9 kg BW) were estrus synchronized and then 14.1±0.4 d after estrus confirmation, pigs were exposed to thermoneutral conditions (TN; n=12; 19.7±0.9°C) for 6 h, or HS (36.3±0.5°C) for 3 h, followed by 3 h of rapid cooling (HSRC; n=12; immediate TN exposure and water dousing) or gradual cooling (HSGC; n=12; gradual decrease to TN conditions) repeated over 2 d. Vaginal (T_V) and gastrointestinal tract temperatures (T_GI) were obtained every 15 min, and blood was collected on d 1 and d 2 during the HS and recovery periods at 180 and 60 min, respectively. Pigs were bred 8.3±0.8 d after thermal treatments over 2 d. Reproductive tracts were collected and total fetus number and viability were recorded 28.0±0.8 d after insemination. HS increased T_V and T_GI (P=0.01; 0.98 °C) in HSRC and HSGC compared to TN pigs. During recovery, T_V was reduced from 15 to 105 min (P=0.01; 0.33 °C) in HSRC compared to HSGC pigs, but no overall differences in T_GI were detected (P<0.05; 39.67 °C). Rapid cooling increased (P<0.05) TNFα compared to HSGC and TN pigs during recovery-d 1 (55.2%), HS-d 2 (35.1%), and recovery-d 2 (64.9%). Viable fetuses tended to be reduced (P=0.08; 10.5%) and moribund fetuses tended to be increased (P=0.09; 159.3%) in HSRC compared to HSGC and TN pigs. In summary, rapid cooling prior to breeding may contribute to reduced fetal viability and reproductive success in pigs.     

Temperature regulation in a burrow-nesting tropical seabird,the Wedge-tailed Shearwater (Puffinus pacificus)

Summary At low air temperatures (2.3–13.9°C), Wedge-tailed Shearwaters (Puffinus pacificus) shivered and their oxygen consumption increased to as much as 283% of the mean value (0.77 ml O₂/g·h) within the thermoneutral zone of air temperature (23–34°C). The minimal thermal conductance of the tissues and plumage was similar to the value predicted from the body mass (320.5 g). The oxygen consumption of the birds within their thermoneutral zone was lower than predictions based on body mass. At elevated air temperatures, the shearwaters panted at respiratory frequencies as high as 260 respirations/min; maximal respiratory frequencies were not invoked until the birds had become hyperthermic. During exposure to a hot environment, the oxygen consumption of the birds increased and in most instances the shearwaters were not able to lose heat equivalent to their concurrent metabolic heat production.Symbols and abbreviations BMR basal metabolic rate - C _total total thermal conductance - f respiratory frequency - TEWL total evaporative water loss - T _st stomach temperature - T _re rectal temperature     

Reduced diurnal temperature range does not change warming impacts on ecosystem carbon balance of Mediterranean grassland mesocosms

Daily minimum temperature (T_min) has increased faster than daily maximum temperature (T_max) in many parts of the world, leading to decreases in diurnal temperature range (DTR). Projections suggest that these trends are likely to continue in many regions, particularly in northern latitudes and in arid regions. Despite wide speculation that asymmetric warming has different impacts on plant and ecosystem production than equal‐night‐and‐day warming, there has been little direct comparison of these scenarios. Reduced DTR has also been widely misinterpreted as a result of night‐only warming, when in fact T_min occurs near dawn, indicating higher morning as well as night temperatures. We report on the first experiment to examine ecosystem‐scale impacts of faster increases in T_min than in T_max, using precise temperature controls to create realistic diurnal temperature profiles with gradual day–night temperature transitions and elevated early morning as well as night temperatures. Studying a constructed grassland ecosystem containing species native to Oregon, USA, we found that the ecosystem lost more carbon at elevated than ambient temperatures, but remained unaffected by the 3 °C difference in DTR between symmetric warming (constantly ambient + 3.5 °C) and asymmetric warming (dawn T_min = ambient + 5 °C, afternoon T_max = ambient + 2 °C). Reducing DTR had no apparent effect on photosynthesis, probably because temperatures were most different in the morning and late afternoon when light was low. Respiration was also similar in both warming treatments, because respiration temperature sensitivity was not sufficient to respond to the limited temperature differences between asymmetric and symmetric warming. We concluded that changes in daily mean temperatures, rather than changes in T_min/T_max, were sufficient for predicting ecosystem carbon fluxes in this reconstructed Mediterranean grassland system.     

Wirkungen höher Umgebungstemperaturen auf den Wasser—und Elektrolythaushalt des Schweines in verschiedenen Wachstumsstadien

Zusammenfassung Schweine in vier verschiedenen Alters- bzw. Gewichtsstadien (20–25 kg, 40–45 kg, 60–65 kg und 90–95 kg) wurden vergleichsweise 16° bis 23°C und in der Klimakammer bei 35°C und 70–90 RF ausgesetzt. Bei erhöhter T_a stieg die Rektaltemperatur (T_re) und gleichzeitig trat in allen 4 Gruppen eine Erhöhung der Atemfrequenz, eine geringgradige Zunahme der Plasmaosmolarität, sowie eine Hyperkalämie und Hyponatriämie ein. Stieg die T_re über 40.5°C setzt eine starke Speichelsekretion ein. Die Harnosmolarität nahm bis zu einer Rektaltemperatur von 40.5°C zu, um dann wieder abzusinken. Die Na⁺-Konzentration im Harn sank mit der Erhöhung der T_re ab, während die K⁺-Konzentration anstieg.

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The effect of heat (T_a = 35°C, 70–90% rh) respiratory rate, rectal temperature (T_re), plasma and urine osmolarity, and of [Na⁺] and [K⁺] in plasma and urine in four different age/weight groups of pigs were investigated. At thermal neutral temperatures the measured physiological functions remained constant over 3 hours. At 35°C and 70–90% rh rectal temperature rose gradually. At the same time, there was a rise in respiratory rate, a slight increase in plasma osmolarity and a rise in plasma [K⁺] but a fall in plasma [Na⁺] in all four groups. The animals salivated profusely as soon as a rectal temperature of 40.5°C was reached. The urine osmolarity rose from normal to a maximum at a rectal temperature of 40.5°C and thereafter decreased. The urine [Na⁺] fell with increasing rectal temperature whereas the urine [K⁺] increased.

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Resume Des porcs de 4 classes d'âge ou plus exactement de 4 groupes de poids (20 à 25 kg, 40 à 45 kg, 60 à 65 kg et 90 à 95 kg) ont été placés soit à des températures neutres de 16 à 23°C, soit en chambre climatisée par 35°C et 70 à 90% d'humidité relative. Par température neutre, les fonctions physiologiques restent constantes durant 3 heures au moins. Par température élevée, la température rectale (T_re) se relève et, parallèlement, on constante dans les 4 groupes une augmentation de la fréquence de respiration, une faible augmentation de la pression osmotique du plasma ainsi qu'une hausse des ions [ K⁺ ], mais une diminution des ions [Na⁺] du même plasma. Les animaux ont commencé à saliver abondament dès que T_re a atteint 40,5°C. La pression osmotique de l'urine a augmenté régulièrement de la normale jusqu'à un maximum atteint lorsque T_re est arrivé à 40,5°C. Elle a diminué ensuite même si T_re dépassait ce seuil. La concentration du sodium diminue avec la hausse de T_re alors que celui du potasse augmente. On discute enfin le rôle que jouent les paramètres mesurés dans la régulation de la température et du bilan de l'eau.

     

Effect of farm and simulated laboratory cold environmental conditions on the performance and physiological responses of lactating dairy cows supplemented with bovine somatotropin (BST)

A study was conducted to evaluate the effect of bovine somatotropin (BST) supplementation in twelve lactating dairy cows maintained in cold environmental conditions. Six cows were injected daily with 25 mg of BST; the other six were injected with a control vehicle. Cows were maintained under standard dairy management during mid-winter for 30 days. Milk production was recorded twice daily, and blood samples were taken weekly. Animals were then transferred to environmentally controlled chambers and exposed to cycling thermoneutral (15° to 20° C) and cycling cold (–5° to +5° C) temperatures for 10 days in a split-reversal design. Milk production, feed and water intake, body weights and rectal temperatures were monitored. Blood samples were taken on days 1, 3, 5, 8 and 10 of each period and analyzed for plasma triiodothyronine (T³), thyroxine (T⁴), cortisol, insulin and prolactin. Under farm conditions, BST-treated cows produced 11% more milk than control-treated cows and in environmentally controlled chambers produced 17.4% more milk. No differences due to BST in feed or water intake, body weights or rectal temperatures were found under laboratory conditions. Plasma T³ and insulin increased due to BST treatment while no effect was found on cortisol, prolactin or T⁴. The results showed that the benefits of BST supplementation in lactating dairy cows were achieved under cold environmental conditions.     

The effect of body temperature on the hunting response of the middle finger skin temperature

The relationship between body temperature and the hunting response (intermittent supply of warm blood to cold exposed extremities) was quantified for nine subjects by immersing one hand in 8°C water while their body was either warm, cool or comfortable. Core and skin temperatures were manipulated by exposing the subjects to different ambient temperatures (30, 22, or 15°C), by adjusting their clothing insulation (moderate, light, or none), and by drinking beverages at different temperatures (43, 37 and 0°C). The middle finger temperature (T _fi) response was recorded, together with ear canal (T _ear), rectal (T _re), and mean skin temperature (Tˉ _sk). The induced mean T _ear changes were −0.34 (0.08) and +0.29 (0.03)°C following consumption of the cold and hot beverage, respectively. Tˉ _sk ranged from 26.7 to 34.5°C during the tests. In the warm environment after a hot drink, the initial finger temperature (T _fi,base) was 35.3 (0.4)°C, the minimum finger temperature during immersion (T _fi,min) was 11.3 (0.5)°C, and 2.6 (0.4) hunting waves occurred in the 30-min immersion period. In the neutral condition (thermoneutral room and beverage) T _fi,base was 32.1 (1.0)°C, T _fi,min was 9.6 (0.3)°C, and 1.6 (0.2) waves occurred. In the cold environment after a cold drink, these values were 19.3 (0.9)°C, 8.7 (0.2)°C, and 0.8 (0.2) waves, respectively. A colder body induced a decrease in the magnitude and frequency of the hunting response. The total heat transferred from the hand to the water, as estimated by the area under the middle finger temperature curve, was also dependent upon the induced increase or decrease in T _ear and Tˉ _sk. We conclude that the characteristics of the hunting temperature response curve of the finger are in part determined by core temperature and Tˉ _sk. Both T _fi,min and the maximal finger temperature during immersion were higher when the core temperature was elevated; Tˉ _sk seemed to be an important determinant of the onset time of the cold-induced vasodilation response. Accepted: 29 April 1997     

Diurnal rhythms of plasma growth hormone,somatostatin, thyroid hormones,cortisol and glucose concentrations in rainbow trout,Oncorhynchus mykiss,during progressive food deprivation

Abstract

The diurnal patterns of changes in plasma cortisol, growth hormone (GH), somatostatin‐14 (SRIF), thyroid hormones (L‐thyroxine, T₄ and triiodo‐L‐thyronine, T₃) and glucose were investigated in rainbow trout, Oncorhynchus mykiss, both during single meal‐feeding and during a progressive fast of 13 weeks. All measured variables exhibited a diurnal pattern in fed rainbow trout, most of which appeared to be correlated with the time of feeding (30–60 min after the onset of light), while additional changes, associated with the scotophase were also found for cortisol. Although fasting had no affect on mean daily plasma cortisol or SRIF concentrations, there was a progressive increase in mean daily plasma GH concentrations and a progressive decrease in mean daily plasma thyroid hormone and glucose concentrations associated with fasting. However, for GH, significant changes were not evident until week 10 of the fast. In addition, fasting appeared to phase‐shift the diurnal patterns of plasma GH, cortisol and glucose concentrations; the consequence of such a shift is that conclusions as to the effects of fasting, if based on a single time of sampling, may be flawed.