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At least 1,081 records · Page 60Linked to original sources
PubMed2001

Melatonin rhythms in European sea bass plasma and eye: influence of seasonal photoperiod and water temperature.

The transduction of seasonal information from the environment (i.e., photoperiod and water temperature) into melatonin rhythms was studied in sea bass. Plasma and ocular melatonin (N-acetyl-5-methoxytryptamine) was determined in autumn, winter, spring and summer (experiment 1) under natural culture conditions, and in the summer and winter solstices under both natural and "6-month out-of-phase" photoperiods (experiment 2). At each sampling, 48 sea bass were sacrificed at a rate of 6 fish every 3 hr and the level of melatonin was determined in plasma and eye cup samples by ELISA. In experiment 1, significant diel changes were observed in plasma melatonin, with nocturnal melatonin varying from 144 pg/mL (summer) to 23 pg/mL (autumn), while diurnal melatonin remained low, around 8 pg/mL throughout the year. In experiment 2, the photoperiod length was shown to control the duration of the nocturnal melatonin rise, while the water temperature determined the amplitude of the melatonin rhythm. Ocular melatonin peaked during daytime in autumn and winter, but no significant changes were detected in summer and spring. In conclusion, plasma melatonin rhythms in sea bass reflect the pineal capacity to integrate seasonal information and supply precise calendar information, which may synchronize different physiological processes such as annual reproduction and feeding rhythms.

Animals↗
PubMed1999

Purification and characterization of the heat-labile alpha-amylase secreted by the psychrophilic bacterium TAC 240B.

A total of 59 bacteria samples from Antarctic sea water were collected and screened for their ability to produce alpha-amylase. The highest activity was recorded from an isolate identified as an Alteromonas species. The purified alpha-amylase shows a molecular mass of about 50,000 Da and a pI of 5.2. The enzyme is stable from pH 7.5 to 9 and has a maximal activity at pH 7.5. Compared with other alpha-amylases from mesophiles and thermophiles, the "cold enzyme" displays a higher activity at low temperature and a lower stability at high temperature. The psychrophilic alpha-amylase requires both Cl- and Ca2+ for its amylolytic activity. Br- is also quite efficient as an allosteric effector. The comparison of the amino acid composition with those of other alpha-amylases from various organisms shows that the cold alpha-amylase has the lowest content in Arg and Pro residues. This could be involved in the principle used by the psychrophilic enzyme to adapt its molecular structure to the low temperature of the environment.

Amino Acid Sequence↗
PubMed1972

The influence of deep body temperatures and skin temperatures on respiratory frequency in the pig.

1. The influences on respiratory frequency of ambient temperature, the temperature of the skin, the temperature and humidity of the inspired air, hypothalamic temperature, the temperature of the spinal cord, rectal temperature and some temperatures in the abdomen have been studied in the pig.2. At a constant ambient temperature the effect on respiratory frequency of heating a thermode in the hypothalamus was modified by the temperature of the skin of the trunk which was varied independently by means of a temperature-controlled coat. A cold skin inhibited panting; a warm skin enhanced panting. The effect of heating a thermode over the spinal cord was similarly modified by skin temperatures.3. Simultaneous heating of thermodes in the hypothalamus and spinal cord increased respiratory frequency more than heating either alone, and in a warm environment the rectal temperature influenced the extent to which respiratory frequency increased on heating the thermodes.4. Cooling the thermodes decreased respiratory frequency in a warm environment and the cooling of one thermode enhanced the effect of cooling the other.5. At a constant trunk skin temperature the effect on respiratory frequency of heating the thermode in the hypothalamus depended on ambient temperature.6. Changing the temperature of thermodes in the abdomen did not affect respiration nor was there any evidence that the temperature and humidity of the inspired air had a direct effect on respiration.

Animals↗
PubMed1996

Determination of body heat storage: how to select the weighting of rectal and skin temperatures for clothed subjects.

Two methods of estimating body heat storage were compared under differing conditions of clothing and acclimation to heat. Sixteen male subjects underwent 6 consecutive days or two 6-day periods, separated by a 1-day rest period of heat acclimation, exercising 60 min.day-1 at 45%-55% of maximal aerobic power in a hot, dry environment (dry bulb temperature 40 degrees C; relative humidity 30%; and wind speed 0.3 m.s-1). Before and after acclimation, the subjects entered the same environment, wearing either normal light combat clothing or clothing protective against nuclear, biological, and chemical agents; they walked on a treadmill at 1.34 m.s-1, 0% slope continuously (n = 11 for normal clothing) or as repeated 15-min bouts of exercise followed by 15-min sitting rest (n = 5 for normal clothing and n = 16 for protective clothing). Average exposure times were 147 min (preacclimation) and 150 min (postacclimation) for continuous exercise and 150 min (both pre- and postacclimation) for intermittent exercise while wearing normal clothing, and 103 min (preacclimation) and 116 min (postacclimation) for intermittent exercise while wearing protective clothing. Heat storage was determined calorimetrically (from heat gains and heat losses) and thermometrically [using various weightings of rectal temperature (Tre) and mean skin temperature (Tsk)]. There were only minor (<5%) differences in estimated heat storage, whether calculations used a single specific heat (3.47 kJ.kg-1.degree C-1) or a value computed according to the subject's body composition. When wearing normal clothing, a formula with an invariant relative weighting for Tre to Tsk of 4:1 provided the best thermometric estimate of heat storage. When wearing protective clothing, the invariant relative weighting of 4:1 underestimated heat storage by 2%-12%; underestimation was attenuated by using respective relative weightings for a thermoneutral and hot environment of 2:1 and 2:1 or 4:1 and 9:1 before acclimation and 4:1 and 9:1 after acclimation. We conclude that the accuracy of thermometric estimates of heat storage can be improved by modifying the weighting factors according to environment, acclimation, and type of clothing.

Adult↗
PubMed1992

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

The effects of ambient temperatures of 10 degrees C and 30 degrees 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 environment the brain temperature decreased and plasma iron levels were lower than those observed under thermoneutral conditions (30 degrees C). Animals injected i.p. with endotoxin (0.5 micrograms.kg-1) and placed at 30 degrees 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.

Acclimatization↗
PubMed1998

Effects of pH and temperature on myocardial calcium-activation in Pterygoplichthys (catfish).

Fish are chronically exposed to a wide range of temperatures and acidic environments. Fish hearts have to therefore adapt to these changes in order to maintain contractility. Myofibrillar responsiveness to Ca2+ is exquisitely sensitive to both temperature and pH in mammalian myocardium. To evaluate myofilament calcium-activation, we chemically skinned ventricular myocardium from catfish (Pterygoplichthys). A decrease in pH from 7.5 to 6.8, irrespective of temperature change, shifted the calcium-force curve towards higher calcium concentrations without affecting maximal Ca(2+)-activated force. The contractile elements are therefore sensitive to changes in pH. In intact muscle preparations the active twitch force was decreased with increasing temperature (10-22 degrees C). However, the sensitivity of the myofilaments to Ca2+ was independent of temperature. These data suggest a possible role of the sarcoplasmic reticulum (SR) in mediating the effects of temperature. The response of intact muscle preparations to changes in temperature is therefore not likely due to temperature-dependent changes in myofilament calcium responsiveness.

Actin Cytoskeleton↗
PubMed2005

Electron-transfer ion/ion reactions of doubly protonated peptides: effect of elevated bath gas temperature.

In this study, the electron-transfer dissociation (ETD) behavior of cations derived from 27 different peptides (22 of which are tryptic peptides) has been studied in a 3D quadrupole ion trap mass spectrometer. Ion/ion reactions between peptide cations and nitrobenzene anions have been examined at both room temperature and in an elevated temperature bath gas environment to form ETD product ions. From the peptides studied, the ETD sequence coverage tends to be inversely related to peptide size. At room temperature, very high sequence coverage (approximately 100%) was observed for small peptides (< or =7 amino acids). For medium-sized peptides composed of 8-11 amino acids, the average sequence coverage was 46%. Larger peptides with 14 or more amino acids yielded an average sequence coverage of 23%. Elevated-temperature ETD provided increased sequence coverage over room-temperature experiments for the peptides of greater than 7 residues, giving an average of 67% for medium-sized peptides and 63% for larger peptides. Percent ETD, a measure of the extent of electron transfer, has also been calculated for the peptides and also shows an inverse relation with peptide size. Bath gas temperature does not have a consistent effect on percent ETD, however. For the tryptic peptides, fragmentation is localized at the ends of the peptides suggesting that the distribution of charge within the peptide may play an important role in determining fragmentation sites. A triply protonated peptide has also been studied and shows behavior similar to the doubly charged peptides. These preliminary results suggest that for a given charge state there is a maximum size for which high sequence coverage is obtained and that increasing the bath gas temperature can increase this maximum.

Amino Acid Sequence↗
PubMed2006

Calculation of vibronic couplings for phenoxyl/phenol and benzyl/toluene self-exchange reactions: implications for proton-coupled electron transfer mechanisms.

The vibronic couplings for the phenoxyl/phenol and the benzyl/toluene self-exchange reactions are calculated with a semiclassical approach, in which all electrons and the transferring hydrogen nucleus are treated quantum mechanically. In this formulation, the vibronic coupling is the Hamiltonian matrix element between the reactant and product mixed electronic-proton vibrational wavefunctions. The magnitude of the vibronic coupling and its dependence on the proton donor-acceptor distance can significantly impact the rates and kinetic isotope effects, as well as the temperature dependences, of proton-coupled electron transfer reactions. Both of these self-exchange reactions are vibronically nonadiabatic with respect to a solvent environment at room temperature, but the proton tunneling is electronically nonadiabatic for the phenoxyl/phenol reaction and electronically adiabatic for the benzyl/toluene reaction. For the phenoxyl/phenol system, the electrons are unable to rearrange fast enough to follow the proton motion on the electronically adiabatic ground state, and the excited electronic state is involved in the reaction. For the benzyl/toluene system, the electrons can respond virtually instantaneously to the proton motion, and the proton moves on the electronically adiabatic ground state. For both systems, the vibronic coupling decreases exponentially with the proton donor-acceptor distance for the range of distances studied. When the transferring hydrogen is replaced with deuterium, the magnitude of the vibronic coupling decreases and the exponential decay with distance becomes faster. Previous studies designated the phenoxyl/phenol reaction as proton-coupled electron transfer and the benzyl/toluene reaction as hydrogen atom transfer. In addition to providing insights into the fundamental physical differences between these two types of reactions, the present analysis provides a new diagnostic for differentiating between the conventionally defined hydrogen atom transfer and proton-coupled electron transfer reactions.

Electrons↗
PubMed2000

The effect of environmental temperature on growth and feed conversion of broilers to 21 days of age.

Temperature during rearing is a major factor in production efficiency for broilers. The objective of this research was to determine the effect of five temperature regimens on the growth, feed conversion, and mortality of broilers to 21 d of age. This information is needed to select the most profitable conditions for broiler production. Three trials were conducted in 10 environmental chambers; five chambers were stocked with males, and five were stocked with females. The chambers were initially set at 28, 29, 30, 31, and 32 C followed by daily reductions of 0.3 C for each beginning temperature. The dewpoint was set at 15.7 C throughout the experiments. Lighting was continuous, and feed and water were provided ad libitum. Weight gain and feed conversion were determined at 7, 14, and 21 d, and mortality was recorded as it occurred. Temperature did not affect weight gain or feed conversion for any period, but males were superior to females for these parameters for the 7- to 14-d and 14- to 21-d periods. Temperature affected mortality; most of the deaths occurred during the 0- to 7-d period and at the lowest temperature treatment. These results suggest that mortality is the best indicator of the effect of rearing temperature on performance.

Animal Feed↗
PubMed1992

HomeLog: long-term recording of infant temperature, respiratory and cardiac signals in the home environment.

There is increasing evidence that overheating is a contributing factor for some cot deaths. The authors' hypothesis is that infant thermoregulation is closely related to respiratory control. HomeLog is a system built to investigate the developing thermal, respiratory and cardiac behaviour of infants in the home environment over several weeks. HomeLog is based on a modified laptop computer. Signals recorded include body temperature (from rectal and various skin sites), ambient temperature, thoracic impedance, abdominal movement and electrocardiogram (ECG). Continuous night-time recordings have been made for up to 6 weeks from infants between 1 and 4 months of age, in their own cots, in their own homes. Various time and frequency domain analyses of the breathing and temperature data have been developed. Analysis of breath rate variability and of body temperature fluctuations has confirmed sleep/wake changes. In addition, a periodic oscillation of body temperature every 1-2 h has been found, which closely matches oscillations of breath rate variability.

Apnea↗