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At least 1,081 records · Page 60Linked to original sources
PubMed1983

Effect of environmental temperature changes on rat liver fatty acid desaturases.

Female rats warm-adapted at 30-32 C for 20-25 days and then shifted to 13-15 C for 12, 24, 48, 72 and 120 hr showed that delta 9 desaturase and fatty acid synthetase activity decay after 24 hr of cold exposure, while delta 6 and delta 5 desaturases were increased after this period of time. These results were confirmed by an increase of arachidonic acid of heart and liver microsomes phosphatidylcholine and a decrease of oleic acid. Neither NADH-cyt b5 reductase nor NADH-cyt c reductase activity of liver microsomes were significantly affected. Male rats warm-adapted under the same conditions and then shifted to 13-15 C for 120 hr did not show significant changes in fatty acid synthetase, delta 9 and delta 6 desaturases and enzymes of the microsomal electron transport chain. Therefore, the desaturase response to environmental temperature changes could be plausibly linked to female hormones.

Animals↗
PubMed1986

Effects of estradiol and environmental temperature changes on rat liver delta 6 microsomal desaturase activity.

The regulation of delta 6 desaturase activity by environmental temperature changes was studied in the microsomal membranes from female and ovariectomized female rat liver. Female rats adapted at 30-32 C for 20-25 days and then shifted to 13-15 C for 5 days showed an increased delta 6 desaturase system. Ovariectomized rats adapted under the same conditions did not show significant changes in this enzyme. The fatty acid compositions of microsomal phosphatidylcholine showed a decrease in arachidonic acid in female rats at 30 C compared to females at 15 C and ovariectomized rats at both temperatures. These results suggest that a modification of ovaric sex hormone levels might be responsible for the different delta 6 desaturase activity in female rats acclimated at both temperatures. In this regard, serum estradiol radioimmunoassay yielded slight differences between the two groups of female rats, suggesting that estradiol could play a role in the regulation of the delta 6 desaturase. The administration of a pharmacological dose of 17-beta estradiol to female and ovariectomized rats kept at 30 and 15 C decreased the delta 6 microsomal desaturase activity. These data suggest that estradiol levels are involved in the regulation of the delta 6 desaturase during cold adaptation.

Acclimatization↗
PubMed1994

Shiftwork and heat stress in an intensive care unit.

This paper reported the results of investigation on shiftwork and heat stress in an intensive care unit. The aim of this study was to analyse the physiological strain of nurses during the three shifts (Morning, Afternoon, Night) in relation to the specific microclimatic conditions and job activities. 8 professional nurses (6 female and 2 male), aged between 21 and 38 years (mean 29.8 +/- 5.6 years), having from 3 to 18 years service, were monitored throughout a complete working cycle of 4 days. They worked on a three shift system at fast rotation. Their working environment was an independent unit for intensive care and expert surgical treatment which was entirely air conditioned. The observation indexes included: twenty-five blood parameters, ten urine parameters, net cardiac cost and relation cardiac cost, etc. The results of the investigation have not evidenced serious alterations of the psycho-physical conditions of the nurses, but do pointed out some problems pertaining both to the environmental and physiological conditions.

Adult↗
PubMed2003

Metabolism and thermoregulation in the springhare (Pedetes capensis).

Springhares are large, nocturnally active, diurnally fossorial rodents that typically inhabit arid and semi-arid areas. This lifestyle means that they need to balance excessive heat loss when foraging at night against insufficient heat loss in a potentially warm, humid burrow and both of these against the need to minimize water turnover and energy requirements. In this study we investigated metabolism and thermoregulation in these animals. Basal metabolic rate averaged 8.62+/-1.37 J g(-1) h(-1) and minimum thermal conductance 0.386+/-0.062 J g(-1) h(-1) degrees C(-1). These were higher and lower than expected, respectively. This, along with a relatively low, lower critical temperature and broad thermal neutral zone indicate that springhares are physiologically well suited to the low night-time temperatures, which they typically encounter. Body temperatures were quite labile but springhares became hyperthermic at temperatures above 30 degrees C suggesting that they are poor thermoregulators at high temperatures. This is attributed to their seldom, if ever, encountering temperatures in this range. Insufficient heat loss under normal resting conditions does not appear to be a problem, as springhares inhabit deep burrows in which the temperature never exceeds the upper critical temperature. Excess heat generated during vigorous underground exercise is presumably stored and dissipated to the cool night air or the cooler soil when subsequently resting. Water turnover and energy expenditure are presumably adequately addressed by other physiological and behavioural characteristics.

Animals↗
PubMed2005

Factors influencing the radiative surface temperature of grey seal (Halichoerus grypus) pups during early and late lactation.

The aim of this study was to examine the variation in body surface temperature of grey seal (Halichoerus grypus) pups throughout lactation in response to different environmental conditions. Radiative surface temperatures (T (r), degrees C) of pups were measured on the Isle of May (56 degrees 11'N, 02 degrees 33'W), southeast Scotland from 29 October to 25 November 2003. Records were obtained from a total of 60 pups (32 female and 28 male) from three different pupping sites during early and late lactation. Pups were sheltered from high wind speeds but air temperature, humidity and solar radiation at pupping sites were similar to general meteorological conditions. The mean T (r) of all pups was 15.8 degrees C (range 7.7-29.7 degrees C) at an average air temperature of 10.2 degrees C (range 6.5-13.8 degrees C). There was no difference in the mean T (r) of pups between early and late lactation. However, the T (r) varied between different regions of the body with hind flippers on average 2-6 degrees C warmer than all other areas measured. There was no difference in mean T (r) of male and female pups and pup body mass did not account for the variation in T (r) during early or late lactation. Throughout the day there was an increase in the T (r) of pups and this explained 20-28% of the variation in T (r) depending on stage of lactation. There was no difference in the mean T (r) of pups between pupping sites or associated with different substrate types. Wind speed and substrate temperature had no effect on the T (r) of pups. However, solar radiation, air temperature and relative humidity accounted for 48% of the variation in mean T (r) of pups during early lactation. During late lactation air temperature and solar radiation alone accounted for 43% of the variation in T (r). These results indicate that environmental conditions explain only some of the variation in T (r) of grey seal pups in natural conditions. Differences in T (r) however indicate that the cost of thermoregulation for pups will vary throughout lactation. Further studies examining intrinsic factors such as blubber thickness and activity levels are necessary before developing reliable biophysical models for grey seals.

Animals↗
PubMed2001

Intraspecific differences in behaviour and physiology: effects of captive breeding on patterns of torpor in feathertail gliders.

Studies on the physiology of mammals and birds are often conducted using captive-bred individuals and it is commonly assumed that the resulting data are representative of individuals living in the field. To investigate whether these assumptions are justified, we quantified morphological, behavioural, and physiological variables of the small marsupial feathertail glider (Acrobates pygmaeus). We compared three populations: (i) individuals from a cool-temperate, montane area, (ii) individuals form a subtropical, coastal area, and (iii) captive-bred individuals. Captive-bred gliders differed from the montane field gliders in morphology (longer tails and snouts), behaviour (longer activity periods) and physiology (less frequent torpor, shorter torpor, shallower torpor, higher metabolic rates during rest and torpor, and slower rates of rewarming). Most of these differences were also apparent between the captive-bred and the coastal field gliders. Unlike both field populations, captive-bred gliders often became hypothermic and were unable to rewarm. In contrast to the other physiological variables, the minimum body temperatures defended during torpor and the corresponding air temperatures differed between the montane and coastal field gliders, but were similar in coastal field and captive-bred gliders. Our study shows that morphology, behaviour and physiology can be strongly affected by breeding in or acclimation to captivity. The poor expression of torpor and thermal performance of the captive-bred gliders raises the question of whether they possess the physiological capability for survival in the wild. Even though captive breeding appears to have only minor effects on some physiological variables, data from captive-bred individuals should only be extrapolated to the field with caution.

Adaptation, Physiological↗
PubMed2006

Environmental stressors differentially affect leaf ecophysiological responses in two Ipomopsis species and their hybrids.

The recombination that follows natural hybridization may produce hybrid genotypes with traits that are intermediate or extreme relative to the parental species, and these traits may influence the relative fitness of the hybrids. Here we examined leaf ecophysiological traits that may influence fitness patterns in a natural plant hybrid zone. We compared the biochemical photosynthetic capacity of Ipomopsis aggregata, I. tenuituba, and early generation hybrids, as well as their photosynthetic responses to varying light and temperature, two abiotic factors found to differ among sites along the hybrid zone. In general, ecophysiological traits expressed in these plants were consistent with their natural habitat, even when grown under common greenhouse conditions. I. tenuituba reached higher photosynthetic rates (A) at higher light levels than I. aggregata, and also had a higher optimal temperature for photosynthesis (Topt). This suite of traits may reflect adaptations to the more exposed, rocky sites where I. tenuituba is found, compared to the more vegetated, mesic I. aggregata site. Hybrids had characters that were largely intermediate or tenuituba-like, but particular individual hybrids were extreme for some traits, including light saturation level, light-saturated A, and Topt. Many of these traits are consistent with adaptations reported for plants found in warm, dry sites, so they may put certain hybrids at an advantage at the relatively xeric center of the natural hybrid zone.

Carbon Dioxide↗
PubMed2006

Nocturnal respiration of lichens in their natural habitat is not affected by preceding diurnal net photosynthesis.

Dark respiration (DR) of lichens is reported to be higher in species with a high photosynthetic potential (suggesting a metabolic maintenance cost effect) and also, often in laboratory studies, transiently after photosynthesis (suggesting a substrate-driven effect). We investigated the occurrence of the latter, the effect of diurnal net photosynthesis (NP) on subsequent nocturnal DR, under natural temperate climate conditions in the chlorolichens Lecanora muralis and Cladonia convoluta and the cyanolichen Collema cristatum. Data sets totalling 15 months, 106 and 113 days, respectively, were obtained from automatic cuvettes that continually measured CO2 exchange and ambient conditions at 30 min intervals. For each 24 h period (sunrise to following sunrise), several measures of NP and DR were extracted, including maximal and mean rates and daily sums. No statistically significant correlations between the various measures of DR and preceding NP were found for L. muralis, only one weak correlation for Co. cristatum (the means of DR and NP) and three for Cl. convoluta (sums and means of DR and NP). It is proposed that even these significant correlations are actually a result of embedded codependencies between NP, DR and thallus water content. Overall it is concluded that no substrate-driven dependency of DR on preceding NP under natural conditions could be recognised. The periods of desiccation that often occur between the NP and following DR as well as the wide range of combinations of conditions would certainly contribute to this lack of relationship.

Carbon Dioxide↗
PubMed2005

Spatial variability of leaf wetness duration in different crop canopies.

The spatial variability of leaf wetness duration (LWD) was evaluated in four different height-structure crop canopies: apple, coffee, maize, and grape. LWD measurements were made using painted flat plate, printed-circuit wetness sensors deployed in different positions above and inside the crops, with inclination angles ranging from 30 to 45 degrees. For apple trees, the sensors were installed in 12 east-west positions: 4 at each of the top (3.3 m), middle (2.1 m), and bottom (1.1 m) levels. For young coffee plants (80 cm tall), four sensors were installed close to the leaves at heights of 20, 40, 60, and 80 cm. For the maize and grape crops, LWD sensors were installed in two positions, one just below the canopy top and another inside the canopy. Adjacent to each experiment, LWD was measured above nearby mowed turfgrass with the same kind of flat plate sensor, deployed at 30 cm and between 30 and 45 degrees. We found average LWD varied by canopy position for apple and maize (P<0.05). In these cases, LWD was longer at the top, particularly when dew was the source of wetness. For grapes, cultivated in a hedgerow system and for young coffee plants, average LWD did not differ between the top and inside the canopy. The comparison by geometric mean regression analysis between crop and turfgrass LWD measurements showed that sensors at 30 cm over turfgrass provided quite accurate estimates of LWD at the top of the crops, despite large differences in crop height and structure, but poorer estimates for wetness within leaf canopies.

Coffea↗
PubMed2005

Microclinal variation for ovariole number and body size in Drosophila melanogaster in 'Evolution Canyon'.

Sites that display strong environmental contrasts in close proximity, such as 'Evolution Canyon' on Mt. Carmel, Israel, are natural theatres for investigating adaptive evolution in action. We reared Drosophila melanogaster from collection sites along altitudinal transects on the north- and south-facing canyon slopes in each of three temperature environments, and assessed genetic variation in ovariole number and body size between and within collection sites, and temperature plasticity. Both traits exhibited significant genetic variation within collection sites and phenotypic plasticity in response to temperature, but not genetic variation for plasticity. Between-site genetic variation in ovariole number was negatively correlated with altitude on both slopes of the canyon, and collections from the north- and south-facing slopes were genetically differentiated for male, but not female, body size. Genetic variation between sites within easy dispersal range is consistent with the action of strong natural selection, although neither the selective agent(s) nor the direct targets of selection are known.

Adaptation, Biological↗
PubMed1981

The effects of environmental lighting on the daily melatonin rhythm in primate cerebrospinal fluid.

The effects of alterations in environmental lighting on the daily rhythm in cerebrospinal fluid concentrations of melatonin were studied in the rhesus monkey. It was found that acute exposure to darkness during the day did not markedly increase normally low daytime CSF melatonin levels, that light suppressed the normally high CSF melatonin values at night, and that 12-h phase shifts in the diurnal lighting cycle caused 12-h phase shifts in the rhythm. The daily rhythm persisted for 6.5 days of study in constant darkness and the phase of the rhythm was not affected in constant darkness by a 12-h phase shift in the daily delivery of food and daily care of the animals. These results support the notion that the melatonin rhythm in this primate species is endogenous in nature, and that light can act to both coordinate the rhythm to the 24-h day and to acutely suppress melatonin production.

Animals↗
PubMed1983

Total calorimetric measurements in the rat: influences of the sleep-wakefulness cycle and of the environmental temperature.

Rates of production as well as dry and evaporative heat loss during the sleep-wakefulness cycle were studied in 11 male, adult albino rats with chronically implanted electrodes and thermocouple re-entrant tubes. Two groups of animals chronically acclimated to 6 or 23 degrees C were acutely studied at 15, 20, 25, 30 and 35 degrees C. Statistical analysis of the data shows that rates of heat production and dry heat loss differ with respect to acclimation and acute environmental temperatures, and show significant differences depending on the states of the sleep-wakefulness cycle. Rate of heat production was highest during wakefulness, intermediate during synchronized sleep and lowest during paradoxical sleep. Rate of dry heat loss of 15 degrees C was maximal during paradoxical sleep. Rate of evaporative heat loss apparently did not change with the states of the sleep-wakefulness cycle. Heat storage estimated from difference in rates of heat production and heat loss was positive during wakefulness, slightly negative during synchronized sleep and markedly negative during paradoxical sleep. The data presented suggest a clear although partial suppression of thermoregulatory mechanisms during paradoxical sleep in the white rat.

Acclimatization↗
PubMed1985

Radioactivity connected with coal burning.

The enhanced environmental radioactivity resulting from the operation of a 72 MWe brown coal-fired power plant in central Italy is considered. A source-related control procedure is suggested. The calculated values for the atmospheric dispersion of radioactive effluents and the results of some measurements on brown coals, ash, environmental samples and gamma-exposure levels performed at representative points are reported.

Coal↗
PubMed1985

Radiation protection aspects of the use of zircon sand. National Group for Studying Radiological Implications in the Use of Zircon Sand.

Working processes using zircon sand in a factory producing refractory material were studied from the point of view of radiation protection. Zircon sand contains high concentrations of natural radionuclides and is a typical example of an enhanced source. Using various techniques the characteristics of the original material were analysed and environmental radioactivity was measured in the different significant points of the process. Finally, a first assessment was made of effective dose equivalent values in the areas of highest risk.

Air Pollutants↗
PubMed1985

Combined stack effect in houses and eskers explaining transients in radon source.

Concentrations of radon indoors and temperatures indoors and outdoors have been recorded every hour with some interruptions for one 12-week period in a dwelling situated on top of an esker outside Stockholm. The concentration of radon in the house shows variations, which can be explained as a combined stack effect in the esker and in the building. The stack effect is not only dependent on temperature differences, but also on the pressure effect that the wind creates. In this study no local wind observations have been made as this was not the main purpose on this occasion. The temperature in the esker is assumed to be at a constant level equivalent to groundwater temperature. From these data the pressure gradient has been calculated and then compared with the radon source.

Atmospheric Pressure↗
PubMed1985

A comparison of calculated indoor radiation exposure with the results of measurements.

A model has been developed for the calculation of external and internal radiation exposure of the population in dwellings. The model consists of two adjacent rooms on top of a crawl-space. The indoor gamma ray exposure rates and the radon concentrations in indoor air, predicted for a variety of conditions, are compared with observations. Predictions and observations are in reasonable agreement: for the radon concentration the predictions may be around 40% too low.

Climate↗