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PubMed1975

Ultrastructural changes in chloroplasts resulting from fluctuations in NaCl concentration: freeze-fracture of thylakoid membranes in Dunaliella salina.

The structure of chloroplasts isolated from Dunaliella salina has been studied with respect to changing concentrations of sodium chloride in the culture medium. Freeze-fracture replicas and thin sections of intact chloroplasts do not exhibit any noticeable changes in structure at concentrations ranging between 3.5 and 25% NaCl. Chloroplasts isolated from algal cells that have been acclimatized to the higher salt concentration show a change in the thylakoid membranes. The thylakoid membranes appear compressed over a major portion of the membrane surface, with only the end of the thylakoid membranes unappressed. The number of particles per unit area on the B face is also altered by the salt concentration. The chloroplasts acclimatized to 25% NaCl have about 3 times the number of particles per unit area on a B face of end-membranes as on a comparable face of thylakoid membranes acclimatized to low (3.5% NaCl) salt concentration. These morphological changes can be reversed if the chloroplasts acclimatized to high or low salt concentrations are returned to a medium of different salt concentration prior to freeze-fracturing.

Adaptation, Biological↗
PubMed2000

Myostatin and insulin-like growth factor-I and -II expression in the muscle of rats exposed to the microgravity environment of the NeuroLab space shuttle flight.

The mechanism of the loss of skeletal muscle mass that occurs during spaceflight is not well understood. Myostatin has been proposed as a negative modulator of muscle mass, and IGF-I and IGF-II are known positive regulators of muscle differentiation and growth. We investigated whether muscle loss associated with spaceflight is accompanied by increased levels of myostatin and a reduction in IGF-I and -II levels in the muscle, and whether these changes correlate with an increase in muscle proteolysis and apoptosis. Twelve male adult rats sent on the 17-day NASA STS-90 NeuroLab space flight were divided upon return to earth into two groups, and killed either 1 day later (R1) or after 13 days of acclimatization (R13). Ground-based control rats were maintained for the same periods in either vivarium (R3 and R15, respectively), or flight-simulated cages (R5 and R17, respectively). RNA and protein were isolated from the tibialis anterior, biceps femoris, quadriceps, and gastrocnemius muscles. Myostatin, IGF-I, IGF-II and proteasome 2c mRNA concentrations were determined by reverse transcription/PCR; myostatin and ubiquitin mRNA were also measured by Northern blot analysis; myostatin protein was estimated by immunohistochemistry; the apoptotic index and the release of 3-methylhistidine were determined respectively by the TUNEL assay and by HPLC. Muscle weights were 19-24% lower in the R1 rats compared with the control R3 and R5 rats, but were not significantly different after the recovery period. The myostatin/beta-actin mRNA ratios (means+/-s.e.m. ) were higher in the muscles of the R1 rats compared with the control R5 rats: 5.0-fold in tibialis (5.35 +/- 1.85 vs 1.07 +/- 0.26), 3.0-fold in biceps (2.46+/-0.70 vs 0.81 +/- 0.04), 1.9-fold in quadriceps (7.84 +/- 1.73 vs 4.08 +/- 0.52), and 2.2-fold in gastrocnemius (0.99 +/- 0.35 vs 0.44 +/- 0.17). These values also normalized upon acclimatization. Our antibody against a myostatin peptide was validated by detection of the recombinant human myostatin protein on Western blots, which also showed that myostatin immunostaining was increased in muscle sections from R1 rats, compared with control R3 rats, and normalized upon acclimatization. In contrast, IGF-II mRNA concentrations in the muscles from R1 rats were 64-89% lower than those in R3 animals. With the exception of the gastrocnemius, IGF-II was also decreased in R5 animals maintained in flight-simulated cages, and normalized upon acclimatization. The intramuscular IGF-I mRNA levels were not significantly different between the spaceflight rats and the controls. No increase was found in the proteolysis markers 3-methyl histidine, ubiquitin mRNA, and proteasome 2C mRNA. In conclusion, the loss of skeletal muscle mass that occurs during spaceflight is associated with increased myostatin mRNA and protein levels in the skeletal muscle, and a decrease in IGF-II mRNA levels. These alterations are normalized upon restoration of normal gravity and caging conditions. These data suggest that reciprocal changes in the expression of myostatin and IGF-II may contribute to the multifactorial pathophysiology of muscle atrophy that occurs during spaceflight.

Analysis of Variance↗
PubMed2005

Biodegradation characteristics of environmental endocrine disruptor di-n-butyl phthalate.

OBJECTIVE: The biodegradation characteristics of di-n-butyl phthalate (DBP), an environmental endocrine disruptor, were studied by the method of dominant bacteria and immobilized microorganisms. METHODS: Taking DBP as the only carbon source to acclimatize the collected activated sludge, the concentration of DBP increased progressively in the process of acclimatization. Plate streaking was used to separate 1 strain of the degradation dominant bacteria after acclimatization. Better conditions to degrade DBP by the bacterium could be obtained through orthogonal experiments and the bacterium was identified. Then the acclimated activated sludge was made to immobilize the microorganism using polyvinyl alcohol as entrapment agent. The immobilized microorganism degraded DBP at different conditions. RESULTS: The appropriate conditions to degrade DBP by the dominant bacteria were: degradation time, 32 h; DBP concentration, 200 mg/L; rate of shaking incubator, 100 r/min; pH, 7 and temperature, 30 degrees C. DBP could be degraded by more than 95% under such conditions. The bacteria were identified as Pseudomonas. The proliferated immobilized microorganisms degraded DBP more effectively and more adapted to temperature and pH than the free acclimated activated sludge. CONCLUSION: One strain of DBP degradation dominant bacteria was separated from the acclimatized activated sludge. It could grow with DBP as the only carbon source and energy, and degraded DBP effectively. After having been immobilized and proliferated, the dominant bacteria could keep a higher biological activity and degrade DBP more effectively than activated sludge.

Biodegradation, Environmental↗
PubMed1990

Complement activation involvement in decompression sickness of rabbits.

A hypothesis has been proposed that claims much of the phenomena of decompression sickness (DCS) are mediated by the complement system of blood plasma. This "complement hypothesis" can be used to explain the variation in susceptibility of individuals to DCS, including the phenomena of acclimatization and de-acclimatization. In this study, certain predictions of the complement hypothesis were examined by exposing rabbits to a particular pressure profile; some were observed to have symptoms of DCS and some showed none. Those that were observed to have symptoms were also found to have native complement systems that were activated by air bubbles, and those that did not show symptoms of DCS when exposed to the same pressure profile had native complement systems that were not activated by air bubbles. Rabbits that had shown symptoms of DCS the first 2 times that they were exposed to the pressure profile could be acclimatized to the pressure profile by pharmacologically decomplementing them in vivo. After being decomplemented, they showed no symptoms of DCS when they were exposed to the same pressure profile for a third time. When the decomplemented rabbits were allowed to remain inactive for a period of time that was sufficient to allow their complement systems to return to normal, after having been decomplemented, and were then subjected to the pressure profile for the fourth time, they were each again observed to have symptoms of DCS, i.e., they became de-acclimatized when their complement systems had returned to their native sensitivity. These results provide further experimental support for the complement hypothesis.

Animals↗
PubMed1987

Effects of timing and quantity of chronic dietary ethanol consumption on azoxymethane-induced colonic carcinogenesis and azoxymethane metabolism in Fischer 344 rats.

Epidemiological studies have shown an association between consumption of alcoholic beverages and carcinoma of the large bowel, but studies in experimental models of colonic carcinogenesis have yielded conflicting results. We assessed the effects on azoxymethane-induced colonic carcinogenesis of both timing of chronic dietary ethanol consumption relative to carcinogen administration and quantity of ethanol consumption. Ten-week-old male Fischer 344 rats were given 11%, 22%, or 33% of calories as reagent ethanol or no ethanol by pair feeding with Lieber-DeCarli-type liquid diets providing comparable total carbohydrates, proteins, fats, and calories. Ten weekly s.c. injections of the bowel carcinogen azoxymethane (AOM), 7 mg/kg, were given to all rats in weeks 1-10. Three experimental groups were given their respective ethanol diet during acclimatization and AOM administration (preinduction and induction phases) and then were given the no-ethanol diet from week 11 until sacrifice in week 26 (postinduction phase). Three other groups received the no-ethanol diet during acclimatization and AOM administration and then were changed to their respective ethanol diet until sacrifice. The control AOM group received the no-ethanol diet throughout the study. Suppression of colonic tumorigenesis occurred in the groups with high levels of chronic dietary ethanol consumption during acclimatization and AOM administration: in the 33% and 22% diet groups, the prevalence of colonic tumors was 3% and 20% as compared with 50% in control (P less than 0.001 and P less than 0.02, respectively). Tumorigenesis in the left colon was more affected than in the right colon, as tumor prevalence in the left colon was decreased in both the 33% and 22% diet groups (0% in both versus 24% in control, P less than 0.005), whereas prevalence in the right colon was decreased only in the 33% diet group (3% versus 38%, P less than 0.001). By contrast, prevalence of colonic tumors in the 11% diet group was not significantly different from control. Chronic dietary ethanol consumption after AOM administration had no effect on tumor outcome, regardless of quantity of consumption. In an analogous study of [14C]AOM metabolism in rats fed the 33% diet during acclimatization and AOM administration, 14CO2 was exhaled at a slower rate than in rats fed no-ethanol diet (P = 0.05), indicating suppression of AOM metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Glutamic oxalacetic and glutamic pyruvic transaminase activities in different tissues of rats and guinea pigs exposed to varying levels of altitude stress for different periods of time.

It was observed that both glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) activities were significantly increased in different tissues of both rats and guinea pigs, during a short period of altitude exposure, as well as in acclimatized animals. Interestingly, it was found that oral administration of glucose showed no such significant change at either sea level or in a hypoxic condition. Studies on the activity of GOT and GPT in different tissues of normal guinea pigs showed a little change in liver and brain during short periods of exposure. Kidney and heart showed a significant increase in GOT activity without any change in GPT activity. Increased activities were observed in all the tissues of the acclimatized animals. Of both unexposed and acclimatized animals, there was no change in the enzyme of unexposed and acclimatized animals except in heart following injection of thyroxine (16 micrograms X kg-1), but the enzyme activities were most pronounced in scorbutic animals.

Alanine Transaminase↗
PubMed1997

The assessment proposal for long-term and short-term tolerable hygrothermal microclimatic conditions.

A group of four efficient mine rescuers 25 to 35 years old were exposed to a load of a cyclo-ergometer (stages A and B) and a hand ergometer (stage E) in a climate chamber. The total 120 min period of work was divided into four work intervals, 30 min each. There were 5-min breaks between the individual intervals. The load on the ergometer was selected in the range of 25 to 150 W, Tg=20 to 40 degrees C, rh=40 to 80% and v(a)=0.2 to 1.5 m x s(-1). The thermal resistance of the working suit was 0.65 clo at stage A, 1.07 clo at stage B and 0.81 clo at stage E. A total of 200 experiments with 50 combinations of the work and climate loads were made. The heart rate, oxygen consumption, carbon dioxide production, body temperature, skin temperature, water loss by sweating and perspiration, dry and wet bulb air temperature, air velocity and globe temperature were measured during the experiments. The expected production of sweat (SR) and the amount of accumulated heat in the body (Qmax) were calculated for each combination of the work-climate conditions by a computing program ISO 7933:1989 as well as by our own program. Good agreement was reached between the measured and predicted SR values, calculated by the ISO program (r=0.871) as well as between the values calculated by the two programs, respectively (r=0.985). The experimental results have shown good agreement between the predicted and actually measured values of temperature of the body core as an index of short-term tolerable climate load. The values of short-term tolerable time of work calculated at the level of accumulated heat in the body of 50 W x h x m(-2) resulted in an increase of body core temperature by 0.8 to 1.0 K. The values of heart rate did not mostly exceed 140 beats/min, reaching in exceptional (three) cases values above 150 beats/min. The authors recommend to limit the long-term work-heat (climatic) load during a higher metabolic rate (M >80 W x m(-2) including the basal metabolic rate) of acclimatized males and females at a sweat rate SR=270 g x h(-1) x m(-2), of non-acclimatized persons at SR=206 g x h(-1) x m(-2). The limit for low metabolic rates (M < or = 80 W x m(-2)) for non-acclimatized and acclimatized persons is proposed for long-term tolerable loads of SR=147 g x h(-1) x m(-2). The short-term tolerable load by heat storage within the organism for all categories is proposed as Qmax=50 W x h x m(-2).

Adult↗
PubMed2004

Seasonal environmental changes modulate the prolactin receptor expression in an eurythermal fish.

Eurythermal fish have evolved compensatory responses to the cyclical seasonal changes of the environment. The complex adaptive mechanisms include the transduction of the physical parameters variations into molecular signals. Studies in carp have indicated that prolactin and growth hormone expression is associated with acclimatization, suggesting that the pituitary gland is a relevant physiological node in the generation of the homeostatic rearrangement that occurs in this adaptive process. Here, we report the cloning and characterization of a full-length carp prolactin receptor cDNA, which codes for the long form of the protein resembling that found in mammalian prolactin receptors. We identified up to three receptor transcript isoforms in different tissues of the teleost and assessed cell- and temporal-specific transcription and protein expression in carp undergoing seasonal acclimatization. The distinctive pattern of expression that carp prolactin receptor (cPRLr) depicts upon seasonal acclimatization supports the hypothesis that prolactin and its receptor are clearly involved in the new homeostatic stage that the eurythermal fish needs to survive during the cyclical changes of its habitat.

Acclimatization↗
PubMed2000

Seasonal adaptation modulates the expression of the protein kinase CK2 beta subunit gene in the carp.

Carp fish seasonal acclimatization induces a cyclical transcriptional modulation of several genes. Its most dramatic expression results in a concomitant structural rearrangement of the nucleolar components that phenotypically represents profound shifts in the level of ribosomal RNA synthesis. In connection with the recent studies that implicate CK2 in the control of rRNA synthesis in vertebrates, we characterized the cDNA of carp protein kinase CK2beta subunit and assessed its transcriptional behavior in winter- and summer-acclimatized fish. We found a remarkable differential gene expression of CK2beta subunit between summer- and winter-acclimatized carp which correlates with the modulatory pattern observed in rRNA transcription.

Acclimatization↗
PubMed1994

Autonomic nervous control of heart rate at altitude (5050 m).

To investigate possible changes in autonomic regulation of heart rate as a result of acclimatization to high altitude, indexes of autonomic nervous activity were obtained non invasively by spectrum analysis of heart rate variability on five healthy male subjects [age, 31 (SEM 2) years] during a postural change from supine to seated, both at sea level and after 1 month of exposure to an altitude of 5050 m. Heart rate fluctuations at the respiratory frequency (high frequency, HF) are mediated by the parasympathetic system whereas fluctuations at about 0.1 Hz (low frequency, LF) are due to both sympathetic and parasympathetic nervous systems. Maximal heart rate, as measured during an incremental exercise test, decreased from 184 (SEM 5) beats.min-1 at sea level to 152 (SEM 2) beats.min-1 at 5050 m. At sea level, the change in posture from supine to seated induced an increase in LF amplitude accompanied by an increase or a decrease in HF amplitude, whereas after 1 month at altitude the HF amplitude decreased in all subjects, with little or no change in LF amplitude. These results indicate a changed strategy of heart rate regulation after acclimatization to high altitude. At sea level, the postural change induced an increase in sympathetic activity in all subjects with different individual vagal responses, whereas at altitude the postural change induced a net decrease in vagal tone in all subjects, with little or no change in sympathetic activity. These results corroborate the reported reduced sensitivity of the heart to adrenergic drive in chronic hypoxia, which may, at least in part, explain the decreased maximal heart rate in altitude-acclimatized human subjects.

Acclimatization↗
PubMed1988

Seasonal changes in circadian rhythms of body temperatures in humans living in a dry tropical climate.

Seven volunteers (3 females and 4 males; 3 Caucasians and 4 Africans) participated in two 24 h sessions during the cool dry (CD) and the hot dry (HD) seasons of the sahelian tropical climate. Body temperatures were taken on portable cassette recorders for 24 h. Rectal (Tre) and mean skin (Tsk) temperatures decreased in the HD compared to the CD conditions, meeting one of the criteria for adaptation to heat. No ethnic differences in thermal responses were found. Males and females differed in their body temperature rhythms and in their reactions to heat. Body temperatures were higher in females than in males. Males reacted to heat with a decrease in Tre, without change in the Tre-Tsk gradient. Females showed a decrease in both Tre and Tsk, more marked for Tsk, with an increase in the Tre-Tsk gradient. It was concluded that males showed seasonal acclimatization to heat via a decrease in metabolism confirmed by a decrease in plasma levels of thyroid stimulating hormone (TSH) in the HD condition. Females showed a mixed metabolic and thermolytic type of acclimatization, with an absence of variation in plasma TSH levels. In conclusion, the steady rise in temperature between the CD and HD conditions was sufficient to trigger an acclimatization to heat similar in Caucasian and African subjects, although exposure to the external climate differed widely.

Acclimatization↗
PubMed1984

After effects of chronic hypoxia on VO2 kinetics and on O2 deficit and debt.

Single breath O2 consumption (PB = 730, FI02 = 0.21) was measured at rest, during 10 min cycloergometric exercise at 125 W, and in the following recovery phase in seven subjects before, and 12 days after 6 weeks at 5,200 m or above. Peak blood lactate after exercise (Lâb) was measured. O2 deficits and debts and half times (t1/2) of the VO2 on- and off-kinetics were calculated. Before acclimatization, the VO2 on- and off-responses were close to a single exponential with t1/2 = 30 s. After return to sea level, the VO2 on-response curves were less steep in the initial phase, becoming closer to sigmoid. The t1/2, independent of the shape of the underlying function, was approximately 10 s longer. The VO2 off-responses during the initial 4 min of recovery were the same before and after acclimatization. Average O2 deficit was approximately 320 ml larger after acclimatization: the fast component of O2 debt was similar. Since steady state VO2 and Lâb were the same, the O2 deficit difference can be attributed to a greater utilization of O2 stores. Of these, about 1/3 is explained in terms of increased mixed venous blood O2 stores, due to increased [Hb] (16.6 vs 14.9 g X dl-1), while the remainder is ascribed essentially to increased Mb-bound O2. O2 stores utilization and replenishment is presumed to occur when muscle metabolism is low; as a consequence, while it is clearly detectable from the shape of the initial phase of the VO2 on-response, during recovery it is spread throughout, thus becoming more difficult to appreciate.

Acclimatization↗
PubMed2005

Seasonal adjustments in body mass and thermogenesis in Mongolian gerbils (Meriones unguiculatus): the roles of short photoperiod and cold.

Seasonal adjustments in body mass and thermogenesis are important for the survival of small mammals during acclimatization in the temperate zone. To determine the contributions of short photoperiod and cold temperatures to seasonal changes in thermogenesis and body mass in Mongolian gerbils (Meriones unguiculatus), body mass, basal metabolic rate (BMR), nonshivering thermogenesis (NST), energy intake and energy digestibility were determined in seasonally acclimatized and laboratory acclimated animals. Body mass showed significant seasonal changes and decreased to a minimum in winter. Both BMR and NST increased in winter, and these changes were mimicked by exposing animals to short photoperiod or cold temperatures in the animal house. Digestible energy intake also increased significantly in winter, and also during exposure of housed animals to both short photoperiod and cold. These results suggest that Mongolian gerbils overcome winter thermoregulatory challenges by increasing energy intake and thermogenesis, and decreasing body mass to reduce total energy requirements. Short photoperiod and cold can serve as effective environmental cues during seasonal acclimatization.

Acclimatization↗
PubMed1977

Hypoxic ventilatory response of cats at high altitude: an interpretation of 'blunting'.

Cats acclimatized to a simulated altitude of 5500 m developed attenuated ventilatory response in the hypoxic test range of PAO2 = 60-45 torr, but their CO2 response remained normal, although the curve was shifted to a lower PACO2 range. The acclimatized cats a high respiratory frequency and maintained hyperventilation under normoxia. Cats from 3100 m altitude had hypoxic reponses which were, on the average, slightly below sea level standards, but the difference was not statistically significant. Two cats raised at 4640 m had a normal hypoxic ventilatory response even though the frequency response was 'blunted'. These data suggest the possibility of hypoxic 'threshold' near 5500 m to produce an attenuation effect. Another series of cats acclimatized to 5500 m were tested with more severe hypoxia, and they exhibited brisk ventilatory response in range PAO2, 40-25 torr, although they showed typical 'blunting' in the range PAO2, 60-45 torr. These results suggested that the phenomenon of attenuated hypoxic response at high altitude was a reflection of shift of hypoxic set point to a lower PAO2. Finally, it was shown that the hypoxic responses of 'blunted' animals were restored to normal after mid-collicular decerebration; and that decortication resulted in a typical hyperexcitability of the hypoxic response. These results are discussed in terms of hypothesized suprapontine modulating influences on the control of breathing, and possiblities for a contribution of these mechanisms in pathogenesis of hypoxic 'blunting' are raised.

Acclimatization↗
PubMed1983

Metabolic meaning of elevated levels of oxidative enzymes in high altitude adapted animals: an interpretive hypothesis.

It is commonly observed that during acclimatization to altitude oxidative enzyme activities increase per g wet weight of tissue. To examine this problem in long-term adapted animals we measured citrate synthase (CS), hydroxyacylCoA dehydrogenase (HOAD), pyruvate kinase (PK), and lactate dehydrogenase (LDH) activities/g of myocardium in two domestic species (llama and alpaca) and a high altitude deer, the taruca. In all these species, we found an upward scaling of oxidative capacity (indicated by absolute activities of CS and HOAD) but a downward scaling of anaerobic/aerobic metabolic potentials of the heart (indicated by low ratios of LDH/CS, and LDH/HOAD, but high ratios of PK/LDH). As the direction and magnitude of these long-term adaptations are the same as in shorter-term acclimatizations, we wondered why a similar pattern at the enzyme level correlates with the right shift of the O2 dissociation curve (ODC) in the latter case, but with a left shifted ODC in the former. We hypothesize that in the long term, increased oxidative enzyme activities allow increased maximum flux capacity of aerobic metabolism. This in turn calls for physiological adjustments in O2 transfer systems; flux limits of the former must be matched by flux limits of the latter. Only then can an acceptably high scope for aerobic activity be achieved despite reduced O2 availability in inspired air. Such long-term match-up invariably calls for a left-shifted ODC plus other well known adjustments in O2 transport. In the short term, right shifting the ODC may increase the total amount of aerobic work possible (by favoring O2 unloading and thus raising tissue O2 concentration), yet maximum flux capacity cannot be changed much because mitochondrial metabolism is designed for maintaining stable rates of ATP synthesis even at widely varying O2 tensions. That is why even in short-term acclimatization, in order to increase flux capacity, the activities of oxidative enzymes also must be increased.

Acclimatization↗
PubMed1993

Oxygen and avian eggshell formation at high altitude.

Many birds at high altitude lay eggs with reduced eggshell diffusive conductance to water vapor. Disagreement exists about the cause, but hypotheses include physiological acclimatization and genetic adaptation. To investigate this, we tested for the occurrence of physiological acclimatization and quantified the effect of relieving hypoxia at high altitude. Ten laying hens (Gallus domesticus) were exposed to elevations of 3800 m (PIO2 90 Torr), 3800 m with supplementary oxygen (PIO2 140 Torr), and 1200 m (PIO2 125 Torr). 573 eggs were collected and analyzed during the 17-week experiment. Shell conductance, aggregate pore area, and shell thickness were reduced at 3800 m compared to 1200 m or 3800 m with supplementary oxygen. There was a lag in the response to changes in altitude or PIO2 that corresponded to a time constant of approximately 2.5 weeks. We conclude that physiological acclimatization of eggshell conductance occurs in some chickens, and that it is probably stimulated by hypoxia.

Acclimatization↗
PubMed1996

Smaller alveolar-arterial O2 gradients in Tibetan than Han residents of Lhasa (3658 m).

Previous studies have indicated that native Tibetans have a larger lung capacity and better maintain arterial O2 saturation during exercise than Han ("Chinese") acclimatized lowlanders. To test if differences in ventilation or alveolar-arterial O2 gradient (A-aDO2) were responsible, we compared 10 lifelong Tibetan and 9 Han acclimatized newcomer residents of Lhasa (3658 m) at rest and during progressive exercise. Resting blood gas tensions and arterial O2 saturation in the two groups were similar. During exercise the Tibetans had lower total ventilation and higher arterial CO2 tensions than the Han (both P < 0.01) and markedly lower A-aDO2 (7 +/- 1 vs. 11 +/- 1, 13 +/- 1 vs. 18 +/- 1, and 14 +/- 1 vs. 20 +/- 1 mmHg at light, medium, and heavy workloads respectively, all P < 0.01). The Tibetans' narrower A-aDO2 compensated for their lower exercise ventilation such that arterial O2 tension and saturation were raised above acclimatized newcomer values and better maintained during exercise. We concluded that the Tibetans exhibited more efficient pulmonary gas exchange which compensated for reduced ventilation and lessened respiratory effort.

Acclimatization↗
PubMed2004

Performance of BTX degraders under substrate versatility conditions.

A microbial consortium acclimatized with benzene, toluene or xylene (BTX) was employed to study the degradation pattern of these compounds individually under aerobic conditions. Batch and continuous experiments were conducted to evaluate the adaptability of the enriched cultures under substrate versatility conditions. The bio-kinetic parameters obtained under substrate versatility conditions were compared with those of a single substrate condition. Similar degradation patterns were observed for all the substrates with inhibition occurring at higher concentration (approximately 150 mg/L for benzene and xylene, and approximately 200 mg/L for toluene). Toluene degradation was highest, followed by benzene and xylene in the aqueous phase. Adaptation to a more toxic compound like benzene and xylene improved the utilization of toluene. On the other hand, microbes grown on a less toxic compound (toluene) grew at a lower rate in the presence of more toxic compounds. Suitable kinetic parameters such as micro(max) (maximum specific growth rate per hour), Ks (half saturation constant, mg/L), and KI (threshold substrate inhibition constant, mg/L) were determined using Haldane and Levenspiel substrate inhibition models. The Haldane equation seems to be an adequate expression for the system. The degradation behavior of pollutants in the gas phase was also evaluated using a toluene acclimatized biotrickling filter operated in continuous mode. The biotrickling filter acclimatized with toluene could degrade benzene and xylene with a lower elimination capacity. But, the system could recover its original efficiency quite fast even after a prolonged shock loading. The degradation was better for toluene, followed by benzene and xylene.

Acclimatization↗