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PubMed1994

The effects of stress on lipoproteins and catecholamines in rats.

In order to investigate the effects of transportation stress on metabolic activities, we measured the changes in plasma lipoprotein and catecholamine levels in those rats that had just arrived in our Animal Facility and age-matched rats which had acclimatized in the Facility for at least 21 days. The acclimatized rats were considered as control, and the values from the newly arrived rats was done within 4-6 days of their arrival in the Facility. The cholesterol levels in very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) were higher (71-84%) than the control levels. Also, the stressed animals had higher levels of norepinephrine (4.5-fold) and epinephrine (3-fold) than the control levels. However, dopamine levels was 34-fold lower than that of control. On the basis of the data, we concluded that the change in plasma levels of lipoprotein and catecholamines in response to the transportation stress is significant and may require at least three weeks after the transportation to establish a stable baseline for investigations in which the plasma levels of lipoproteins and catecholamines is a critical factor.

Animals↗
PubMed1995

Long-term modulation of inward currents in O2 chemoreceptors by chronic hypoxia and cyclic AMP in vitro.

In mammals, ventilatory acclimatization to hypoxia is associated with an enhanced chemosensitivity of the O2-sensing carotid body, resulting in an increased respiratory drive. To test whether this sensitization involves long-term modulation of ion channel function in endogenous O2 chemoreceptors, i.e., type 1 cells, we exposed cultures of dissociated rat carotid body to chronic hypoxia (6% O2) for 1-2 weeks, before monitoring the electrophysiological properties of type 1 cells using whole-cell, perforated patch recording. Chronic hypoxia augmented voltage-dependent inward Na+ and Ca2+ currents in type 1 cells, without significant changes in voltage dependence of activation or steady-state inactivation. However, after normalizing for the concomitant increase in cell size, indicated by the whole-cell capacitance, only the Na+ current density was significantly enhanced. The Na+ current was sensitive to tetrodotoxin (TTX; 0.5-1 microM) or choline substitution, whereas most of the Ca2+ current was sensitive to the L-type calcium channel blocker, nifedipine (10 microM). Several of these effects of hypoxia were mimicked qualitatively by growing normoxic cultures in the presence of agents that elevate intracellular cyclic AMP, including dibutyryl cAMP (db-cAMP; 200 microM-1 mM) and forskolin (10 microM); treatment with similar concentrations of dibutyryl cyclic GMP was ineffective. Na+ channel induction by db-cAMP was abolished by the protein synthesis inhibitor, cycloheximide (90-180 microM). In current-clamp mode, these altered chemoreceptors had typical resting potentials of approximately -55 mV, and following depolarization often fired multiple spikes that appeared to consist of both short-duration Na+ and long-duration Ca2+ components. We propose that chronic hypoxia, acting in part through cAMP-dependent pathways, increases electrical excitability and calcium mobilization in type 1 cells, and these adaptations may help enhance chemosensitivity during hypoxic acclimatization.

Action Potentials↗
PubMed1993

[Type and content of adrenoceptors in toad heart].

The type and content of adrenoceptors in heart of normothermic and cold-acclimatized toad were studied by radioligand binding assay at different testing temperatures. The Bmax and Kd values of membrane from normal toad heart binding to 3H-DHA at 37 degrees C were respectively 55.11 +/- 6.22 fmol/mg protein and 2.15 +/- 0.42 nmol/L for the whole heart, 55.80 +/- 7.03 and 2.65 +/- 0.37 for sino-atrium and 54.27 +/- 3.06 and 1.84 +/- 0.14 for ventricle. While the binding to 3H-DHE was very low and nonspecific. When membrane from cold-acclimatized toad at 5-8 degrees C for 10 days was examined for its binding to 3H-DHA or 3H-DHE at 10 degrees C, the values of Bmax and Kd were as same as those of normothermic toad examined at 37 degrees C. The present results suggest that the toad heart is lacking of alpha-adrenoceptor, and the type and content of adrenoceptors are not influenced by temperature.

Animals↗
PubMed1993

Cardiac role in exercise limitation in asthmatic subjects with special reference to disease severity.

We wanted to assess limitations in cardiorespiratory fitness of asthmatic subjects, acclimatized to 1,300 m altitude and in a clinically stable state. We therefore studied 16 young asthmatic and 8 normal young subjects during an incremental bicycle exercise test. The asthmatics were divided into two groups, according to the Aas classification: a moderate asthma group (degree 2 and 3, no pulmonary impairment during symptom-free intervals), and a severe asthma group (degree 4 and 5, with persistent airway obstruction). The results showed that cardiorespiratory fitness is limited in severe asthmatic subjects acclimatized to an altitude of 1,300 m, due to decreased cardiac output and stroke volume. At submaximal exercise, the lower stroke volume is compensated by an increased arteriovenous oxygen content difference, but this compensation no longer exists at maximal exercise, which explains the lower maximal oxygen uptake in the severe asthma group. The hypothesis that the high tidal volume in the severe asthma group could lead to a decrease in left ventricular performance is considered. In conclusion, with respect to cardiorespiratory response to exercise, asthmatics should not be considered as a homogeneous group. Furthermore, relationship between ventilatory requirement and its consequences upon cardiac stroke volume provides a strong argument for the physical rehabilitation of asthmatics. Indeed, aerobic training can decrease the ventilation level for a given workload, and thus reduce inappropriate adaptations to exercise.

Adolescent↗
PubMed1993

[Prevention and therapy of altitude sickness].

Climbing in the Alps and trekking in the Andes or in the Himalayas became more and more popular in the last years. This is the reason why more and more tourists develop symptoms of acute mountain sickness (AMS) at an altitude higher than 2500 m a.s.l. To avoid an unpleasant stay at altitude, an accurate acclimatization is necessary. This can be achieved by a slow ascent at a climbing rate of 300 to 600 m in one day. If that is not possible, climbers should spend at least nine or more nights at an altitude higher than 2500 m a.s.l. in the last 30 days before ascent. This would improve performance at high altitude and significantly decrease symptoms of AMS. If acclimatization for one or another reason may not be possible or if somebody is still susceptible to AMS, pharmacological prophylaxis and treatment can be used. Drug of first choice for AMS prophylaxis is acetazolamide, a carboanhydrase inhibitor who increases ventilation. Acetazolamide has been used in a dosage of 250 to 500 mg 12 to 24 h. before ascent. If climbers have a history of high-altitude pulmonary edema (HAPE), nifedipine, a potent vasodilator which decreases pulmonary artery pressure, is the drug of the first choice and should be taken in a dosage of 3 x 20 mg, beginning one day before climbing and continuing during climbing. Prophylactic administration of nifedipine has no effect on symptoms of AMS in subjects who are not susceptible to HAPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetazolamide↗
PubMed1996

The molluscicidal activity of two 2-benzamido-5-nitrothiazole bihalogenated derivatives and niclosamide. Influence of some environmental factors on their toxicity.

Two synthetic molluscicides, 3,4-dichloro-2-benzamido-5-nitrothiazole (3,4-dichloro-BNT) and 3,5-dichloro-BNT, were studied to determine their efficacy against the snail Lymnaea glabra. Results were compared with those of a reference molluscicide, niclosamide. Snail exposure to these chemicals markedly increased overall snail mortality during the experiment (96 h). The LC50 values slightly decreased and, at day 4, were lower for the two BNT derivatives than for niclosamide. The effect of several factors on compound toxicity was also studied using lethal concentrations near LC50. Acclimatization duration under controlled conditions had a variable influence upon overall snail mortality according to the compound. No significant variation in the overall mortality was detected in snail groups exposed to 3,4-dichloro-BNT. On the other hand, snail mortality greatly increased in the 3,5-dichloro-BNT-exposed groups when the duration increased from 24 h to 15 days; the same result was obtained in the niclosamide-exposed snails acclimatized for 8 days. Snail mortality increased in the presence of sand, whatever compound was used, and greatly decreased in the presence of marl; it was also higher with water of low calcium content. When the food supply was low, snail mortality greatly decreased in the niclosamide- and 3,4-dichloro-BNT-exposed groups, whereas it increased in the case of 3,5-dichloro-BNT. In the presence of running water, the number of dead snails with 3,4-dichloro-BNT was identical to that of controls, whereas it was greater with the other molluscicides. These experiments, carried out under controlled conditions, demonstrate that the use of a molluscicide in the field must take into account its chemical properties as well as the characteristics of the snail habitat to optimally eliminate snails.

Adaptation, Physiological↗
PubMed1977

Histological features of respiratory epithelium of calves held at differing temperature and humidity.

The effect of ambient temperature and humidity on the structure of respiratory epithelium of calves was studied. Four calves of each of three experiments were acclimatized to a nonoperational environmental chamber for six days and then exposed to constant extremes of temperatures and relative humidity of one of 30 degrees C --35%, or 27 degrees C--92%, or 5 degrees C--92% respectively in this chamber for eight days each. Five calves (3 and 2) were similarly acclimatized then exposed to 1 degrees C--40%. Nasal swabs were taken from all animals at regular intervals. Swabs of three animals yielded Mycoplasma spp. and one swab yielded the virus of infectious bovine rhinotracheitis. Detailed histological studies of respiratory epithelium of nose, trachea, major bronchus and terminal bronchioli were conducted at four sites. Goblet cells were least in calves held in hot and dry air; calves held in dry air had the least polymorphonuclear cells and the greatest prevalence of hypochromatic cell layers and vacuolation of epithelial cells. Differences between experiments were evident most for sites of trachea and major bronchus.

Animals↗
PubMed1997

The effects of prolonged passive heat exposure and basic military training on thermoregulatory and cardiovascular responses in recruits from a tropical country.

This study investigates the effects of long-term passive heat exposure and a 16-week basic military training program on heat acclimatization. Thirty recruits were tested on the zero (T1), 2nd (T2), 6th (T3), and 16th (T4) weeks of the basic military training program. The trials involved 1 hour of marching on a treadmill at 5.5 km h-1, with a 5% gradient. The subjects wore their camouflage uniforms during the trials, with simulated combat loads. The trials were conducted in a climatic chamber programmed at 32 degrees C, 60% relative humidity, 900 Wm-2 of simulated solar radiation, and wind speed of 3 m s-1. There was no fluid replacement during the trials. Because only 9 subjects attended all the trials, the results presented are based on these subjects. No significant difference was found in mean skin temperature in all the four trials. Tympanic temperature was significantly reduced (p < 0.05) only at 20 minutes. Pairwise analysis was significant (p < 0.05) only between T1 (37.18 +/- 0.38 degrees C) and T4 (36.48 +/- 0.53 degrees C). Average body temperature was significantly different only at 10 and 60 minutes (p < 0.05). A significant pairwise difference (p < 0.05) was found only between T1 (36.61 +/- 0.33 degrees C) and T4 (36.07 +/- 0.46 degrees C) in 10 minutes. No pairwise difference was found at 60 minutes. Mean heart rate (HR) was significantly reduced during the 16 weeks at 10, 20, and 30 minutes. Mean HR at 10 minutes was reduced from 152.11 +/- 14.18 beats min-1 in T1 to 130.78 +/- 10.43 beats min-1 in T4 (p < 0.001). Mean HR at 20 and 30 minutes was reduced from 156.11 +/- 17.74 beats min-1 (T1) to 137.25 +/- 11.42 beats min-1 (T4) (p < 0.001), and from 157.14 +/- 15.77 beats min-1 (T1) to 146.11 +/- 12.64 beats min-1 (T4) (p < 0.05). There was no significant difference in sweat loss and mean sweat rate during the 16 weeks. This study concluded that long-term passive heat exposure was effective at inducing heat acclimatization in terms of tympanic temperature, average body temperature, mean skin temperature, sweat loss, and mean sweat rate, but not in terms of HR. Physical training was still necessary to induce further adaptation in HR. The limiting factor to task completion during the trials was physical fitness rather than beat fitness.

Analysis of Variance↗
PubMed1997

Ventilation and hypoxic ventilatory response of Tibetan and Aymara high altitude natives.

Newcomers acclimatizing to high altitude and adult male Tibetan high altitude natives have increased ventilation relative to sea level natives at sea level. However, Andean and Rocky Mountain high altitude natives have an intermediate level of ventilation lower than that of newcomers and Tibetan high altitude natives although generally higher than that of sea level natives at sea level. Because the reason for the relative hypoventilation of some high altitude native populations was unknown, a study was designed to describe ventilation from adolescence through old age in samples of Tibetan and Andean high altitude natives and to estimate the relative genetic and environmental influences. This paper compares resting ventilation and hypoxic ventilatory response (HVR) of 320 Tibetans 9-82 years of age and 542 Bolivian Aymara 13-94 years of age, native residents at 3,800-4,065 m. Tibetan resting ventilation was roughly 1.5 times higher and Tibetan HVR was roughly double that of Aymara. Greater duration of hypoxia (older age) was not an important source of variation in resting ventilation or HVR in either sample. That is, contrary to previous studies, neither sample acquired hypoventilation in the age ranges under study. Within populations, greater severity of hypoxia (lower percent of oxygen saturation of arterial hemoglobin) was associated with slightly higher resting ventilation among Tibetans and lower resting ventilation and HVR among Aymara women, although the associations accounted for just 2-7% of the variation. Between populations, the Tibetan sample was more hypoxic and had higher resting ventilation and HVR. Other systematic environmental contrasts did not appear to elevate Tibetan or depress Aymara ventilation. There was more intrapopulation genetic variation in these traits in the Tibetan than the Aymara sample. Thirty-five percent of the Tibetan, but none of the Aymara, resting ventilation variance was due to genetic differences among individuals. Thirty-one percent of the Tibetan HVR, but just 21% of the Aymara, HVR variance was due to genetic differences among individuals. Thus there is greater potential for evolutionary change in these traits in the Tibetans. Presently, there are two different ventilation phenotypes among high altitude natives as compared with sea level populations at sea level: lifelong sustained high resting ventilation and a moderate HVR among Tibetans in contrast with a slightly elevated resting ventilation and a low HVR among Aymara.

Acclimatization↗
PubMedDate not supplied

Neandertal cold adaptation: physiological and energetic factors.

European Neandertals employed a complex set of physiological cold defenses, homologous to those seen in contemporary humans and nonhuman primates. While Neandertal morphological patterns, such as foreshortened extremities and low relative surface-area, may have explained some of the variance in cold resistance, it is suggested the adaptive package was strongly dependent on a rich array of physiological defenses. A summary of the environmental cold conditions in which the Neandertals lived is presented, and a comparative ethnographic model from Tierra del Fuego is used. Muscle and subcutaneous fat are excellent "passive" insulators. Neandertals were quite muscular, but it is unlikely that they could maintain enough superficial body fat to offer much cold protection. A major, high-energy metabolic adaptation facilitated by modest amounts of highly thermogenic brown adipose tissue (BAT) is proposed. In addition, Neandertals would have been protected by general mammalian cold defenses based on systemic vasoconstriction and intensified by acclimatization, aerobic fitness, and localized cold--induced vasodilation. However, these defenses are energetically expensive. Based on contemporary data from circumpolar peoples, it is estimated that Neandertals required 3,360 to 4,480 kcal per day to support strenuous winter foraging and cold resistance costs. Several specific genetic cold adaptations are also proposed--heat shock protein (actually, stress shock protein), an ACP*1 locus somatic growth factor, and a specialized calcium metabolism not as yet understood.

Acclimatization↗
PubMedDate not supplied

Oxygen saturation and heart rate in healthy school children and adolescents living at high altitude.

This study was conducted to establish reference values for percent oxygen saturation of hemoglobin (SaO2, %) and heart rate (HR, bpm) in children living at high altitude (4,100 m) and to relate possible differences in the variables with ethnic origin. Healthy children from a mine-located school (Tintaya, n = 417), a nearby school (Marquiri, n = 474), and a rural Andean community (Nuñoa, n = 373) were investigated. The samples included different ethnic combinations, with the Nuñoa children having a predominant Quechua ancestry. Mean SaO2 for all ages was substantially lower in all high altitude children compared to values considered normal for sea level. Among the three samples, SaO2 was higher (91.3 +/- 2.7) and HR was lower (84.8 +/- 13.6) in Nuñoa than in Tintaya (SaO2, 89.8 +/- 2.5; HR, 91.7 +/- 14.9) and Marquiri (SaO2, 89.6 +/- 3.1; HR, 88.5 +/- 12.9) (P < 0.05). There was no sex difference and only a weak age-dependent trend for SaO2. Values considered abnormal at sea level were observed in all healthy high-altitude children. Higher SaO2 and lower HR in Nuñoa children may suggest a better degree of acclimatization to altitude.

Acclimatization↗
PubMed1986

High concentrations of methemoglobin in five species of temperate marine teleosts.

Blood samples from five species of marine teleosts were assayed for methemoglobin (metHb) levels during winter and summer acclimatization. There was at least 7% total hemoglobin in the met-form in all species, and as high as 27% in one species, the Atlantic cod (Gadus morhua). There was significant seasonal variation in metHb levels for three of the five species, the highest values occurring during the winter months; cunners (Tautogolabrus adspersus) 15.6% in winter and 10.1% in the summer, shorthorn sculpin (Myoxocephalus scorpius) 20.0% in the winter and 8.19% in the summer, longhorn sculpin (Myoxocephalus octodecemspinosus) 17.3-21.6% in the winter and 8.12% in the summer. The winter flounder (Pseudopleuronectes americanus) and the Atlantic cod maintained metHb concentrations constant throughout the year: 13% and 27%, respectively. There does not appear to be any relationship between the activity of a fish and the level of metHb in its blood.

Acclimatization↗
PubMed2006

Dose-response of altitude training: how much altitude is enough?

Altitude training continues to be a key adjunctive aid for the training of competitive athletes throughout the world. Over the past decade, evidence has accumulated from many groups of investigators that the "living high--training low" approach to altitude training provides the most robust and reliable performance enhancements. The success of this strategy depends on two key features: 1) living high enough, for enough hours per day, for a long enough period of time, to initiate and sustain an erythropoietic effect of high altitude; and 2) training low enough to allow maximal quality of high intensity workouts, requiring high rates of sustained oxidative flux. Because of the relatively limited access to environments where such a strategy can be practically applied, numerous devices have been developed to "bring the mountain to the athlete," which has raised the key issue of the appropriate "dose" of altitude required to stimulate an acclimatization response and performance enhancement. These include devices using molecular sieve technology to provide a normobaric hypoxic living or sleeping environment, approaches using very high altitudes (5,500m) for shorter periods of time during the day, and "intermittent hypoxic training" involving breathing very hypoxic gas mixtures for alternating 5 minutes periods over the course of 60-90 minutes. Unfortunately, objective testing of the strategies employing short term (less than 4 hours) normobaric or hypobaric hypoxia has failed to demonstrate an advantage of these techniques. Moreover individual variability of the response to even the best of living high--training low strategies has been great, and the mechanisms behind this variability remain obscure. Future research efforts will need to focus on defining the optimal dosing strategy for these devices, and determining the underlying mechanisms of the individual variability so as to enable the individualized "prescription" of altitude exposure to optimize the performance of each athlete.

Acclimatization↗
PubMed1984

Brain gangliosides and thermal adaptation in vertebrates.

Comparative studies on brain gangliosides of about 80 species belonging to all classes of vertebrates reveal: a: distinct increases in concentration with phylogenetical progress of nervous organization, b) decreases in number of single fractions, c) changes in the polarity (degree of sialylation, N- or O-acetylation of sialic acids), d) alterations in the preponderance of one of the three possible pathways of biosynthesis. In addition to these phylogenetical trends, clear correlations between the brain ganglioside composition and the state of thermal adaptation were shown: "The lower the environmental (- body) temperature, the higher the polarity of brain gangliosides". This principle was proved for ectotherms being adapted to habitats with extreme temperatures, during seasonal acclimatization and for homeotherms during early neonatal heterothermic development or during hibernation. Surface pressure-area isotherms of monolayers from single ganglioside fractions (GD1a, GD1b) or differently composed ganglioside mixtures from brains of warm- or cold-adapted hamsters as physico-chemical parameters show significant differences in their variability concerning temperature and/or Ca2+-influences. The results are taken as evidence that variations in the composition of synaptic-bound gangliosides may induce alterations in physico-chemical properties of the neuronal membrane, thus modulating synaptic transmission during temperature adaptation.

Acclimatization↗
PubMed2001

Interval hypoxic training.

Interval hypoxic training (IHT) is a technique developed in the former Soviet Union, that consists of repeated exposures to 5-7 minutes of steady or progressive hypoxia, interrupted by equal periods of recovery. It has been proposed for training in sports, to acclimatize to high altitude, and to treat a variety of clinical conditions, spanning from coronary heart disease to Cesarean delivery. Some of these results may originate by the different effects of continuous vs. intermittent hypoxia (IH), which can be obtained by manipulating the repetition rate, the duration and the intensity of the hypoxic stimulus. The present article will attempt to examine some of the effects of IH, and, whenever possible, compare them to those of typical IHT. IH can modify oxygen transport and energy utilization, alter respiratory and blood pressure control mechanisms, induce permanent modifications in the cardiovascular system. IHT increases the hypoxic ventilatory response, increase red blood cell count and increase aerobic capacity. Some of these effects might be potentially beneficial in specific physiologic or pathologic conditions. At this stage, this technique appears interesting for its possible applications, but still largely to be explored for its mechanisms, potentials and limitations.

Acclimatization↗
PubMed1995

Elevated nocturnal blood pressure assessed by ambulatory automatic monitoring during a stay at high altitude.

The aim of this study was to explore, in healthy children, the arterial blood pressure response to a 3-week stay at high altitude (4200 m). An auscultatory automatic ambulatory pressuremeter was used to avoid undue environmental influence on the measurement. The blood pressure was monitored three times in a group of ten boys, aged 10.5 (CI 0.9 years): at sea level (control values), at an altitude of 2100 m after at least 24 h of acclimatization and after at least 24 h at 4200 m altitude. Each period of monitoring extended over 24 h with 10-min intervals between successive measurements. Arterial blood pressure was evaluated separately for the night and day periods. Nocturnal recordings revealed an increase with altitude in systolic as well as in the diastolic blood pressure. Because of the technique used to gather data, this is thought to have represented an independent effect of altitude without interference from the medical environment or diurnal activity.

Acclimatization↗
PubMed1996

Lung diffusion capacity, oxygen uptake, cardiac output and oxygen transport during exercise before and after an himalayan expedition.

Studies were made of pulmonary diffusion capacity and oxygen transport before and after an expedition to altitudes at and above 4900 m. Maximum power (Pmax) and maximal oxygen uptake (VO2max) were measured in 11 mountaineers in an incremental cycle ergometer test (25W.min-1) before and after return from basecamp (30 days at 4900 m or higher). In a second test, cardiac output (Qc) and lung diffusion capacity of carbon monoxide (DL,cg) were measured by acetylene and CO rebreathing at rest and during exercise at low, medium and submaximal intensities. After acclimatization, VO2max and Pmax decreased by 5.1% [from 61.0 (SD 6.2) to 57.9 (SD 10.2) ml.kg-1, n.s.] and 9.9% [from 5.13 (SD 0.66) to 4.62 (SD 0.42) W.kg-1, n.s.], respectively. The maximal cardiac index and DL,cg decreased significantly by 15.6% [14.1 (SD 1.41) 1.min-1.m-2 to 11.9 (SD 1.44)1.min-1.m-2, P < 0.05] and 14.3% [85.9 (SD 4.36) ml.mmHg-1. min-1 to 73.6 (SD 15.2) ml.mmHg-1.min-1, P < 0.05], respectively. The expedition to high altitude led to a decrease in maximal Qc, oxygen uptake and DL,cg. A decrease in muscle mass and capillarity may have been responsible for the decrease in maximal Qc which may have resulted in a decrease of DL,cg and an increase in alveolar-arterial oxygen difference. The decrease in DL,cg especially at lower exercise intensities after the expedition may have been due to a ventilation-perfusion mismatch and changes in blood capacitance. At higher exercise intensities diffusion limitation due to reduced pulmonary capillary contact time may also have occurred.

Acclimatization↗
PubMed1979

The effect of exposure to heat on intraocular pressure.

During exposure to heat there is an increase of the intraocular pressure in nonacclimatized persons. This increase is not found after heat acclimatization has been carried out. The increase of the intraocular pressure in the nonacclimatized persons can be attributed to the increase of the body temperature due to insufficient sweating.

Acclimatization↗