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At least 19 recordsLinked to original sources
PubMed1991

Respiratory, circulatory and neuropsychological responses to acute hypoxia in acclimatized and non-acclimatized subjects.

Respiratory, circulatory and neuropsychological responses to stepwise, acute exposure at rest to simulated altitude (6,000 m) were compared in ten acclimatized recumbent mountaineers 24 days, SD 11 after descending from Himalayan altitudes of at least 4,000 m with those found in ten non-acclimatized recumbent volunteers. The results showed that hypoxic hyperpnoea and O2 consumption at high altitudes were significantly lower in the mountaineers, their alveolar gases being, however, similar to those of the control group. In the acclimatized subjects the activation of the cardiovascular system was less marked, systolic blood pressure, pulse pressure, heart rate and thus (calculated) cardiac output being always lower than in the controls; diastolic blood pressure and peripheral vascular resistance, however, were maintained throughout in contrast to the vasomotor depression induced by central hypoxia which occurred in the non-acclimatized subjects at and above 4,000 m [alveolar partial pressure of O2 less than 55-50 mmHg (7.3-6.6 kPa)]. It was concluded that in the acclimatized subjects at high altitude arterial vasodilatation and neurobehavioural impairment, which in the non-acclimatized subjects reflect hypoxia of the central nervous system, were prevented; that acclimatization to high altitude resulted in a significant improvement of respiratory efficiency and cardiac economy, and that maintaining diastolic blood pressure (arterial resistance) at and above 4,000 m may represent a useful criterion for assessing hypoxia acclimatization.

Acclimatization↗
PubMed1993

De-acclimatization process of rats acclimatized to high altitude hypoxia.

The de-acclimatization process in rats acclimatized to high altitude hypoxia was analyzed according to the changes in the activities of hepatic enzymes. The activities of tryptophan 2,3-dioxygenase and tyrosine aminotransferase in the liver of non-acclimatized rats were increased, whereas those of acclimatized rats were decreased after exposure to a simulated altitude of 8,000 m. When the acclimatized rats were kept under normoxic conditions for 8 days and over, the suppression of enzyme induction was nullified, and both enzymes were induced by exposure to the simulated 8,000 m altitude. De-acclimatization of rats acclimatized to hypoxia can be completed in 8-11 days.

Acclimatization↗
PubMed2003

Arbuscular mycorrhizal fungi influence water relations, gas exchange, abscisic acid and growth of micropropagated chile ancho pepper (Capsicum annuum) plantlets during acclimatization and post-acclimatization.

Little is known about the role of arbuscular mycorrhiza fungi (AMF) on physiological changes of micropropagated plantlets during acclimatization and post-acclimatization. Using chile ancho pepper (Capsicum annuum L. cv. San Luis), measurements were made of water relations, gas exchange, abscisic acid (ABA), plantlet growth and AMF development. Plantlets had low photosynthetic rates (A) and poor initial growth during acclimatization. Relative water content (RWC) decreased during the first days after transfer from tissue culture containers to ex vitro conditions. Consequently, transpiration rates (E) and stomatal conductance (gs) declined, confirming that in vitro formed stomata were functional and able to respond ex vitro to partial desiccation--thus avoiding excessive leaf dehydration and plant death. Colonization by AMF occurred within 3 days after inoculation. Colonized plantlets had lower leaf ABA and higher RWC than noncolonized (NonAMF) plantlets during peak plant dehydration (6 days after plant transfer)--and a higher A and gs as early as days 5 and 7. During post-acclimatization [after day 8, when RWC increased and stabilized], A increased in all plantlets; however, more dramatic changes occurred with AMF plantlets. Within 48 days, 45% of the roots sampled of inoculated plantlets were colonized and had extensive arbuscule development. At this time, AMF plantlets also had greater E, A, leaf chlorophyll, leaf elemental N, P and K, leaf dry biomass and leaf area, fruit production and differences in carbon partitioning [lower root/shoot ratio and higher leaf area ratio] compared with NonAMF plantlets. Rapid AMF colonization enhanced physiological adjustments, which helped plantlets recover rapidly during acclimatization and obtain greater growth during post-acclimatization.

Abscisic Acid↗
PubMed1991

Altitude diuresis: endocrine and renal responses to acute hypoxia of acclimatized and non-acclimatized subjects.

As a result of our recently published studies we have thought that altitude diuresis resulting from hypoxic stimulation of the arterial chemoreceptors reduces the cardiac volume overload. To test this hypothesis, cardiovascular, endocrine and renal responses to stepwise acute exposure to simulated altitude (6,000 m) were compared in ten acclimatized recumbent mountaineers a mean of 24 days, SD 11, after descending from Himalayan altitudes of at least 4,000 m, with those found in ten non-acclimatized recumbent volunteers. The results showed that natriuresis and diuresis typified the renal responses to altitude exposure of both the acclimatized as well as non-acclimatized subjects, as long as altitude was well tolerated. It was concluded that the renal effects were mediated by atrial natriuretic peptide release and slight suppression of arginine-vasopressin (AVP) secretion, that the increased urine flow at altitude offset the cardiac (volume) overload resulting from hypoxic stimulation of the arterial chemoreceptors, and that enhanced AVP secretion, as found in the non-acclimatized subjects at and above 4,000 m, coincided with subjective and objective distress, i.e. with inadequate altitude adjustment owing to insufficient chemoreflex effects and central hypoxia.

Acclimatization↗
PubMed2003

Effects of exercise training on acclimatization to hypoxia: systemic O2 transport during maximal exercise.

Acclimatization to hypoxia has minimal effect on maximal O2 uptake (Vo2 max). Prolonged hypoxia shows reductions in cardiac output (Q), maximal heart rate (HR-max), myocardial beta-adrenoceptor (beta-AR) density, and chronotropic response to isoproterenol. This study tested the hypothesis that exercise training (ET), which attenuates beta-AR downregulation, would increase HRmax and Q of acclimatization and result in higher Vo2 max. After 3 wk of ET, rats lived at an inspired Po2 of 70 Torr for 10 days (acclimatized trained rats) or remained in normoxia, while both groups continued to train in normoxia. Controls were sedentary acclimatized and nonacclimatized rats. All rats exercised maximally in normoxia and hypoxia (inspired Po2 of 70 Torr). Myocardial beta-AR density and the chronotropic response to isoproterenol were reduced, and myocardial cholinergic receptor density was increased after acclimatization; all of these receptor changes were reversed by ET. Normoxic Vo2 max (in ml.min-1.kg-1) was 95.8 +/- 1.0 in acclimatized trained (n = 6), 87.7 +/- 1.7 in nonacclimatized trained (P < 0.05, n = 6), 74.2 +/- 1.4 in acclimatized sedentary (n = 6, P < 0.05), and 72.5 +/- 1.2 in nonacclimatized sedentary (n = 8; P > 0.05 acclimatized sedentary vs. nonacclimatized sedentary). A similar distribution of Vo2 max values occurred in hypoxic exercise. Q was highest in trained acclimatized and nonacclimatized, intermediate in nonacclimatized sedentary, and lowest in acclimatized sedentary groups. ET preserved Q in acclimatized rats thanks to maintenance of HRmax as well as of maximal stroke volume. Q preservation, coupled with a higher arterial O2 content, resulted in the acclimatized trained rats having the highest convective O2 transport and Vo2 max. These results show that ET attenuates beta-AR downregulation and preserves Q and Vo2 max after acclimatization, and support the idea that beta-AR downregulation partially contributes to the limitation of Vo2 max after acclimatization in rats.

Acclimatization↗
PubMed1996

Summer acclimatization in the short-tailed field vole, Microtus agrestis.

We investigated the changes that occurred in basal and noradrenaline-induced metabolic rate, body temperature and body mass in short-tailed field voles, Microtus agrestis, during exposure to naturally increasing photoperiod and ambient temperature. These parameters were first measured in winter-acclimatized voles (n = 8) and then in the same voles which had been allowed to seasonally acclimatize to photoperiod and ambient temperature (6 months later). Noradrenaline induced metabolic rate, basal metabolic rate and non-shivering thermogenesis were significantly higher in winter-acclimatized compared to summer-acclimatized voles. There was a significant positive relationship between basal metabolic rate and noradrenaline-induced metabolic rate. Body mass was significantly higher in summer-acclimatized compared to winter-acclimatized voles. There was a significant positive relationship between body mass and noradrenaline-induced metabolic rate in both winter-acclimatized and summer-acclimatized voles; however, there was no relationship between basal metabolic rate and body mass in either seasonal group of voles. Body temperature after measurements of basal metabolic rate was not significantly different in the seasonal cohorts of voles. However, body temperature was significantly higher in winter-acclimatized compared to summer-acclimatized voles after injection of noradrenaline. Previously we have found that a long photoperiod was not a sufficient stimulus to reduce thermogenic capacity in winter-acclimatized voles during cold exposure, since basal metabolic rate increased to compensate for a reduction in regulatory non-shivering thermogenesis. Here we found that a combination of increased ambient temperature and photoperiod did significantly reduce thermogenic capacity in winter-acclimatized voles. This provided evidence that the two aspects of non-shivering thermogenesis, obligatory and regulatory, are stimulated by different exogenous cues. Summer acclimatization in the short-tailed field vole is manifest as a significant decrease in both basal and noradrenaline-induced metabolic rate, combined with a significant increase in body mass.

Acclimatization↗
PubMed1966

Influence of temperature acclimatization on sodium--glucose interactions in the goldfish intestine.

1. Transmural potentials across goldfish intestines in vitro were found to depend on the acclimatization temperature of the fish. At any incubation temperature potentials were lower in fish kept previously at a high temperature, and if the transmural potentials were recorded at incubation temperatures equal to the previous acclimatization temperatures the values remained constant from 8 to 30 degrees C. The glucose-evoked potential was also reduced by previous acclimatization of the fish to a high temperature.2. As the sodium concentration was reduced the steady transmural potential increased and later fell in proportion to the low external sodium concentration, but the glucose-evoked potential fell as soon as the sodium concentration was reduced below 140 mM. Similar changes were seen with intestines taken from fish acclimatized to a high temperature but both the steady-state potential and the transitory glucose-evoked potential were more dependent on the external sodium concentration.3. The maximum glucose-evoked potential depended on the concentration of glucose used and temperature acclimatization had no significant effect on this relation. The steady potential was lower in the presence of glucose at low incubation temperatures but higher at higher incubation temperatures, and the temperature at which glucose ceased to inhibit depended on the previous acclimatization temperature. Glucose also lowered the steady potential, whatever the previous acclimatization temperature, when the external sodium concentration was low.4. The inhibitory effect of glucose on the steady potential of an intestine taken from a 30 degrees -acclimatized fish could be abolished by lowering the external concentration of glucose from 27 to 16 mM.5. Intestines taken from fish acclimatized to 3 degrees C gave variable results.6. It is concluded that sodium moves across the luminal membrane of the goldfish mucosa attached to a carrier which can exist in one of two forms. It is changes in this postulated carrier which serve to stabilize sodium transport at different acclimatization temperatures. Changes in the concentration of this postulated carrier may also occur and function in the regulation of sodium transport, particularly at acclimatization temperatures below 15 degrees C, where the switching of the carrier does not operate.

Animals↗