Opioidergic Modulation of Ventilatory Response to Sustained Hypoxia in Obese Zucker Rats

Objective: To determine whether altered central and/or peripheral opioidergic mechanisms contribute to the altered ventilatory response to sustained hypoxia in obese Zucker rats. Research Methods and Procedures: Eight lean (176 ± 8 [SEM] g) and eight obese (225 ± 12 g) Zucker rats were studied at 6 weeks of age. Pulmonary ventilation (V?_E), tidal volume (V_T), and breathing frequency (f) at rest and in response to sustained (30 minutes) hypoxic (10% O₂) challenges were measured on three separate occasions by the barometric method after the randomized, blinded administration of equal volumes of saline (control), naloxone methiodide (N_M; 5 mg/kg, peripheral opioid antagonist), or naloxone hydrochloride (N_HCl; 5 mg/kg, peripheral and central opioid antagonist). Results: Administration of N_M and N_HCl in lean animals had no effect on V?_E either at rest or during 30 minutes of sustained exposure to hypoxia. Similarly, N_M failed to alter V?_E in obese rats. In contrast, N_HCl significantly (p < 0.05) increased V?_E and V_T both at rest and during 2 to 10 minutes of hypoxic exposure in obese rats. After 20 to 30 minutes of hypoxic exposure, V_T remained elevated with N_HCl, but the earlier elevation of V?_E seemed to be attenuated due to a decrease in f at 20 minutes of exposure to hypoxia. Discussion: Thus, endogenous opioids modulate both resting V?_E and the ventilatory response to sustained hypoxia in obese, but not in lean, Zucker rats by acting specifically on opioid receptors located within the central nervous system.     

甘肃鼢鼠低氧适应后心功能的变化

甘肃鼢鼠Eospalax cansus是生活在我国黄土高原地区的地下鼠,是一种缺氧耐受的模型鼠,具有多种机制来适应其特殊的生活环境。为了比较慢性间歇性低氧后与地面常氧状态下甘肃鼢鼠的心脏功能,将18只甘肃鼢鼠随机分为对照组(常氧)和实验组(慢性间歇性低氧)检测其心脏功能。结果表明,低氧适应后实验组的心率较对照组显著提高(P0.05);平均颈动脉压力、左心室收缩压较对照组极显著升高(P0.01);左心室内压最大上升速率和左心室内压最大下降速率与对照组差异无统计学意义。表明甘肃鼢鼠存在一定低氧适应机制,在低氧刺激下其心脏代偿功能得到发挥,从而减轻缺氧对其心脏的损伤。     

AltitudeOmics: Rapid Hemoglobin Mass Alterations with Early Acclimatization to and De-Acclimatization from 5260 m in Healthy Humans

It is classically thought that increases in hemoglobin mass (Hbmass) take several weeks to develop upon ascent to high altitude and are lost gradually following descent. However, the early time course of these erythropoietic adaptations has not been thoroughly investigated and data are lacking at elevations greater than 5000 m, where the hypoxic stimulus is dramatically increased. As part of the AltitudeOmics project, we examined Hbmass in healthy men and women at sea level (SL) and 5260 m following 1, 7, and 16 days of high altitude exposure (ALT1/ALT7/ALT16). Subjects were also studied upon return to 5260 m following descent to 1525 m for either 7 or 21 days. Compared to SL, absolute Hbmass was not different at ALT1 but increased by 3.7±5.8% (mean ± SD; n = 20; p<0.01) at ALT7 and 7.6±6.6% (n = 21; p<0.001) at ALT16. Following descent to 1525 m, Hbmass was reduced compared to ALT16 (−6.0±3.7%; n = 20; p = 0.001) and not different compared to SL, with no difference in the loss in Hbmass between groups that descended for 7 (−6.3±3.0%; n = 13) versus 21 days (−5.7±5.0; n = 7). The loss in Hbmass following 7 days at 1525 m was correlated with an increase in serum ferritin (r = −0.64; n = 13; p<0.05), suggesting increased red blood cell destruction. Our novel findings demonstrate that Hbmass increases within 7 days of ascent to 5260 m but that the altitude-induced Hbmass adaptation is lost within 7 days of descent to 1525 m. The rapid time course of these adaptations contrasts with the classical dogma, suggesting the need to further examine mechanisms responsible for Hbmass adaptations in response to severe hypoxia.     

The Effects of Hypoxic Hypoxia on Olfactory Sensitivity in Humans

Biophysics - This study examined the influence of hypoxic hypoxia on olfactory sensitivity in humans. Olfactory detection thresholds for n-butanol were studied when the subjects (male volunteers...     

Morphofunctional Assessment of Tissue Hypoxia Parameters in Lacunar Stroke in Humans

Human Physiology - Tissue hypoxia, developing as a consequence of vascular pathology, is a typical pathological process that underlies numerous disorders, including cerebrovascular disease. Hypoxic...     

Acclimatization to neurological decompression sickness in rabbits

Diving acclimatization refers to a reduced susceptibility to acute decompression sickness (DCS) in individuals undergoing repeated compression-decompression cycles. We demonstrated in a previous study that the mechanism responsible for this acclimatization is similar to that of stress preconditioning. In this study, we investigated the protective effect of prior DCS preconditioning on the severity of neurological DCS in subsequent exposure to high pressure in rabbits. We exposed the rabbits (n = 10) to a pressure cycle of 6 absolute atmospheres (ATA) for 90 min, which induced signs of neurological DCS in 60% of the animals. Twenty-four hours after the pressure cycle, rabbits with DCS expressed more heat-shock protein 70 (HSP70) in the lungs, liver, and heart than rabbits without signs of disease or those in the control group (n = 6). In another group of rabbits (n = 24), 50% of animals presented signs of neurological DCS after exposure to high pressure, with a neurological score of 46.5 (SD 19.5). A course of hyperbaric oxygen therapy alleviated the signs of neurological DCS and ensured the animals' survival for 24 h. Experiencing another pressure cycle of 6 ATA for 90 min, 50% of 12 rabbits with prior DCS preconditioning developed signs of DCS, with a neurological score of 16.3 (SD 28.3), significantly lower than that before hyperbaric oxygen therapy (P = 0.002). In summary, our results show that the occurrence of DCS in rabbits after rapid decompression is associated with increased expression of a stress protein, indicating that the stress response is induced by DCS. This phenomenon was defined as "DCS preconditioning." DCS preconditioning attenuated the severity of neurological DCS caused by subsequent exposure to high pressure. These results suggest that bubble formation in tissues activates the stress response and stress preconditioning attenuates tissue injury on subsequent DCS stress, which may be the mechanism responsible for diving acclimatization.     

土壤呼吸对温度升高的适应

土壤呼吸是陆地生态系统碳循环的重要环节之一 ,其对温度升高的敏感程度在相当大的程度上决定着全球气候变化与碳循环之间的反馈关系。土壤呼吸对温度升高的适应是个比较普遍的现象 ,其表现形式主要为随着温度的持续升高和升温时间的延长 ,土壤呼吸对温度升高反应的敏感程度下降。产生这一现象的机制包括影响因子主导地位的转移和温度以外其他因子的协同变化。土壤呼吸对温度升高的适应可以视为碳循环对全球变暖的负反馈效应 ,它可能会在一定程度上缓和陆地生态系统对全球气候系统之间的耦合作用 ,并且导致土壤呼吸对全球温度升高响应的时空差异。由于目前生态系统模型多数没有考虑土壤呼吸的对温度升高的适应性 ,而采用统一的 Q1 0 值 ,其对未来土壤呼吸和未来气候变化幅度的预测可能存在偏差     

Effect of Short-Term Intermittent Normobaric Hypoxia on the Regulation of External Respiration in Humans

Baseline external respiration and gas exchange values, as well as ventilatory thresholds and sensitivity to the O₂ and CO₂ stimuli in hypoxic and hypercapnic tests, were measured 1 h before and after a session of intermittent normobaric hypoxia (INH) (six repetitions with a 5-min inhalation of a gas mixture (10% O₂) alternating with a 3-min inhalation of atmospheric air). After an INH session, the background CO₂ level in the lungs increased by 10%. In the hypercapnic test, the actuation threshold of the ventilatory response did not change, whereas ventilatory sensitivity increased. The maximal pulmonary ventilation and the corresponding critical CO₂ level in the lungs also increased at the end of the test. In the hypoxic test, the ventilatory response occurred at a decreased level of blood oxygenation after an INH session, the pulmonary ventilation level being decreased and the CO₂ content in the lungs being increased at the end of the test. The data obtained evidence the maintenance of changed gas homeostasis for 1 h after an INH session. In this process, control of respiration was effected, with the hypoxic drive being weakened and the peripheral chemoreceptor sensitivity being decreased. The hypercapnic drive also increased, which may be determined by readjustment in the central mechanisms of respiratory regulation.     

Hypoxia and Exercise Increase the Transpulmonary Passage of 99mTc-Labeled Albumin Particles in Humans

Intrapulmonary arteriovenous anastomoses (IPAVs) are large diameter connections that allow blood to bypass the lung capillaries and may provide a route for right-to-left embolus transmission. These anastomoses are recruited by exercise and catecholamines and hypoxia. Yet, whether IPAVs are recruited via direct, oxygen sensitive regulatory mechanisms or indirect effects secondary to redistribution pulmonary blood flow is unknown. Here, we hypothesized that the addition of exercise to hypoxic gas breathing, which increases cardiac output, would augment IPAVs recruitment in healthy humans. To test this hypothesis, we measured the transpulmonary passage of ^99mTc-macroaggregated albumin particles (^99mTc-MAA) in seven healthy volunteers, at rest and with exercise at 85% of volitional max, with normoxic (FIO₂ = 0.21) and hypoxic (FIO₂ = 0.10) gas breathing. We found increased ^99mTc-MAA passage in both exercise conditions and resting hypoxia. However, contrary to our hypothesis, we found the greatest ^99mTc-MAA passage with resting hypoxia. As an additional, secondary endpoint, we also noted that the transpulmonary passage of ^99mTc-MAA was well-correlated with the alveolar-arterial oxygen difference (A-aDO₂) during exercise. While increased cardiac output has been proposed as an important modulator of IPAVs recruitment, we provide evidence that the modulation of blood flow through these pathways is more complex and that increasing cardiac output does not necessarily increase IPAVs recruitment. As we discuss, our data suggest that the resistance downstream of IPAVs is an important determinant of their perfusion.     

Structural Modifications of the Brain in Acclimatization to High-Altitude

Adaptive changes in respiratory and cardiovascular responses at high altitude (HA) have been well clarified. However, the central mechanisms underlying HA acclimatization remain unclear. Using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI) with fractional anisotropy (FA) calculation, we investigated 28 Han immigrant residents (17–22 yr) born and raised at HA of 2616–4200 m in Qinghai-Tibetan Plateau for at least 17 years and who currently attended college at sea-level (SL). Their family migrated from SL to HA 2–3 generations ago and has resided at HA ever since. Control subjects were matched SL residents. HA residents (vs. SL) showed decreased grey matter volume in the bilateral anterior insula, right anterior cingulate cortex, bilateral prefrontal cortex, left precentral cortex, and right lingual cortex. HA residents (vs. SL) had significantly higher FA mainly in the bilateral anterior limb of internal capsule, bilateral superior and inferior longitudinal fasciculus, corpus callosum, bilateral superior corona radiata, bilateral anterior external capsule, right posterior cingulum, and right corticospinal tract. Higher FA values in those regions were associated with decreased or unchanged radial diffusivity coinciding with no change of longitudinal diffusivity in HA vs. SL group. Conversely, HA residents had lower FA in the left optic radiation and left superior longitudinal fasciculus. Our data demonstrates that HA acclimatization is associated with brain structural modifications, including the loss of regional cortical grey matter accompanied by changes in the white matter, which may underlie the physiological adaptation of residents at HA.     

Acclimatization of Micropropagated Plants to Ex Vitro Conditions

The special conditions during in vitro culture result in the formation of plantlets of abnormal morphology, anatomy and physiology. After ex vitro transfer, these plantlets might easily be impaired by sudden changes in environmental conditions, and so need a period of acclimatization to correct the abnormalities. This review is focused upon contemporary information on the changes in leaf structure, water relations and photosynthesis during acclimatization of plantlets to ex vitro conditions. It also describes some ways of improving plant survival and for the speeding up of acclimatization. This revised version was published online in July 2006 with corrections to the Cover Date.