Effect of adaptation to high altitude on components of blood and urine of lowlanders compared with high altitude natives

Some of the blood and urinary constituents, oral glucose tolerance and urea clearance were determined in lowlanders at sea level (200 m) and at an altitude of 4, 000 m after their stay of two years. These data were compared with those of natives of high altitude area. The concentration of proteins, cholesterol, creatinephosphokinase and aspartate aminotransferase in blood among lowlanders after 2 year acclimatization were similar to that observed among highlanders. The urinary excretion of creatine and creatinine was of similar magnitude in highlanders and in acclimatized lowlanders but that of 17-keto and 17-hydroxysteroids was higher among highlanders. High altitude acclimatization among lowlanders facilitated appearance of a sharp peak in oral glucose tolerance curves and a decreased fasting blood glucose values. It also induced a restriction in renal filtration as indicated by a depressed urea clearance among lowlanders.     

Teaching the interrelationship between stress, emotions, and cardiovascular risk using a classic paper by Walter Cannon

Classroom discussion of the classic article by Walter B. Cannon in 1914, entitled "The emergency function of the adrenal medulla in pain and the major emotions," is an excellent tool to teach graduate students the interaction between stress, emotions, and cardiovascular function. Using this article, we are able to review important early research by Dr. Cannon, including discussion of his scientific methods and results and how they hold true today. This article outlines how this classic paper is used to allow students to explore basics principles of cardiovascular control during stress. The teaching points that are presented illustrate how students can be directed to understand the interrelationship between chronic stress and cardiovascular disease.     

Control of breathing and adaptation to high altitude in the bar-headed goose

The bar-headed goose flies over the Himalayan mountains on its migratory route between South and Central Asia, reaching altitudes of up to 9,000 m. We compared control of breathing in this species with that of low-altitude waterfowl by exposing birds to step decreases in inspired O(2) under both poikilocapnic and isocapnic conditions. Bar-headed geese breathed substantially more than both greylag geese and pekin ducks during severe environmental (poikilocapnic) hypoxia (5% inspired O(2)). This was entirely due to an enhanced tidal volume response to hypoxia, which would have further improved parabronchial (effective) ventilation. Consequently, O(2) loading into the blood and arterial Po(2) were substantially improved. Because air convection requirements were similar between species at 5% inspired O(2), it was the enhanced tidal volume response (not total ventilation per se) that improved O(2) loading in bar-headed geese. Other observations suggest that bar-headed geese depress metabolism less than low-altitude birds during hypoxia and also may be capable of generating higher inspiratory airflows. There were no differences between species in ventilatory sensitivities to isocapnic hypoxia, the hypoxia-induced changes in blood CO(2) tensions or pH, or hypercapnic ventilatory sensitivities. Overall, our results suggest that evolutionary changes in the respiratory control system of bar-headed geese enhance O(2) loading into the blood and may contribute to this species' exceptional ability to fly high.     

Strain and sex differences in the cardiopulmonary adaptation of rats to high altitude

On chronic exposure to hypoxia, the commercially available Hilltop (H) strain of male Sprague-Dawley rats develops severe pulmonary hypertension, right ventricular hypertrophy (RVH), and polycythemia. These signs of chronic mountain sickness are associated with a high mortality rate. In contrast, the Madison (M) strain of Sprague-Dawley rats remains healthy with significantly less severe cardiopulmonary and hematological responses. Breeding experiments under locally controlled conditions were undertaken to determine if the differences between the two strains were genetically determined and to look for possible sex differences. Following 30 to 50 days exposure to a simulated altitude of 18,000 ft, the first generation of male H rats exhibited a higher right ventricular peak systolic pressure (RVPP), a more pronounced RVH, and a greater degree of polycythemia than the male M rats. The H rats had a mortality rate of 40% in contrast to a rate of 0% in the male M rats. The first generation of female H rats also developed a higher RVPP, a greater RVH, and more severe polycythemia than that in the female M rats. There were no differences in RVPP or RVH between the males and females of either strain. Females of both strains tolerated the hypoxic exposure with a 0% mortality rate. The data suggest that the differences between the males of H and M strains in their cardiopulmonary and hematological responses and in their susceptibilities to chronic hypoxia are genetic in nature. They further suggest that the female resistance to hypoxia is not due to milder cardiopulmonary responses. Perhaps female rats tolerate RVH better than male rats, at least of the H strain.     

Comparative assessment of the effect of adaptation to stress exposure and high altitude hypoxia on heart resistance to reperfusion injury after total ischemia]

Experiments on isolated Wistar rat hearts perfused according to Langendorff showed that adaptation to stress exposure limited the depression of contraction amplitude and contracture and possessed an antiarrhythmic effect in reperfusion. Furthermore, adaptation to stress exposure efficiently limited reperfusion damage to sarcolemma. It was shown that adaptation to hypoxia did not result in any increase in the heart resistance to reperfusion damage following total ischemia. Possible mechanisms of differences in the protective effects of adaptation to stress exposure and hypoxia are discussed.     

Genome sequence of ground tit Pseudopodoces humilis and its adaptation to high altitude

Background

The mechanism of high-altitude adaptation has been studied in certain mammals. However, in avian species like the ground tit Pseudopodoces humilis, the adaptation mechanism remains unclear. The phylogeny of the ground tit is also controversial.

Results

Using next generation sequencing technology, we generated and assembled a draft genome sequence of the ground tit. The assembly contained 1.04 Gb of sequence that covered 95.4% of the whole genome and had higher N50 values, at the level of both scaffolds and contigs, than other sequenced avian genomes. About 1.7 million SNPs were detected, 16,998 protein-coding genes were predicted and 7% of the genome was identified as repeat sequences. Comparisons between the ground tit genome and other avian genomes revealed a conserved genome structure and confirmed the phylogeny of ground tit as not belonging to the Corvidae family. Gene family expansion and positively selected gene analysis revealed genes that were related to cardiac function. Our findings contribute to our understanding of the adaptation of this species to extreme environmental living conditions.

Conclusions

Our data and analysis contribute to the study of avian evolutionary history and provide new insights into the adaptation mechanisms to extreme conditions in animals.     

Teaching glucocorticoid negative feedback and adrenocortical regulation using a classic paper by Dr. Dwight Ingle

The American Physiological Society (APS) Legacy Project and its accompanying Essays on APS Classic Papers have allowed the scientific community on-line access to the entire collection of APS publications since their inception in 1898 (http://www.the-aps.org/publications/legacy/ and http://www.the-aps.org/publications/classics/). The availability of the classic physiological studies provides a unique teaching opportunity. The classic paper of Dr. Dwight Ingle represents just such a study. Dr. Ingle demonstrated that, using only purified extracts of the pituitary (ACTH) and adrenal cortex (corticosterone) and hypophysectomized rats, he could establish several of the basic principles of the control of adrenal function and glucocorticoid negative feedback that are now standard teaching material in endocrinology. An annotated figure from Dr. Ingle's paper is provided, which, when assigned to undergraduate or graduate students, will allow discovery learning. Furthermore, the brilliance and imagination of the physiologists of the last century are highlighted, which allows an appreciation of the seminal work of our predecessors.     

Effects of adaptation to intermittent high altitude hypoxia on ischemic ventricular arrhythmias in rats

We compared the effects of adaptation to intermittent high altitude (IHA) hypoxia of various degree and duration on ischemia-induced ventricular arrhythmias in rats. The animals were exposed to either relatively moderate hypoxia of 5000 m (4 or 8 h/day, 2-3 or 5-6 weeks) or severe hypoxia of 7000 m (8 h/day, 5-6 weeks). Ventricular arrhythmias induced by coronary artery occlusion were assessed in isolated buffer-perfused hearts or open-chest animals. In the isolated hearts, both antiarrhythmic and proarrhythmic effects were demonstrated depending on the degree and duration of hypoxic exposure. Whereas the adaptation to 5000 m for 4 h/day decreased the total number of premature ventricular complexes (PVCs), extending the daily exposure to 8 h and/or increasing the altitude to 7000 m led to opposite effects. On the contrary, the open-chest rats adapted to IHA hypoxia exhibited an increased tolerance to arrhythmias that was even more pronounced at the higher altitude. The distribution of PVCs over the ischemic period was not altered by any protocol of adaptation. It may be concluded that adaptation to IHA hypoxia is associated with enhanced tolerance of the rat heart to ischemic arrhythmias unless its severity exceeds a certain upper limit. The opposite effects of moderate and severe hypoxia on the isolated hearts cannot be explained by differences in the occluded zone size, heart rate or degree of myocardial fibrosis. The proarrhythmic effect of severe hypoxia may be related to a moderate left ventricular hypertrophy (27 %), which was present in rats adapted to 7000 m but not in those adapted to 5000 m. This adverse effect can be overcome by an unknown protective mechanism(s) that is absent in the isolated hearts.     

Light and electron microscopic observations on the carotid bodies of rats following adaptation to high altitude.

The carotid bodies of rats were investigated by light and electron microscopy following adaptation to a simulated altitude of 7000 m. Some animals were studied immediately after readaptation to sea-level, other groups up to 41 days later. The animals of the first group show enlarged glomera with dilated capillaries as reported earlier.The type-I-cells are large with a light staining cytoplasm. The lobular configuration of the glomus is lost and intracapillary platelet thrombosis are frequently found. Under these thrombi there is usually a chief cell degeneration with edema and vacuolisation. There is also a noticeable decrease in so-called catecholamine bodies and the remaining ones are usually arranged along the cell borders. Electron microscopically the intercapillary tissue reveals an increase in collagen material partially replanning lost chief cells. Essentially unaltered sustentacular cells frequently enclose with their processes only collagen bundles and nerve fibres. During 41 days following the readaptation there is a narrowing of capillaries and vacuolisation, swelling and thromboses are no longer observed. The amount of collagen, however, remains the same. Dense cored vesicles again increase in number and the chief cells show a prominent interdigitation. Light microscopically the restoration to normal appears to be almost complete. Fine structural analysis, however, shows an appearently permanent distortion in the composition and cellular arrangement of the glomus.     

Using a classic paper by Gottschalk and Mylle to teach the countercurrent model of urinary concentration

Most undergraduates lack the scientific background to read and appreciate much of the primary literature in physiology. Even when the underlying concepts are elegantly simple, the inherent complexity of contemporary papers often makes the work inaccessible to them. However, with a little help, they can be guided to an understanding of the creative thought processes that underlie the research and to appreciate its significance. This is especially true of many classic papers in physiology that often rely on easily comprehensible techniques. Moreover, the American Physiological Society (APS) has invited prominent scientists to select important papers in their fields and to write essays that both put the work into historical context and explain why it is scientifically important. The APS Legacy Project makes these classic papers freely available online. One such paper by Gottschalk and Mylle presents data from a series of micropuncture studies that confirm all of the predictions of the countercurrent exchange model of concentrated urine production (2). The included handout of questions for discovery learning and teaching points suggest ways to use the paper as an instructional resource.     

藏羚羊低氧诱导因子1α基因的克隆与组织表达

为探讨低氧诱导因子1α (hypoxia inducible factor l alpha,HIF-1α)在藏羚羊(Pantholops hodgsonii)高原低氧适应机制中的作用,采用RT-PCR和RACE技术克隆藏羚羊HIF-1α基因的cDNA序列,同时采用real-time PCR和Western blot方法...     

Adaptation to altitude as a vehicle for experiential learning of physiology by university undergraduates

In this article, an experiential learning activity is described in which 19 university undergraduates made experimental observations on each other to explore physiological adaptations to high altitude. Following 2 wk of didactic sessions and baseline data collection at sea level, the group ascended to a research station at 12,500-ft elevation. Here, teams of three to four students measured the maximal rate of oxygen uptake, cognitive function, hand and foot volume changes, reticulocyte count and hematocrit, urinary pH and 24-h urine volume, athletic performance, and nocturnal blood oxygen saturation. Their data allowed the students to quantify the effect of altitude on the oxygen cascade and to demonstrate the following altitude-related changes: 1) impaired performance on selected cognitive function tests, 2) mild peripheral edema, 3) rapid reticulocytosis, 4) urinary alkalinization and diuresis, 5) impaired aerobic but not anaerobic exercise performance, 6) inverse relationship between blood oxygen saturation and resting heart rate, and 7) regular periodic nocturnal oxygen desaturation events accompanied by heart rate accelerations. The students learned and applied basic statistical techniques to analyze their data, and each team summarized its results in the format of a scientific paper. The students were uniformly enthusiastic about the use of self-directed experimentation to explore the physiology of altitude adaptation and felt that they learned more from this course format than a control group of students felt that they learned from a physiology course taught by the same instructor in the standard classroom/laboratory format.     

Ovine placenta at high altitudes: comparison of animals with different times of adaptation to hypoxic environment

Fetal growth and newborn weight from ovine gestations at high altitudes (HA) are greater in ewes that live at HA for several generations than in those native to low altitudes (LA) exposed to HA only during pregnancy. Because the placenta is a key regulator of fetal growth, the present study compared placental characteristics in term pregnancies among ewes native to HA and LA. Conception occurred at HA and ewes continued to reside at HA throughout pregnancy or conception occurred at LA and ewes were transported to HA or remained at LA (controls). Ewes native to LA were moved to HA shortly after mating (group LH) and joined with pregnant ewes native to HA (group HH). After parturition, placental cotyledons were counted and measured for total area and histological estimation of surface occupied by vasculature. The total surface of the cotyledons and surface occupied by vasculature were greater at HA, whereas the number of cotyledons was smaller at HA. These changes were more pronounced in ewes of the HH compared with the LH group. The present study showed that exposure to HA induces, in pregnant ewes, placental morphological changes that may improve maternal-fetal exchange. Moreover, because of accentuation of placental changes in ewes with long-term residence at HA, this appears to be an efficient mechanism of adaptation to hypobaric hypoxia.     

Teaching the effects of gravity and intravascular and alveolar pressures on the distribution of pulmonary blood flow using a classic paper by West et al

"Distribution of blood flow in isolated lung; relation to vascular and alveolar pressures" by J. B. West, C. T. Dollery, and A. Naimark (J Appl Physiol 19: 713-724, 1964) is a classic paper, although it has not yet been included in the Essays on the American Physiological Society Classic Papers Project (http://www.the-aps.org/publications/classics/). This is the paper that originally described the "zones of the lung." The final figure in the paper, which synthesizes the results and discussion, is now seen in most textbooks of physiology or respiratory physiology. The paper is also a model of clear, concise writing. The paper and its final figure can be used to teach or review a number of physiological concepts. These include the effects of gravity on pulmonary blood flow and pulmonary vascular resistance; recruitment and distention of pulmonary vessels; the importance of the transmural pressure on the diameter of collapsible distensible vessels; the Starling resistor; the interplay of the pulmonary artery, pulmonary vein, and alveolar pressures; and the vascular waterfall. In addition, the figure can be used to generate discovery learning and discussion of several physiological or pathophysiological effects on pulmonary vascular resistance and the distribution of pulmonary blood flow.