Morphological and physiological responses to altitude in deer mice Peromyscus maniculatus.

Individuals within a species, living across a wide range of habitats, often display a great deal of phenotypic plasticity for organ mass and function. We investigated the extent to which changes in organ mass are variable, corresponding to environmental demand, across an altitudinal gradient. Are there changes in the mass of oxygen delivery organs (heart and lungs) and other central processing organs (gut, liver, kidney) associated with an increased sustainable metabolic rate that results from decreased ambient temperatures and decreased oxygen availability along an altitudinal gradient? We measured food intake, resting metabolic rate (RMR), and organ mass in captive deer mice (Peromyscus maniculatus bairdii) at three sites from 1,200 to 3,800 m above sea level to determine whether energy demand was correlated with organ mass. We found that food intake, gut mass, and cardiopulmonary organ mass increased in mice living at high altitudes. RMR was not correlated with organ mass differences along the altitudinal gradient. While the conditions in this study were by no means extreme, these results show that mice living at high altitudes have higher levels of energy demand and possess larger cardiopulmonary and digestive organs than mice living at lower altitudes.     

Unchanged in vivo P50 at high altitude despite decreased erythrocyte age and elevated 2,3-diphosphoglycerate

We measured hematological and erythrocyte O2 transport parameters in whole blood and density-separated erythrocytes in 11 mountaineers before and during 5 days of exposure to high altitude (4,559 m). We determined the in vivo (arterial pHblood and PCO2) and standard (pHblood = 7.4, PCO2 = 40 Torr) O2 tension at 50% O2 saturation of hemoglobin and (P50,vv and P50,st) and Bohr coefficients (BC) for fixed acid (H+) and CO2 and examined the contribution of the altered average age of circulating erythrocytes due to the stimulation of erythropoiesis on whole blood 2,3-diphosphoglycerate (2,3-DPG) and P50,st. At altitude, whole blood P50,vv remained almost unchanged, whereas P50,st and 2,3-DPG increased significantly (+4 Torr; 3.5 mumol/g hemoglobin). BCCO2 was elevated significantly at altitude. Serum erythropoietin increased transiently fourfold, iron utilization increased, and serum iron decreased by 66%. Reticulocyte counts increased, but other hematological parameters were unchanged. In density-separated erythrocytes, P50,st and 2,3-DPG increased with decreasing cell density but were higher in fractions with comparable reticulocyte counts in cells prepared at altitude than in those from control studies. Our data show that, despite the increase in 2,3-DPG and the decrease in average erythrocyte age, the in vivo hemoglobin-O2 affinity remains unchanged. P50,st values reflect the elevation of 2,3-DPG, and approximately 50% of the increase in both parameters can be ascribed to the increase in the number of reticulocytes and young erythrocytes.     

Thoracic adaptation to high altitude

Growth in the thoracic region and its adaptation to higher altitude was investigated in boys between 5 to 18 years of Rajput origin at two altitudes, i. e. Rampur Bushahr (800 m above sea level) and Kinnaur (3,000 m above sea level). Both places are located in Himachal Pradesh. The sample includes 405 individuals From Bushahr and 676 individuals from Kinnaur. The results of this study reveal that as the higher altitudes are attained the vital capacity also increases relatively more, and these differences become more pronounced after adolescence, indicating longer time of apnoea. The population living at higher altitudes is also characterised by a significant greater chest length.     

Neuropsychological acclimatization to high altitude

Subjects acclimatized to high altitudes manifest improved manual dexterity as well as trunkal and distal limb co-orbination over un-acclimatized subjects. There is no change in reaction time. Improved attentiveness may contribute to the improved performance, as well as the ability to adapt behaviorally to the numerous physiological consequences of hypoxia. From an ecological and perhaps evolutionary standpoint it matters little whether the adjustment to hypoxia involves intrinsic changes in tissue metabolism (physiological), or results from learning compensatory strategies at altitude (behavioral).     

Plasma gonadotrophins, prolactin and corticosterone concentrations in male mice exposed to high altitude

Groups of sexually-naive male NFR/N mice were maintained at sea level or exposed to simulated altitudes of 18 000 ft (5486 m) or 22 000 ft (6705 m) for 1, 3, 7, 14 or 28 days. Plasma LH concentrations were slightly but not significantly depressed after 1 day of hypoxia. Plasma FSH values were reduced (P < 0.05) after 1, 7, 14 and 28 days of exposure to 22 000 ft when compared to the values in the other groups. Prolactin concentrations fluctuated considerably, but were not uniformly affected by high altitude exposure. Exposure to 18 000 ft resulted in an elevation of plasma corticosterone concentration (P < 0.05) for 3 days, which was followed by a decline to control group values, whereas at 22 000 ft corticosterone levels remained elevated. These findings indicate that plasma LH values are transiently reduced during the initial 24 h of exposure to high altitude and that plasma FSH concentrations are depressed in a sustained manner during severe hypoxia.     

动物对高原低氧的适应性研究进展

本文从血液学、肺动脉、心肺发育及其它方面简要介绍了动物对高原低氧适应的生理、生化及形态学特征,同时也对其中低氧诱导因子的作用及其遗传性方面的研究进行了概述。关于高原低氧适应的遗传机制仍需进一步的深入研究。     

Developmental adaptation to high altitude hypoxia

Experimental studies on animals and humans exposed to hypoxic stress have been reviewed. These data suggest that the influence of hypoxic stress, and the organism's response to it, are greater during growth than during adulthood. The organism's responses include alterations in the quantity and size of the alveolar units of the lungs, enlargement of the right ventricle of the heart, slower somatic growth as measured by birth weight and body size, increased aerobic capacity during maximal work, and greater control of ventilation. It is postulated that the organism is more sensitive to the influence of environmental factors during growth and development than during adulthood. Consequently, adaptive traits acquired during the developmental period have profound, long-term consequences, which are reflected in the physiological and morphological characteristics of the adult organism. It is concluded that the differences between the highland and lowland natives in their physiological performance and morphology are mostly due to adaptations acquired during the developmental period.Attention is called to the fact that the principle of developmental sensitivity and plasticity does not imply equally adaptive responses in all biological parameters. In other words, what we consider a deficiency in a given variable may actually reflect the indirect influence of the adaptive success of another variable.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park Maryland, USA.     

Developmental responses to high altitude hypoxia

From a review of published literature on developmental responses to high altitude, three major conclusions are derived. First, the small birth weight of high altitude native populations are adaptive responses to reduce the oxygen requirements, while the relative increase in the placental weight is a compromise mechanism to increase the volume and surface area for a better oxygenation. Second, the small stature of the high altitude native is due to slow prenatal and postnatal growth. Third, the enlarged chest size, increased lung volumes and predominance of the right ventricle of the heart are due to accelerated development during childhood and adolescence. However, there is not adequate information to determine whether or not the developmental responses of the high altitude native are population-specific, based on a genetic structure different from that of sea level populations. Hence, the need for further study of developmental factors is emphasized.