White Mountain Research Station Research Articles

Chronic Gestational Hypoxia Alters Plasma Exosomal miRNA Profile and Pulmonary Arterial Proteome and Metabolome in Fetal Lambs

Antenatal chronic hypoxia negatively impacts fetal development and increases the risk of cardio-pulmonary dysfunction after birth, including newborn pulmonary hypertension. Previously, we showed that fetal and newborn sheep exposed to chronic hypoxia during gestation exhibit a variety of cardio-pulmonary defects that parallel those of human infants including pulmonary vascular remodeling, heart dysfunction, and pulmonary hypertension. To explore the mechanisms involved in hypoxia-mediated newborn pulmonary hypertension, we test the hypothesis that antenatal chronic hypoxia impairs pathways critical to pulmonary vascular development that are coupled to abnormalities in lung structure and function through dysregulation in cell growth and proliferation. To address this hypothesis, we employed an animal model of pregnant sheep exposed to high altitude hypoxia at the White Mountain Research Station, which has an altitude of 3801 meters. Hypoxic pregnant sheep were housed at altitude during gestation for ~110 days out of 138-141 days of pregnancy while normoxic counterparts were kept at 700 meters. Animals were transferred to Loma Linda at 355 meters and fetal lambs studied at ~140 days of gestation. Fetal plasma samples were collected for exosomal miRNA analysis and pulmonary arteries were collected for proteomic and metabolomic analysis. Ingenuity pathway analysis and other bioinformatic tools were used to interrogate regulatory mechanisms and pathways and the web of molecular interactions affected by hypoxia. Antenatal hypoxic stress caused up and down regulation of a limited number of plasma exosomal miRNAs, pulmonary arterial metabolites and proteins, with discrete interconnections between the various analytes and molecules. There were marked changes in upstream regulators and markers that point to increased oxidative stress and inflammatory response along with pronounced downregulation of matrix proteins and phenotypic markers of vascular smooth muscle cell differentiation. Pathway analyses indicate antenatal chronic hypoxia dysregulates growth and proliferation of vascular cells and impinges on cell migration. While these data require additional study and verification, they provide new insights in the understanding of mechanisms underlying the development of pulmonary hypertension in the newborn following antenatal hypoxia. This work was supported by the National Institutes of Health Grants NIH R01HL155295, R01HL149608, R03HD098477, P01HD083132, and U24DK097154. Additional support was provided by the Loma Linda University School of Medicine, A pilot Project through the West Coast Metabolomics Center, the University of Redlands Summer Research Program, and the Walter E. Macpherson Society. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sierra Skies

White Mountain (37.3803°N, 118.1520°W) is the third tallest peak in California, sitting at 4344 m (14,252 ft). These photos were taken by members of the 2018 SEAWARD altitude research study1 on their way to Barcroft Station, a research laboratory built in 1951 on a lower saddle of the peak at 3798 m (12,470 ft). Barcroft Station is part of University of California Los Angeles’ White Mountain research station and is host to facilities and laboratories for various types of research. It hosted Nobel laureate George Smoot during his research on cosmic background radiation and still serves as the site for current studies on altitude’s effect on human physiology.

Finding Methuselah: New Light on an Old Story

Edmund Schulman is rightly honored for quantifying the age of bristlecone pines and discovering individuals significantly older than giant sequoias (Sequoiadendron gigantea), previously thought to be the oldest living things. However, George Engelmann inferred the potential for great age in his description of bristlecone pine (Pinus aristata) almost a century before, in 1863. Staff from Inyo National Forest re-made Engelmann's inference, and publically asserted that White Mountain bristlecones might outlive giant sequoias before Schulman had published any results of his bristlecone research.Schulman sampled White Mountains pines after seeing a photograph and caption associated with an article by founders of the University of California White Mountain Research Station. Although Schulman's correspondence and publications make this clear, incorrect theories regarding his decision to come to the White Mountains have been published and are promulgated at the Schulman Grove Visitor Center in the White Mountains. This paper places Schulman's work in its historic context by recovering forgotten information about attempts by Inyo National Forest staff and White Mountain Research Station to call attention to the trees. It also recovers details of Schulman's and C. Wesley Ferguson's activities in the White Mountains range as documented in field notes and Thomas Harlan's Bristlecone Pine Project database.

Long Term Hypoxia Reduces Antioxidant Levels and Causes a Glycolytic Shift in Neonatal Sheep Pulmonary arteries

Gestational Hypoxia is a common prenatal stress caused by high altitude living, smoking, and other prenatal disorders. Such hypoxic insult can cause abnormalities in lung development that result in pulmonary hypertension in the newborn. Hypoxia is known to cause oxidative stress and accentuate glycolysis in adult tissues, effects which are intertwined with the development of various diseases. However, the adaptive responses of metabolism to long term hypoxia (LTH) in the fetal pulmonary vasculature is not nearly as well understood. The current work tests the hypothesis that following gestational LTH there is reduced antioxidant capacity and increased cellular glycolysis in neonatal sheep. For this study, normoxic pregnant and non‐pregnant sheep were obtained from Nebeker Ranch in Lancaster, CA (~700 meters) and were either sent to Loma Linda for study or to the White Mountain Research Station at an altitude of 3800 meters to induce LTH. After 110+ days at high altitude, animals were transported to Loma Linda University for the study. Pulmonary arteries of adult, 2‐week‐old newborn, and near‐term fetal sheep were isolated and frozen for analysis of primary metabolites. Metabolite levels were analyzed using Gas Chromatograph Time of Flight mass spectrometry (GC‐TOF MS) and visualized using enrichment and pathway analyses. LTH decreased the concentration of the antioxidant glutathione (GSH) and increased lactic acid, a byproduct of glycolysis, in adult and fetus. In the newborn LTH also decreased citric acid, a key intermediate in the Krebs cycle. These data indicate that the mother does not protect the pulmonary vasculature of the fetus from long term hypoxic stress due to gestation at high altitude. Thus, the fetus appears to be vulnerable even at modest altitudes to metabolic shifts and oxidative stress. Effects of these metabolic changes may persist after birth and contribute to the development of disease in the neonate or later in life.Support or Funding InformationThis material is based upon work supported by NIH grants P01HD083132 (LZ) and 1U24DK097154 through a pilot project grant to SMW as well as P20MD006988. IK was an Undergraduate Summer Research Fellow while RA was an Apprenticeship Bridge to College Scholar through the Center for Health Disparities and Molecular Mechanisms at Loma Linda University. VL is a recipient of the American Physiological Society's Short‐Term Research Education Program to Increase Diversity in Health‐Related Research (STRIDE) Fellowship funded by the APS and a grant from the National Heart, Lung and Blood Institute R25HL115473.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California

Research Article| July 01, 2013 Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California Colin B. Amos; Colin B. Amos † 1Geology Department, Western Washington University, Bellingham, Washington 98225, USA †E-mail:Colin.Amos@wwu.edu Search for other works by this author on: GSW Google Scholar Sarah J. Brownlee; Sarah J. Brownlee 2Department of Geology, Wayne State University, Detroit, Michigan 48202, USA Search for other works by this author on: GSW Google Scholar Dylan H. Rood; Dylan H. Rood 3Accelerator Mass Spectrometry Laboratory, Scottish Universities Environmental Research Centre (SUERC), East Kilbride G75 0QF, UK4Earth Research Institute, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar G. Burch Fisher; G. Burch Fisher 5Department of Earth Science, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Roland Bürgmann; Roland Bürgmann 6Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Paul R. Renne; Paul R. Renne 7Berkeley Geochronology Center, Berkeley, California 94709, USA Search for other works by this author on: GSW Google Scholar Angela S. Jayko Angela S. Jayko 8U.S. Geological Survey, U.C. White Mountain Research Station, Bishop, California 93514, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2013) 125 (7-8): 1187–1202. https://doi.org/10.1130/B30803.1 Article history received: 06 Oct 2012 rev-recd: 05 Mar 2013 accepted: 30 Mar 2013 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Colin B. Amos, Sarah J. Brownlee, Dylan H. Rood, G. Burch Fisher, Roland Bürgmann, Paul R. Renne, Angela S. Jayko; Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California. GSA Bulletin 2013;; 125 (7-8): 1187–1202. doi: https://doi.org/10.1130/B30803.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract New geochronologic and geomorphic constraints on the Little Lake fault in the Eastern California shear zone reveal steady, modest rates of dextral slip during and since the mid-to-late Pleistocene. We focus on a suite of offset fluvial landforms in the Pleistocene Owens River channel that formed in response to periodic interaction with nearby basalt flows, thereby recording displacement over multiple time intervals. Overlap between 40Ar/39Ar ages for the youngest intracanyon basalt flow and 10Be surface exposure dating of downstream terrace surfaces suggests widespread channel incision during a prominent outburst flood through the Little Lake channel at ca. 64 ka. Older basalt flows flanking the upper and lower canyon margins indicate localization of the Owens River in its current position between 212 ± 14 and 197 ± 11 ka. Coupled with terrestrial light detection and ranging (lidar) and digital topographic measurements of dextral offset, the revised Little Lake chronology indicates average dextral slip rates of at least ∼0.6–0.7 mm/yr and <1.3 mm/yr over intervals ranging from ∼104 to 105 yr. Despite previous geodetic observations of relatively rapid interseismic strain along the Little Lake fault, we find no evidence for sustained temporal fluctuations in slip rates over multiple earthquake cycles. Instead, our results indicate that accelerated fault loading may be transient over much shorter periods (∼101 yr) and perhaps indicative of time-dependent seismic hazard associated with Eastern California shear zone faults. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Year in review 2010: Interstitial lung diseases, acute lung injury, sleep, physiology, imaging, bronchoscopic intervention and lung cancer

Year in review 2010: Interstitial lung diseases, acute lung injury, sleep, physiology, imaging, bronchoscopic intervention and lung cancer

Monitoring for potential effects of climate change on the vegetation of two alpine meadows in the White Mountains of California, USA

East Shield (3658 m) and Barcroft Gate (3697 m) Meadows in the White Mountains of California on the Inyo National Forest were selected for a pilot baseline monitoring study over five-year intervals to determine potential effects of future climate change on the meadows. Stated as a hypothesis: given the natural range of temporal variability of meadow vegetation, a significant portion of that variability is attributed to the effects of climatic variation. The study is associated with the Global Observation Research Initiative in Alpine Environments Project (GLORIA) hosted by the University of California White Mountain Research Station. Both meadows are sedge–rush–grass wet meadows, or fens, which are sustained by surface water in the form of streams and springs. A comprehensive plant list was compiled and the plant species of each meadow were sampled by a point intercept method along two randomly placed transects. The occurrence of all species at predetermined one-meter interval sample points along the transects were recorded, percent occurrence was calculated, and descriptive statistics were done. The monitoring objective is to detect a 20% biologically meaningful change in the vegetation over time with 90% confidence, and accept a 10% chance of a false change error (Type 1 error). Monitoring is planned to be done in conjunction with tracking change in precipitation and temperature. Three indicators of possible climate change were chosen. One indicator is increase in the abundance of those species whose upper range is at or below meadow elevations. The rationale for this indicator is based the 2007 IPCC report estimation that a doubling of atmospheric CO 2 will increase global temperature with a best estimate of +3.0 °C. Assuming that the present general lapse rate of −6.32 °C per kilometer for the White Mountains will persist, a 3.0 °C increase may result in an equivalent elevation of the meadows of about +475 m. Published elevation ranges indicate that most recorded species are not likely to be affected by the estimated temperature increase. Second and third indicators are a shift in cover from wet meadow to dry meadow species, and the presence and increase of shrub species resulting from postulated reduced precipitation with drying of meadows and encroachment by surrounding shrubs (sagebrush and rabbitbrush). This monitoring study has the potential to detect long-term responses of vegetation to climate change, and reduce uncertainties and confirm or correct the expected consequences of temperature change.

BIRTH ALTITUDE AFFECTS AEROBIC PERFORMANCE

High altitude rarefied atmospheres can come as a shock if you're used to life at sea-level. No matter how hard you breathe, initially you're left gasping. However, given time, most species adjust to the new conditions. Gregory Russell from the University of California at Riverside explains that animals living at altitude tend to have larger hearts and lungs than their sea-level relatives. Yet despite this advantage, they don't always perform better than mice living at lower altitudes, possibly due to low oxygen levels limiting the animal's aerobic performance. Which made Russell, Enrico Rezende and Kimberly Hammond wonder how much of an effect developmental history has on an animal's ability to cope with different oxygen levels. The team decided to see how the aerobic performance of adult deer mice was affected by the oxygen level and altitude of their birth(p. 35).With access to a lab-based colony of deer mice, Russell transported twenty mouse pairs to 3800 m altitude at the White Mountain Research Station ready to see how their high-born young faired relative to low-born mice. At 5 weeks of age, Russell put each of the high- and low-altitude-born mice in a treadmill and measured their aerobic performances. Then he artificially reduced the oxygen levels in the treadmill for the low-altitude mice (to simulate the effects of hypoxia at high altitude) and increased the oxygen for the high-altitude mice (simulating the effects of normoxia at low altitude) to see how they faired. The animals born in low oxygen (hypoxia) at high altitude out-performed the mice born in high oxygen (normoxia) at low altitude. At 5 weeks of age it seemed as if being born at high altitude had given the mice an advantage over the low-altitude pups.So how would the pups born at high and low altitude adjust when transported to the opposite situation? Russell carefully transported half of the 5-week-old high-altitude pups down to the Riverside labs, and half of the Riverside pups up to the mountains, leaving the other two groups at their birth places. Giving the relocated animals 8 weeks to acclimate to their new environment, Russell again tested all of the animals' aerobic performances in response to hypoxia and normoxia.Amazingly, pups born at low altitude (normoxia) outperformed all of the other mice after a period of acclimation to high altitude, while the performance of pups born at high altitude (hypoxia) changed little or declined after remaining at altitude or acclimating at low altitude. The team realised that when they had tested the 5-week-old animals, the high-altitude pups must have already acclimated to the hypoxic conditions. And when the team analysed the animals' aerobic performances, it became clear to them that there must be a physiological difference between pups gestated and born at high altitude,and pups born at low altitude. `How the mice accommodate the challenges imposed by high altitude depends on where they are born' says Russell. `We don't know how they do it', he adds `but suspect that high-altitude mice acclimate in a different way'.

Angular power spectrum of the fastica cosmic microwave background component from Background Emission Anisotropy Scanning Telescope data

We present the angular power spectrum of the cosmic microwave background (CMB) component extracted with FASTICA from the Background Emission Anisotropy Scanning Telescope (BEAST) data. BEAST is a 2.2-m off-axis telescope with a focal plane comprising eight elements at Q (38‐45 GHz) and Ka (26‐36 GHz) bands. It operates from the UC (University of California) White Mountain Research Station at an altitude of 3800 m. The BEAST CMB angular power spectrum has already been calculated by O’Dwyer et al. using only the Q-band data. With two input channels, FASTICA returns two possible independent components. We found that one of these two has an unphysical spectral behaviour, while the other is a reasonable CMB component. After a detailed calibration procedure based on Monte Carlo (MC) simulations, we extracted the angular power spectrum for the identified CMB component and found a very good agreement with the already published BEAST CMB angular power spectrum and with the Wilkinson Microwave Anisotropy Probe (WMAP) data.

A strategy for determining arterial blood gases on the summit of Mt. Everest

BackgroundClimbers on the summit of Mt. Everest are exposed to extreme hypoxia, and the physiological implications are of great interest. Inferences have been made from alveolar gas samples collected on the summit, but arterial blood samples would give critical information. We propose a plan to insert an arterial catheter at an altitude of 8000 m, take blood samples above this using an automatic sampler, store the samples in glass syringes in an ice-water slurry, and analyze them lower on the mountain 4 to 6 hours later.ResultsA preliminary design of the automatic sampler was successfully tested at the White Mountain Research Station (altitude 3800 m – 4300 m). To determine how much the blood gases changed over a long period, rabbit blood was tonometered to give a gas composition close to that expected on the summit (PO2 4.0 kPa (30 mmHg), PCO2 1.3 kPa (10 mmHg), pH 7.7) and the blood gases were measured every 2 hours for 8 hours both at sea level and 3800 m. The mean changes were PO2 +0.3 to +0.4 kPa (+2 to +3 mmHg), PCO2 0 to +0.13 kPa (+1 mmHg), pH -0.02 to -0.04, base excess -0.7 to -1.2 mM. In practice the delay before analysis should not exceed 4 to 6 hours. The small paradoxical rise in PO2 is presumably caused mainly by contamination of the blood with air.ConclusionWe conclude that automatic arterial blood sampling at high altitude is technically feasible and that the changes in the blood gases over a period of several hours are acceptably small.

An astronomical site survey at the Barcroft Facility of the White Mountain Research Station

We present a distillation of weather and sky condition data collected from September 2001 to November 2004 at the University of California White Mountain Research Station, Barcroft Facility. Our conclusion is that Barcroft is an excellent site for microwave observation because of a cold microwave zenith temperature, low precipitable water, and a high percentage of clear days. The solar intensity was above 80% of the theoretical maximum 66% of the time. About 71% of the daytime, the cloud cover was acceptable for observing. Median precipitable water vapor was estimated to be 1.75mm. We measure a median opacity at 225GHz of 0.11, which corresponds to a transmission of 89.6%. Zenith sky temperatures were determined to be 9.0±0.2K and 10.0±0.6K in Q-band (38–46GHz) and W-band (81–98GHz), respectively. We also demonstrate a correlation between measurements of precipitable water vapor from a weatherstation and a 225GHz radiometer.

A Map of the Cosmic Microwave Background from the BEAST Experiment

We present the first sky maps from the BEAST (Background Emission Anisotropy Scanning Telescope) experiment. BEAST consists of a 2.2 m off-axis Gregorian telescope fed by a cryogenic millimeter wavelength focal plane currently consisting of six Q band (40 GHz) and two Ka band (30 GHz) scalar feed horns feeding cryogenic HEMT amplifiers. Data were collected from two balloon-borne flights in 2000, followed by a lengthy ground observing campaign from the 3.8 km altitude University of California White Mountain Research Station. This paper reports the initial results from the ground-based observations. The instrument produced an annular map covering the sky over 33? < ? < 42?. The maps cover an area of 2470 deg2 with an effective resolution of 23' FWHM at 40 GHz and 30' at 30 GHz. The map rms (smoothed to 30' and excluding Galactic foregrounds) is 57 ? 5 ?K (Rayleigh-Jeans) at 40 GHz. Comparison with the instrument noise and correcting for 5% atmospheric attenuation gives a cosmic signal rms contribution of 29 ? 3 ?K (R-J) or 30 ? 3 ?K relative to a Planck blackbody of 2.7 K. An estimate of the actual cosmic microwave background (CMB) sky signal requires taking into account the l space filter function of our experiment and analysis techniques, carried out in a companion paper. In addition to the robust detection of CMB anisotropies, we find a strong correlation between small portions of our maps and features in recent H? maps. In this work we describe the data set and analysis techniques leading to the maps, including data selection, filtering, pointing reconstruction, mapmaking algorithms, and systematic effects.

The δ17O and δ18O measurements of atmospheric sulfate from a coastal and high alpine region: A mass‐independent isotopic anomaly

Atmospheric sulfate extracted from rainwater and aerosols has been sampled from two environments: La Jolla and White Mountain Research Station (WMRS), California. In general, the multiple stable oxygen isotopic analysis of these sulfate samples shows that they possess mass‐independent oxygen isotopic compositions, unlike laboratory nonatmospheric standards. As suggested by the recent laboratory findings, the source of mass independent oxygen isotopic composition in sulfate is implied to be aqueous phase S(IV) oxidation by atmospheric H2O2 and O3. The relative S(IV) oxidation contribution by H2O2 and O3, which together generally represent the overall aqueous phase S(IV) oxidation, is estimated utilizing the average 17O enrichment value of La Jolla rainwater sulfate samples as an index. The estimate indicates a relative dominance of the aqueous over gas phase S(IV) oxidation. Although inconclusive owing to small data sets, both La Jolla and WMRS aerosol sulfate samples display seasonal 17O enrichment variations with a maximum in winter and a minimum in summer. Such seasonal isotopic variations are believed to derive from climatic effects that favor aqueous phase S(IV) oxidation in winter compared to summer. The radioactivity measurements of the cosmogenic 35S radionuclide, coupled with double oxygen isotope ratio measurements suggests an atmospheric sulfate contribution from high‐altitude air mass (perhaps stratospheric) at WMRS, in particular during late winter/early spring season. The results of this work provide a new way to quantify relative oxidative pathways of S(IV) species in the atmosphere and to improve understanding atmospheric processes associated with sulfate.

Intermittent vs continuous hypoxia: effects on ventilation and erythropoiesis in humans

Recently, we showed that 5 days of normobaric intermittent hypoxia at rest (IH; 2 hours daily at 3,800 m simulated altitude; partial pressure of inspired oxygen 90 torr) can induce an increase in the isocapnic hypoxic ventilatory response (HVR) and blood reticulocyte count. The purpose of the present study was to compare these data with continuous exposure to the same hypoxic level. Four of the same subjects were exposed, a year later, to 2 days of continuous hypoxia (CH), and 4 different subjects were exposed to 8 weeks of CH, both at the White Mountain Research Station (3,800 m altitude, barometric pressure approximately 489 torr). Inspired minute ventilation (VI), end-tidal partial pressure of carbon dioxide, arterial oxygen saturation (SaO2[sat]), hematocrit, and hemoglobin concentration were measured at different times during the continuous exposures. The HVR was expressed as the increase in V1 per 1% decrease in SaO2. The HVR showed no significant difference in the control values 1 year apart (IH, 0.06 +/- 0.03; CH2d (2 days' continuous hypoxia), 0.19 +/- 0.07 L x min(-1) x %sat(-1); means +/- SE), and the HVR values were similar after 2 days of IH compared to CH (0.42 +/- 0.26 and 0.51 +/- 0.22 L x min(-1) x %sat(-1), respectively). On the new subjects after 2 weeks of CH, the HVR showed a maximum increase, similar to the increase observed after only 5 days of IH, hemoglobin concentrations and hematocrit were significantly increased (45.0 +/- 2.7% vs 51.5 +/- 3.0% and 14.5 +/- 0.7 vs 17.2 +/- 1.0 g x dL(-1), respectively). The HVR did not change significantly from week 2 to 8 of CH, whereas hematological data were still increasing at the end of the 8 weeks. Changes in ventilatory oxygen sensitivity induced by IH and CH are similar in magnitude but occur with different time courses. The effects of IH on erythropoiesis are significant but fewer than on CH.

The 18O/16O and 17O/16O ratios in atmospheric nitrous oxide: A mass-independent anomaly

Measurements of the oxygen isotope ratios (18O/16O and 17O/16O) in atmospheric nitrous oxide (N2O) from La Jolla, Pasadena, and the White Mountain Research Station (elevation, 3801 meters) in California and the White Sands Missile Range in New Mexico show that N2O has a mass-independent composition. These data suggest the presence of a previously undefined atmospheric process. The La Jolla samples can be explained by a mixing between an atmospherically derived source of mass-independent N2O and biologically derived mass-dependent N2O. Possible origins of the mass-independent anomaly in N2O are discussed.

Term ovine placental vasculature: Comparison of sea level and high altitude conditions by corrosion cast and histomorphometry

The placental vascular architecture differs significantly at high altitude from that at sea level in the human and guinea-pig. Four sheep between 137 and 140 days of gestation, kept near sea level throughout gestation, were used as a normoxic control group for comparison of the placental vasculature with 10 other ewes, kept at high altitude (3820 m above sea level; Barcroft Laboratory, White Mountain Research Station, CA, USA). Placentomes from both groups were prepared for histology and scanning electron microscopy of vascular corrosion casts. Singular perfusion of fetal placentae, as well as combined maternal/fetal injection was performed. The influence of long-term hypoxaemia was determined by qualitative and semi-quantitative evaluation of corrosion casts and histological sections. The fetal vessel casts show a distinct difference in the arrangement of vessels of all sizes in response to long-term hypoxaemia. In the control group, stem arteries and veins are straight and parallel. In contrast, this is much less evident in the hypoxaemic group because arterioles and venules branch off the stem vessels more frequently and in an irregular manner. This leads to a capillary bed that is much more dense due to increased branching and capillary coiling. These observations are confirmed by histomorphometry. In the fetal vessels of high altitude sheep placentomes, we observed a decreased number of vascular cross sections (21.6 ± 4.7 sem versus 27.7 ± 4.0 sem; P=0.02). However, the average luminal size per cross section (77.9 ± 10.5 μm 2 sem versus 59.4 ± 7.4 μm 2 sem; P=0.004) was increased at high altitude and the percentage of lumina of the total area (5.7 ± 0.5 sem versus 5.3 ± 0.3 sem; P=0.09) indicated a trend towards an increase. In maternal vessels of high altitude placentomes, the number of vessel cross sections (6.5 ± 0.7 sem versus 6.0 ± 0.5 sem; P=0.2) remained unchanged, whereas the average luminal size (1108 ± 122 μm 2 sem versus 844 ± 77 μm 2 sem; P < 0.001) and the percentage of lumina out of the tot area (20.9 ± 1.8 sem versus 17.5 ± 1.7 sem; P<0.001) were increased. The interhaemal distance appeared to be slightly but not significantly increased at high altitude. These findings indicate that at high altitude the sheep placenta develops an increased materno-fetal absorptive surface to help guarantee substance exchange.

A liquid-helium-cooled absolute reference cold load for long-wavelength radiometric calibration

We describe a large (78 cm) diameter liquid-helium-cooled blackbody absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid-helium (LHe) boiling point, with total uncertainty in the radiometric temperature of less than 30 mK over the 2.5–23-cm wavelength (12–1.3 GHz) operating range. Emission from those parts of the cold load not immersed in LHe is ≤25 mK and the reflection coefficient is ≤3.5×10−4. This cold load has been used at several wavelengths at the South Pole, Antarctica and at the White Mountain Research Station, California to calibrate spectral measurements of the cosmic microwave background radiation. For the instruments operated at 20-, 12-, 7.9-, and 4.0-cm wavelength at the South Pole, the total corrections to the LHe boiling-point temperature (∼3.8 K) were 48±23, 18±10, 10±18, and 15±16 mK, respectively. In operation, the average LHe loss rate was ≤4.4 ℓ/h, allowing day-long periods of operation without a LHe fill. The boiloff rate is not strongly dependent on the radiative load at the aperture, yielding very stable operation and radiometric performance. Design considerations, radiometric and thermal performance, and operational aspects are discussed. A comparison with other LHe-cooled reference loads including the predecessor of this cold load is given.

Simultaneous measurements of atmospheric emissions at 10, 33, and 90 GHz

As part of a larger experiment to measure the cosmic microwave background radiation spectrum, frequent simultaneous measurements of microwave thermal emissions from the earth's atmosphere have been made at 10, 33, and 90 GHz. We have performed these measurements at two separate locations, Berkeley, California, and the White Mountain Research Station located near Bishop, California, which differ greatly in altitude and climatic conditions. Typical values of the atmospheric antenna temperature measured in Berkeley (250‐m elevation) during good weather are 2.54±0.29, 12.4±0.3, and 34.3±0.5 K for 10, 33, and 90 GHz, respectively. Corresponding values measured at White Mountain (3800 m) are 1.11± 0.04, 4.48±0.18, and 11.0±0.1 K. Because the measurements are simultaneous in nature, correlations between the measurements taken at the various frequencies provide constraints on models of the microwave emission of the earth's atmosphere, especially models describing atmospheric emission as a function of precipitable water content.

The Pathophysiology of Chronic Hypoxia in Chickens

The debilitating effects of the hypoxia encountered at high altitude have been recognized for many hundreds of years, and have recently been the subject of numerous scientific investigations (8,9). Prolonged residence at high altitude leads to characteristic anatomic and physiological alterations (4,8), as well as special pathophysiological conditions such as "Brisket Disease" in cattle (3). The domestic fowl is particularly suited to studies of the pathophysiology of chronic hypoxia. Since it is the most sensitive of small homeotherms to hypoxia (1), effects may be rather severe at mountain altitudes.c Because of their ovipary, colonies of chickens can be maintained at reasonably high elevations by carrying out incubation (i.e., embryogenesis, the process most sensitive to hypoxia) at lesser and more suitable elevations. In 1955, a colony of Single Comb White Leghorn (SCWL) chickens was established at an elevation of 12,500 feet, at the White Mountain Research Station," with week-old chicks introduced from sea level. In 1956, a few of the chickens were sacrificed to determine the cause of a persistent mortality among adults. No evidence of contagious disease was encountered; however, there were obvious heart lesions and signs of chronic circulatory insufficiency. More detailed examinations were made in 1960, 1962, and 1964, and the results are reported herein.

Alpine Vegetation and Active Frost Features of Pellisier Flats, White Mountains, California

Active, polar-type frost features are described from a high plateau in the White Mountains, a range which flanks the Great Basin along the California-Nevada state line. Observations of unusual vegetation patterns and of plant remains in overridden turf banks are presented; these, as well as other data support the idea that a current, annual, freeze-thaw cycle contributes to soil heaving and instability on the large solifluction terraces of the region. The flora of Pellisier Flats is listed for the first time, and the distribution of species is presented in tabular form to show the relationships of the floral components to frost scars and the gross topography of this remote area. INTRODUCTION Pellisier Flats is the gently rolling, north-trending plateau that forms the crest of California's White Mountains in the region near the Nevada state line (Fig. 1). This nearly inaccessible2 eight-squaremile surface ranges from 12,500 to 13,500 ft (4100-4430 m) in altitude. It lies 8,000 ft ablove the flanking desert basins and 1,000 to 2,000 ft above upiper tree line. The plateau (Fig. 2) is bounded on the west by precipitous canyons, which drain into the Owens Vallev, and on the east by sheer-walled glacial cirques, which expand into broad valleys. During the summer of 1964 the authors traversed Pellisier Flats to collect and catalogue the flora and to make geological observations; the presence of apparently active frost features and corresponding zonation of the vegetation led to subsequent investigations. CLIMATE The climate at 12,500 ft (4100 m) in the White Mountains is cold and semiarid (K6ppen Bsk) as indicated by the weather records of the Barcroft Laboratory of the White Mountain Research Station, located 10 miles south of the flats (Pace, 1963). Yearly precipitation is 15.5 inches, the mean annual temperature 28 F. Although precipitation is mostly in the form of winter snows, occasional summer thunderstorms, bring heavy rains. The habitat classification appropriate for most of the flats is that of alpine fell-field. 1 Two of the authors (Lloyd and Mitchell) were employed by the White Mountain Research Laboratories of the University of California during the summers of 1963-1965 to engage in a study of the White Mountains flora. 2 Helicopter service was furnished by the White Mountain Research Station. 516 This content downloaded from 207.46.13.111 on Sat, 08 Apr 2017 19:50:16 UTC All use subject to http://about.jstor.org/terms 1966 MITCHELL ET AL.: PELLISIER FLATS 517 Boundory P44k a 13140 fISH