Effect of temazepam on oxygen saturation and sleep quality at high altitude: randomised placebo controlled crossover trial

Objective: To determine the effects of temazepam on the quality of sleep and on oxygen saturation during sleep in subjects at high altitude.

The Sm domain is an ancient RNA-binding motif with oligo(U) specificity

Sm and Sm-like proteins are members of a family of small proteins that is widespread throughout eukaryotic kingdoms. These proteins form heteromers with one another and bind, as heteromeric complexes, to various RNAs, recognizing primarily short U-rich stretches. Interestingly, completion of several genome projects revealed that archaea also contain genes that may encode Sm-like proteins. Herein, we studied the properties of one Sm-like protein derived from the archaebacterium Archaeoglobus fulgidus and overexpressed in Escherichia coli. This single small protein closely reflects the properties of an Sm or Sm-like protein heteromer. It binds to RNA with a high specificity for oligo(U), and assembles onto the RNA to form a complex that exhibits, as judged by electron microscopy, a ring-like structure similar to the ones observed with the Sm core ribonucleoprotein and the like Sm (LSm) protein heteromer. Importantly, multivariate statistical analysis of negative-stain electron-microscopic images revealed a sevenfold symmetry for the observed ring structure, indicating that the proteins form a homoheptamer. These results support the structural model of the Sm proteins derived from crystallographic studies on Sm heterodimers and demonstrate that the Sm protein family evolved from a single ancestor that was present before the eukaryotic and archaeal kingdoms separated.

Climate change is affecting altitudinal migrants and hibernating species

Calendar date of the beginning of the growing season at high altitude in the Colorado Rocky Mountains is variable but has not changed significantly over the past 25 years. This result differs from growing evidence from low altitudes that climate change is resulting in a longer growing season, earlier migrations, and earlier reproduction in a variety of taxa. At our study site, the beginning of the growing season is controlled by melting of the previous winter's snowpack. Despite a trend for warmer spring temperatures the average date of snowmelt has not changed, perhaps because of the trend for increased winter precipitation. This disjunction between phenology at low and high altitudes may create problems for species, such as many birds, that migrate over altitudinal gradients. We present data indicating that this already may be true for American robins, which are arriving 14 days earlier than they did in 1981; the interval between arrival date and the first date of bare ground has grown by 18 days. We also report evidence for an effect of climate change on hibernation behavior; yellow-bellied marmots are emerging 38 days earlier than 23 years ago, apparently in response to warmer spring air temperatures. Migrants and hibernators may experience problems as a consequence of these changes in phenology, which may be exacerbated if climate models are correct in their predictions of increased winter snowfall in our study area. The trends we report for earlier formation of permanent snowpack and for a longer period of snow cover also have implications for hibernating species.

31P magnetic resonance spectroscopy of the Sherpa heart: a phosphocreatine/adenosine triphosphate signature of metabolic defense against hypobaric hypoxia.

Of all humans thus far studied, Sherpas are considered by many high-altitude biomedical scientists as most exquisitely adapted for life under continuous hypobaric hypoxia. However, little is known about how the heart is protected in hypoxia. Hypoxia defense mechanisms in the Sherpa heart were explored by in vivo, noninvasive 31P magnetic resonance spectroscopy. Six Sherpas were examined under two experimental conditions [normoxic (21% FiO2) and hypoxic (11% FiO2) and in two adaptational states--the acclimated state (on arrival at low-altitude study sites) and the deacclimating state (4 weeks of ongoing exposure to low altitude). Four lowland subjects were used for comparison. We found that the concentration ratios of phosphocreatine (PCr)/adenosine triphosphate (ATP) were maintained at steady-state normoxic values (0.96, SEM = 0.22) that were about half those found in normoxic lowlanders (1.76, SEM = 0.03) monitored the same way at the same time. These differences in heart energetic status between Sherpas and lowlanders compared under normoxic conditions remained highly significant (P < 0.02) even after 4 weeks of deacclimation at low altitudes. In Sherpas under acute hypoxia, the heart rate increased by 20 beats per min from resting values of about 70 beats per min, and the percent saturation of hemoglobin decreased to about 75%. However, these perturbations did not alter the PCr/ATP concentration ratios, which remained at about 50% of the values expected in healthy lowlanders. Because the creatine phosphokinase reaction functions close to equilibrium, these steady-state PCr/ATP ratios presumably coincided with about 3-fold higher free adenosine diphosphate (ADP) concentrations. Higher ADP concentrations (i.e., lower [PCr]/[ATP] ratios) were interpreted to correlate with the Km values for ADP-requiring kinases of glycolysis and to reflect elevated carbohydrate contributions to heart energy needs. This metabolic organization is postulated as advantageous in hypobaria because the ATP yield per O2 molecule is 25-60% higher with glucose than with free fatty acids (the usual fuels utilized in the human heart in postfasting conditions).