Adrenocortical function in rats chronically exposed to high altitude

New Insights into the Genetic Basis of Monge's Disease and Adaptation to High-Altitude

Human high-altitude (HA) adaptation or mal-adaptation is explored to understand the physiology, pathophysiology, and molecular mechanisms that underlie long-term exposure to hypoxia. Here, we report the results of an analysis of the largest whole-genome-sequencing of Chronic Mountain Sickness (CMS) and nonCMS individuals, identified candidate genes and functionally validated these candidates in a genetic model system (Drosophila). We used PreCIOSS algorithm that uses Haplotype Allele Frequency score to separate haplotypes carrying the favored allele from the noncarriers and accordingly, prioritize genes associated with the CMS or nonCMS phenotype. Haplotypes in eleven candidate regions, with SNPs mostly in nonexonic regions, were significantly different between CMS and nonCMS subjects. Closer examination of individual genes in these regions revealed the involvement of previously identified candidates (e.g., SENP1) and also unreported ones SGK3, COPS5, PRDM1, and IFT122 in CMS. Remarkably, in addition to genes like SENP1, SGK3, and COPS5 which are HIF-dependent, our study reveals for the first time HIF-independent gene PRDM1, indicating an involvement of wider, nonHIF pathways in HA adaptation. Finally, we observed that down-regulating orthologs of these genes in Drosophila significantly enhanced their hypoxia tolerance. Taken together, the PreCIOSS algorithm, applied on a large number of genomes, identifies the involvement of both new and previously reported genes in selection sweeps, highlighting the involvement of multiple hypoxia response systems. Since the overwhelming majority of SNPs are in nonexonic (and possibly regulatory) regions, we speculate that adaptation to HA necessitates greater genetic flexibility allowing for transcript variability in response to graded levels of hypoxia.

Hypoxia reduces alveolar epithelial sodium and fluid transport in rats: reversal by beta-adrenergic agonist treatment

In cultured alveolar epithelial cells, hypoxia induces a downregulation of the two main Na proteins, the epithelial Na channel (ENaC) and the Na,K-ATPase. However, the in vivo effects of hypoxia on alveolar epithelial transport have not been well studied. Therefore, the objectives of this study were to investigate in an in vivo rat model if hypoxia induces a reduction in vectorial Na and fluid transport across the alveolar epithelium in vivo, and if a change in net fluid transport is associated with modification in the expression and/or activity of Na transport proteins. Rats were exposed to 8% O(2) from 3 to 24 h. Hypoxia induced a progressive decrease in alveolar liquid clearance (ALC) reaching 50% at 24 h, an effect that was related primarily to a decrease in amiloride-sensitive transepithelial Na transport. On RNase protection assay of alveolar type II (ATII) cells isolated immediately after hypoxic exposure, steady state levels of mRNA were increased for alpha-rENaC and beta(1)-Na, K-ATPase, whereas the levels of gamma-rENaC and alpha(1)-Na,K-ATPase were unchanged. On Western blots of ATII cell membranes, alpha-ENaC subunit protein slightly increased, whereas the amount of alpha(1)- and beta(1)-Na,K-ATPase protein were unchanged with hypoxia. Thus, the decrease in transepithelial Na transport was not explained by a parallel change in gene expression or the quantity of transport proteins. Interestingly, hypoxia-induced decrease in ALC was completely reversed by intra-alveolar administration of the beta(2) agonist, terbutaline (10(-4) M). These results suggest that hypoxia-induced decrease in Na transport is not simply related to a downregulation of Na transport proteins but rather to a decrease in Na protein activity by either internalization of the proteins and/or direct alteration of the protein in the membrane. The dramatic increase of ALC with beta(2)-agonist therapy indicates that the decrease of transepithelial Na and fluid transport during hypoxia is rapidly reversible, a finding of major clinical significance.

Changes in serum protein lipid and electrolyte levels in rabbits at mid-altitude

1. The effects of mid-altitude on the profiles of total serum lipid, cholesterol, fibrinogen, albumin, Ca2+, Cl-, Na+ and K+ were investigated in rabbits for 22 days. From 30 rabbits living at sea level 15 were exposed to 1170 m and 15 to 2240 m altitude. 2. When compared with sea level values; total protein, albumin and K+ significantly decreased up to 5th day (P less than 0.01), then they gradually increased. 3. Total lipid, cholesterol, Ca2+, Cl- and Na+ levels elevated in 2nd day (P less than 0.01) then they gradually decreased to their sea-level values. 4. It was concluded that the adaptation mechanisms begin at mid-altitudes.

The renin-angiotensin-aldosterone system in rats of both sexes subjected to chronic hypobaric hypoxia

Plasma renin activity (PRA), plasmatic aldosterone, haematocrit, haemoglobin concentration and plasma proteins were measured in 36 Wistar rats of both sexes submitted to 380 mmHg in hypopressure chamber during 7 months and in a group of control animals (15 male and 15 female rats). PRA was significantly increased in hypoxic male (P less than 0.05) and female (P less than 0.01) rats. On the contrary, plasma aldosterone concentration did not show any significant variation. There thus was a clear dissociation between the plasmatic renin-angiotensin system and the aldosterone in rats of both sexes submitted to severe chronic hypobaric hypoxia.