PubMed · 6364164
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C S Houston. 1983. D. Bruce Dill.. https://pubmed.ncbi.nlm.nih.gov/6364164/
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Pulmonary hypertension is a well-recognised condition in dogs, and, among other mechanisms, is caused by hypoxia. In order to evaluate the effect of chronic hypobaric hypoxia on pulmonary arterial pressure in dogs, a colony of 19 clinically and biochemically healthy Greenland sled dogs living permanently at at least 2300 m above sea level (altitude dogs) and 10 clinically healthy Greenland sled dogs living at 700 to 900 m above sea level (control dogs) were examined. Investigations were made of the dogs' packed-cell volume, venous and arterial blood gases, electrocardiogram, blood pressure and echocardiograph, including the calculation of pulmonary arterial pressure by Doppler examination of tricuspid regurgitation. The altitude dogs had a marked arterial hypoxaemia with a mean (sd) oxygen partial pressure of 61.9 (7.4) mmHg and a significantly lower arterial oxygen saturation (90.7 [3.7] per cent) than the control dogs (96.7 [0.8] per cent). In eight of the altitude dogs, tricuspid regurgitation allowed calculation of the systolic pulmonary arterial pressure, which was 29.5 (10.4) mmHg. Eight of the control dogs had tricuspid insufficiency, and their derived systolic pulmonary arterial pressure was significantly lower (17.4 [3.9] mmHg).
Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assemblages, although field evidence for this is rarely presented. The study was based on a survey of 29 Pyrenean lakes with altitudes ranging between 1,875 and 2,990 m carried out during July and August 2000. Because of the oligotrophic nature of these lakes, we aimed to confirm that food partitioning is a major factor in shaping zooplankton assemblages. We analysed the amino acid composition of six cladocera and seven copepod species. A discriminant analysis showed that each species could be distinguished according to its amino acid composition. A negative relationship between amino acid differentiation and co-occurrence among the cladocera and cyclopoid copepod was observed. In contrast, calanoids did not show any relationship and were characterised by a high amino acid differentiation between species. As the differences in the amino acid composition among zooplankton species indicate distinct food sources, the relationship found indicates that trophic-niche differentiation plays a key role in determining the assemblage of these zooplankton communities. Therefore exploitative competition, either at present or in the past by driving co-evolutionary histories, has been a significant factor in structuring the cladocera and cyclopoid communities in these oligotrophic lakes.
Ischemic hypoxia provokes alterations in the production system of nitric oxide in the cerebellum. We hypothesize that the nitric oxide system may undergo modifications due to hypobaric hypoxia and that may play a role in high altitude pathophysiology. Therefore, changes in the nitric oxide system of the cerebellum of rats submitted to acute hypobaric hypoxia were investigated. Adult rats were exposed for 7 h to a simulated altitude of 8235 m (27000 ft.) and then killed after 0 h or 1, 3, 5 and 10 days of reoxygenation. Nitric oxide synthase calcium-dependent and -independent activity, immunoblotting and immunohistochemistry of neuronal, endothelial, and inducible nitric oxide synthase, and nitrotyrosine were evaluated. Immunoreactivity for neuronal nitric oxide synthase slightly increased in the baskets of the Purkinje cell layer and in the granule cells, after 0 h of reoxygenation, although no changes in neuronal nitric oxide synthase immunoblotting densitometry were detected. Calcium-dependent activity significantly rose after 0 h of reoxygenation, reaching control levels in the following points, and being coincident with a peak of eNOS expression. Nitrotyrosine formation showed significant increments after 0 h and 1 day of reoxygenation. Nitrotyrosine immunoreactivity showed an intracellular location change in the neurons of the cerebellar nuclei and in addition, an appearance of nitration in the soma of the Purkinje cells was detected. No changes in inducible nitric oxide synthase activity, immunoblotting or immunohistochemistry were detected. We conclude that at least part of the nitric oxide system is involved in cerebellum responses to hypobaric hypoxia.