Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Sep 2007
Review Historical ArticleRespiratory physiology of high-altitude anurans: 55 years of research on altitude and oxygen.
In a 1951 paper, perhaps the first one addressing adjustments of respiratory physiology in high-elevation anurans, L. C. Stuart tested the hypothesis that hemoglobin values were higher in the high-elevation Bufo bocourti than in the low-elevation species Bufo marinus. ⋯ We start with the early search for evidence of physiological adjustments that took place in the 1960s, move to the studies with Telmatobius that dominated the 1970s and the 1980s, continue with the contributions of experimental physiology that characterized the 1990s, and finish with the discovery of mechanisms enhancing hemoglobin oxygen affinity in high-elevation anurans (2000s). When analyzing the last mentioned topic, we highlight the contributions by the late Professor Carlos Monge, to whom we dedicate this paper. Finally, we discuss the current state of the field, and propose directions for further studies.
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Respir Physiol Neurobiol · Sep 2007
ReviewRole of the peripheral chemoreflex in the early stages of ventilatory acclimatization to altitude.
This review of ventilatory acclimatization to altitude/hypoxia (VAH) emphasizes the widely differing timescales that VAH is considered to encompass. The review concludes: (1) that early (24-48h) VAH is unlikely to arise as a reaction to the respiratory alkalosis that is normally associated with exposure to hypoxia; (2) that changes in peripheral chemoreflex function may be sufficiently rapid to explain early VAH; (3) that alterations in gene expression induced by hypoxia through the hypoxia-inducible factor (HIF) signalling pathway may underlie a major component of VAH; and (4) that compensatory adjustments to acid-base balance in response to the initial respiratory alkalosis may have more significance for the slower changes observed later in VAH.
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Vertebrates at high altitude are subjected to hypoxic conditions that challenge aerobic metabolism. O(2) transport from the respiratory surfaces to tissues requires matching between the O(2) loading and unloading tensions and the O(2)-affinity of blood, which is an integrated function of hemoglobin's intrinsic O(2)-affinity and its allosteric interaction with cellular effectors (organic phosphates, protons and chloride). ⋯ Molecular heterogeneity (multiple isoHbs with differentiated oxygenation properties) can further broaden the range of physico-chemical conditions where Hb functions under altitudinal hypoxia. This treatise reviews the molecular and cellular mechanisms that adapt haemoglobin-oxygen affinities in mammals, birds and ectothermic vertebrates at high altitude.