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Query: UMLS:C0242706 (hyperoxia)
 5,219 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A variation on the classic ablation method was used to determine whether O(2) uptake or ionoregulation is the first to shift from the skin to the gills in developing zebrafish, Danio rerio. Zebrafish larvae, ranging in age from 3 to 21 days postfertilization, were prevented from ventilating their gills and forced to rely on cutaneous processes by exposing them to one of two anaesthetics (tricaine methanesulphonate or phenoxyethanol) or by embedding their gills in agar. They were then placed in solutions designed to compensate selectively for impaired O(2) uptake (42% O(2)), impaired ionoregulatory capacity (50% physiological saline) or impairment of both functions (42% O(2)+50% physiological saline). Survival under these conditions was compared with that in normoxic (21% O(2)) fresh water. Neither hyperoxia nor 50% physiological saline had any significant effect on the survival of newly hatched larvae (3 days postfertilization), suggesting that at this stage cutaneous exchange was sufficient to satisfy both ionoregulatory and respiratory requirements. At 7 days postfertilization, the skin still appeared capable of satisfying the O(2) requirements of larvae but not their ionoregulatory requirements. Physiological saline significantly improved survival at 7 days postfertilization; hyperoxia did not. At 14 days postfertilization, both hyperoxia and 50% saline significantly improved survival, indicating that at this stage gills were required for O(2) uptake as well as for ionoregulation. At 21 days postfertilization, only hyperoxia significantly improved survival. By this stage, larvae apparently are so dependent on gills for O(2) uptake that they suffocate before the effects of ionoregulatory impairment become apparent. Thus, it would appear that in zebrafish it is the ionoregulatory capacity of the skin not its ability to take up O(2) that first becomes limiting. This raises the possibility that ionoregulatory pressures may play a more important role in gill development than is generally appreciated.
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PMID:Gills are needed for ionoregulation before they are needed for O(2) uptake in developing zebrafish, Danio rerio. 1204 37

Pulmonary oxygen toxicity is a dose-dependent effect on alveolar epithelial and endothelial cells resulting in pulmonary oedema. Any concomitant effects on systemic capillary endothelium would be expected to result in capillary leakage and an increase in the tissues' water content. Total tissue water (TTW) in different organs was therefore studied in freely moving rats exposed to 100% O2 at normobaric pressure for 24 or 48 h, and compared to air-breathing control rats. The TTW for the following tissues was measured: Trachea, left bronchus, left lung, left and right ventricle, left kidney, skin (left paw-hindlimb), skin (back of the rat), left brain, left eye and thigh muscle left side. There was a significant increase in TTW of the lung accompanied by pleural effusion after 48 h of oxygen exposure as expected in all exposed animals. There was a small increase in TTW of the paw only, and a small decrease or no change in other tissues after 24 and 48 h of exposure. We conclude that there is no evidence of systemic capillary dysfunction as measured by tissue water content after exposure to hyperoxia in a dosage causing pulmonary oedema.
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PMID:Effects of normobaric hyperoxia on water content in different organs in rats. 1219 14

The effects of intracellular pH (pH(i)), paramagnetic macroscopic, and microscopic susceptibility on T(1) in the rotating frame (T(1rho)) were studied in rat brain. Intracellular acidosis was induced by hypercapnia and pH(i), T(1rho), T(2), diffusion, and cerebral blood volume (CBV) were quantified. Taking into account the CBV contribution, a prolongation of parenchymal T(1rho) by 4.5% was ascribed to a change in tissue water relaxation caused by a one unit drop in pH(i). Blood T(1rho) was found to prolong linearly with blood oxygenation saturation (Y). The macroscopic susceptibility contribution to parenchymal T(1rho) was assessed both through BOLD and an iron oxide contrast agent, AMI-227. The T(1rho) data from these experiments could be described by intravascular effects with insignificant effects of susceptibility gradients on tissue water. Tissue oxygen tension (PtO(2)) was manipulated and monitored with microelectrodes to assess its plausible contribution to microscopic susceptibility and relaxation. Parenchymal T(1rho) was virtually unaffected by variations in the PtO(2), but T(1) was shortened in hyperoxia and T(2) showed a negative BOLD effect in hypoxia. It is demonstrated that pH(i) directly modulates tissue T(1rho), possibly through its effect on proton exchange; however, neither BOLD nor PtO(2) directly influence tissue T(1rho). The observations are discussed in the light of physicochemical mechanisms contributing to the ischemic T(1rho) changes.
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PMID:Effects of intracellular pH, blood, and tissue oxygen tension on T1rho relaxation in rat brain. 1221 Sep 11

The hypothesis that postnatal nicotine exposure weakens cardiorespiratory recovery from reflex apnea and bradycardia was tested in eight lambs continuously infused with nicotine from the day of birth at a dose of 1 to 2 mg.kg(-1).d(-1). Eight age-matched lambs infused with saline served as controls. Apnea and bradycardia were elicited by laryngeal stimulation with 1 mL of water (laryngeal chemoreflex) both during air breathing [0.21 fraction of inspired oxygen (FiO(2))] and mild hypoxia (0.10 FiO(2)) at a mean postnatal age of 5 +/- 1, 14 +/- 1, and 28 +/- 1 d. Ventilation, heart rate, and blood pressure were similar in the two groups at rest. In response to laryngeal chemoreflex stimulation, nicotine-treated lambs had a more pronounced decrease in ventilation (p < 0.05), longer reflex apnea (p < 0.001 in 0.21 FiO(2); p < 0.01 in 0.10 FiO(2)), and greater reflex bradycardia (p < 0.01). During reflex apnea, sighs were less efficient in restoring heart rate to prestimulation level, and a greater decrease in heart rate was observed before sighs in nicotine-treated lambs. These effects were most apparent at 5 d of age, when nicotine-treated lambs also had lower ventilation during hypoxia (p < 0.05). The response to hyperoxia was comparable in the two groups at all ages. The ability to terminate laryngeal chemoreflex-induced apnea is attenuated in young lambs continuously exposed to nicotine. This attenuation is present both in normoxia and in hypoxia and is accompanied by reduced effects from sighing on cardiac autoresuscitation.
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PMID:Impaired cardiorespiratory recovery after laryngeal stimulation in nicotine-exposed young lambs. 1250 88

This study examined effects of hyperoxia on thermoregulatory responses. Eight healthy male students (23.5+/-1.8 yrs) were involved in this study. They immersed their legs in a hot water bath (42 degrees C) for 60 minutes in a climate chamber. The conditions of oxygen concentration of a chamber were set at 21% (control), 25% (25%O(2)), and 30% (30%O(2)). Ambient temperature and relative humidity was maintained at 25 degrees C and 50% in every condition, respectively. Measurements included rectal temperature (Tre), skin temperature at 7 sites, laser Doppler flowmeter (LDF) on the back and forearm as an index of skin blood flow, heart rate, local sweat rate (Msw) on the back and forearm, and total body weight loss (BWL). Increases of Tre at 25%O(2) and 30%O(2) tended to be lower during the immersion than in the control. Mean skin temperature (Tsk) of the control increased gradually after the onset of sweating, while the Tsks at 25%O(2) and 30%O(2) maintained a constant level during sweating. LDFs on the forearm at 25%O(2) and 30%O(2) showed lower increases compared with the control. No significant differences in Msw on the back and the forearm and BWL were seen among the conditions. These results suggested that hyperoxia could not affect sweating responses but elicit an inhibitory effect on thermoregulatory skin blood flow.
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PMID:Effects of hyperoxia on thermoregulatory responses during feet immersion to hot water in humans. 1293 33

The quantity and quality of the haemoglobin (Hb) of Daphnia magna is related to oxygen partial pressure in the water. Both the dynamics of hypoxia-induced Hb gene transcription, as well as Hb properties in animals incubated long-term at hyperoxia, normoxia and hypoxia, were investigated. Examination of Hb gene (dhb1-dhb3) transcription showed the expression of dhb2 and especially dhb3 to increase markedly approximately one hour after the onset of hypoxia, whereas dhb1 was expressed more or less constitutively. At an incubation close to anoxia, an onset of dhb3 transcription was found already after two minutes. In long-term incubated animals, concentration and oxygen affinity of Hb were lower at higher oxygen partial pressures. With decreasing oxygen availability, the subunit composition of Hb macromolecules changed. The share of the dhb2-encoded subunit, DHbF, increased already during moderate hypoxia. The increase of dhb3 mRNA (encoding DHbC) may be related to a transient increase of DHbC in the first days of hypoxia and/or to an additional coding of dhb3 for DHbD. The rise of DHbD, and particularly DHbA, only at severe hypoxia coincided with the increase of Hb oxygen affinity. The dhb1-encoded subunits DHbB and DHbE showed either a relatively moderate increase or even a decrease in concentration at hypoxia. In small animals with restricted homeostasis capabilities such as Daphnia, adaptation of the protein equipment seems to be a more effective strategy than allosteric modulator control.
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PMID:Differential haemoglobin gene expression in the crustacean Daphnia magna exposed to different oxygen partial pressures. 1297 82

Alveolar epithelial beta-adrenergic receptor (betaAR) activation accelerates active Na+ transport in lung epithelial cells in vitro and speeds alveolar edema resolution in human lung tissue and normal and injured animal lungs. Whether these receptors are essential for alveolar fluid clearance (AFC) or if other mechanisms are sufficient to regulate active transport is unknown. In this study, we report that mice with no beta1- or beta2-adrenergic receptors (beta1AR-/-/beta2AR-/-) have reduced distal lung Na,K-ATPase function and diminished basal and amiloride-sensitive AFC. Total lung water content in these animals was not different from wild-type controls, suggesting that betaAR signaling may not be required for alveolar fluid homeostasis in uninjured lungs. Comparison of isoproterenol-sensitive AFC in mice with beta1- but not beta2-adrenergic receptors to beta1AR-/-/beta2AR-/- mice indicates that the beta2AR mediates the bulk of beta-adrenergic-sensitive alveolar active Na+ transport. To test the necessity of betaAR signaling in acute lung injury, beta1AR-/-/beta2AR-/-, beta1AR+/+/beta2AR-/-, and beta1AR+/+/beta2AR+/+ mice were exposed to 100% oxygen for up to 204 hours. beta1AR-/-/beta2AR-/- and beta1AR+/+/beta2AR-/- mice had more lung water and worse survival from this form of acute lung injury than wild-type controls. Adenoviral-mediated rescue of beta2-adrenergic receptor (beta2AR) function into the alveolar epithelium of beta1AR-/-/beta2AR-/- and beta1AR+/+/beta2AR-/- mice normalized distal lung beta2AR function, alveolar epithelial active Na+ transport, and survival from hyperoxia. These findings indicate that betaAR signaling may not be necessary for basal AFC, and that beta2AR is essential for the adaptive physiological response needed to clear excess fluid from the alveolar airspace of normal and injured lungs.
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PMID:Upregulation of alveolar epithelial active Na+ transport is dependent on beta2-adrenergic receptor signaling. 1501 30

Amphibious crabs, Cardisoma guanhumi, were acclimated to breathing either air or water and exposed to altered levels of oxygen and/or carbon dioxide in the medium. Hypercapnia (22, 36 and 73 torr CO(2)) stimulated a significant hypercapnic ventilatory response (HCVR) in both groups of crabs, with a much greater effect on scaphognathite frequency (Deltaf(SC)=+700%) in air-breathing crabs than water-breathing crabs (Deltaf(SC)=+100%). In contrast, hyperoxia induced significant hypoventilation in both sets of crabs. However, simultaneous hyperoxia and hypercapnia triggered a greater than 10-fold increase in f(SC) in air-breathing crabs but no change in water-breathing crabs. For water-breathing crabs hypoxia simultaneous with hypercapnia triggered the same response as hypoxia alone-bradycardia (-50%), and a significant increase in f(SC) at moderate exposures but not at the more extreme levels. The response of air-breathing crabs to hypoxia concurrent with hypercapnia was proportionally closer to the response to hypercapnia alone than to hypoxia. Thus, C. guanhumi were more sensitive to ambient CO(2) than O(2) when breathing air, characteristic of fully terrestrial species, and more sensitive to ambient O(2) when breathing water, characteristic of fully aquatic species. C. guanhumi possesses both an O(2)- and a CO(2)-based ventilatory drive whether breathing air or water, but the relative importance switches when the respiratory medium is altered.
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PMID:Oxygen and carbon dioxide sensitivity of ventilation in amphibious crabs, Cardisoma guanhumi, breathing air and water. 1516 78

The Magadi tilapia (Alcolapia grahami, formerly Oreochromis alcalicus grahami) is a remarkable example of teleost life in an extreme environment. Typical conditions include water pH=10, titration alkalinity>300 mM, osmolality=525 mOsm, temperatures ranging from 23 degrees to 42 degrees C, and O(2) levels fluctuating diurnally between extreme hyperoxia and anoxia. A number of relatively small tilapia populations are present in various thermal spring lagoons around the margin of the lake separated by kilometers of solid trona crust (floating Na(2)CO(3)) underlain by anoxic water. Despite the apparent isolation of different populations, annual floods may provide opportunities for exchange of fish across the surface of the trona and subsequent gene flow. To assess the question of isolation among Lake Magadi populations, we analyzed the variable control region of the mitochondrial DNA (mtDNA) from six lagoons. A total of seven mtDNA haplotypes, including three common haplotypes, were observed in all six populations. Several of the Lake Magadi populations showed haplotype frequencies indicative of differentiation, while others showed very little. However, differentiation among lagoon populations was discordant with their geographical distribution along the shoreline. All populations exhibited the unusual trait of 100% ureotelism but specialized morphological and physiological characteristics were observed among several of the lagoon systems. In addition, distinct differences were observed in the osmolality among the lagoons with levels as high as 1,400-1,700 mOsm kg(-1), with corresponding differences in the natural levels of whole-body urea. These levels of osmotic pressure proved fatal to fish from less alkaline systems but remarkably were also fatal to the fish that inhabited lagoons with this water chemistry. Upon more detailed inspection, specific adaptations to differential conditions in the lagoon habitat were identified that allowed survival of these cichlids. Additional evidence against potential for gene flow among lagoons despite the sharing of common mtDNA haplotypes was that the osmolality of floodwaters following a heavy rain showed lethal levels exceeding 1,700 mOsm kg(-1). In isolation, different mtDNA haplotypes would be predicted to go to fixation in different populations due to rapid generation times and the small effective population sizes in a number of lagoons. We propose a model of balancing selection to maintain common mtDNA sequences through a common selection pressure among lagoons that is based on microhabitats utilized by the tilapia.
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PMID:Discordance between genetic structure and morphological, ecological, and physiological adaptation in Lake Magadi tilapia. 1544 26

This study examined the effect of acute hypoxic and hypercapnic cardiorespiratory stimuli, superimposed on existing cardiorespiratory disturbances in tambaqui. In their natural habitat, these fish often encounter periods of hypoxic hypercapnia that can be acutely exacerbated by water turnover. Tambaqui were exposed to periods of normoxia, hypoxia, hyperoxia and hypercapnia during which, externally oriented O2 and CO2 chemoreceptors were further stimulated, by administration into the inspired water of sodium cyanide and CO2-equilibrated water, respectively. Hyperoxic water increased the sensitivity of the NaCN-evoked increase in breathing frequency (f(R)) and decrease in heart rate. Hypoxia and hypercapnia attenuated the increase in f(R) but, aside from blood pressure, did not influence the magnitude of NaCN-evoked cardiovascular changes. Water PO2 influenced the magnitude of the CO2-evoked cardiorespiratory changes and the sensitivity of CO2-evoked changes in heart rate and blood flow. The results indicate that existing respiratory disturbances modulate cardiorespiratory responses to further respiratory challenges reflecting both changes in chemosensitivity and the capacity for further change.
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PMID:Reciprocal modulation of O2 and CO2 cardiorespiratory chemoreflexes in the tambaqui. 1576 6


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