CO2 and the catecholamine content of the adrenal medulla of the rat

In Wistar rats exposed during one hour to mixtures of oxygen and carbon dioxide producing hypoxia, hypercapnia, hyperoxia and hypocapnia, and so on, adrenaline contents of the suprarenals is reduced by high concentration of carbon dioxide (30%), with or without hypoxia. Noradrenaline contents is increased by carbon dioxide (15 to 30%). Hypercapnia is more potent than hypoxia as a suprarenal stimulus.     

Variations in Alveolar Partial Pressure for Carbon Dioxide and Oxygen Have Additive Not Synergistic Acute Effects on Human Pulmonary Vasoconstriction

The human pulmonary vasculature constricts in response to hypercapnia and hypoxia, with important consequences for homeostasis and adaptation. One function of these responses is to direct blood flow away from poorly-ventilated regions of the lung. In humans it is not known whether the stimuli of hypercapnia and hypoxia constrict the pulmonary blood vessels independently of each other or whether they act synergistically, such that the combination of hypercapnia and hypoxia is more effective than the sum of the responses to each stimulus on its own. We independently controlled the alveolar partial pressures of carbon dioxide (Pa_{co 2}) and oxygen (Pa_{o 2}) to examine their possible interaction on human pulmonary vasoconstriction. Nine volunteers each experienced sixteen possible combinations of four levels of Pa_{co 2} (+6, +1, −4 and −9 mmHg, relative to baseline) with four levels of Pa_{o 2} (175, 100, 75 and 50 mmHg). During each of these sixteen protocols Doppler echocardiography was used to evaluate cardiac output and systolic tricuspid pressure gradient, an index of pulmonary vasoconstriction. The degree of constriction varied linearly with both Pa_{co 2} and the calculated haemoglobin oxygen desaturation (1-So ₂). Mixed effects modelling delivered coefficients defining the interdependence of cardiac output, systolic tricuspid pressure gradient, ventilation, Pa_{co 2} and So ₂. No interaction was observed in the effects on pulmonary vasoconstriction of carbon dioxide and oxygen (p>0.64). Direct effects of the alveolar gases on systolic tricuspid pressure gradient greatly exceeded indirect effects arising from concurrent changes in cardiac output.     

Processing of leaf matter by lake-dwelling shredders at low oxygen concentrations

Organic sediments in freshwaters are regularly subject to low concentrations of oxygen. The ability of detritivores to sustain their feeding in such conditions should therefore be of importance for the decomposition process. In the present study, aquaria were used to determine processing rates of five lake-dwelling shredders at three different oxygen concentrations; normoxic (9 mg O₂ l^–1) and two levels of hypoxia (1 and 2 mg O₂ l^–1). Discs of alder leaves (Alnus glutinosa (L.)) were used as food. Four species of caddisfly larvae (Trichoptera Limnephilidae) and the isopod, Asellus aquaticus (L.) were compared in the experiments. Significant differences in processing rates per g animal biomass were found both at normoxia and 2 mg oxygen l^–1. At l mg O₂ l^–1 none of the invertebrates fed on leaf discs. The caddisfly larvae Halesus radiatus (Curtis), being one of the two most efficient shredders at normoxia, did not feed at 2 mg oxygen l^–1. The other species fed at rates 15–50 of that at normoxia. The least efficient shredder at normoxia, A. aquaticus was similar to two of the trichopterans at 2 mg O₂ l^–1. This study shows that the importance of specific shredder species may shift in case of hypoxia. Species-specific traits regarding oxygen sensitivity may also be influential for distribution patterns of shredder species both within and between lakes.     

Oxygen and carbon dioxide sensitivity of ventilation in amphibious crabs, Cardisoma guanhumi, breathing air and water

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.     

Extension of the Functional Range of Respiratory and Gas Exchange Responses in Repetitive Hypoxia

External respiration and gas exchange were studied in healthy volunteers during a session of intermittent normobaric hypoxia (INH) consisting of three cycles of breathing alternately a hypoxic mixture (10.7% O₂) for 5 min and normal air for 5 min. The ventilatory response increased in the successive cycles of hypoxia and gradually decreased during the normoxic intervals. These changes were accompanied by an increase in carbon dioxide in lung air, which was not eliminated by the increased pulmonary ventilation during the hypoxic intervals. However, the mean oxygen consumption did not change during the INH session because the ventilatory reactivity and breathing depth, as well as the efficiency of oxygen utilization, increased from cycle to cycle.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 3, 2005, pp. 100–107.Original Russian Text Copyright © 2005 by Krivoshchekov, G. Divert, V. Divert.     

Arterial Blood Gas Tensions and pH in Acute Asthma in Childhood

Studies of the arterial blood gas tensions and pH in 21 children during 24 acute attacks of asthma showed that all were hypoxic on admission to hospital, and in 10 there was evidence of carbon dioxide retention. Cyanosis, invariably present when the So₂ was below 85%, and restlessness in patients breathing air were the most reliable indices of the severity of hypoxia. There were no reliable clinical guides to the Pco₂ level. Conventional oxygen therapy in tents (25–40%) did not always relieve hypoxia, and in three cases the administration of oxygen at a concentration of 40% or over failed to produce a normal arterial oxygen tension. Uncontrolled oxygen therapy may aggravate respiratory acidosis, and three of our patients developed carbon dioxide narcosis while breathing oxygen. The necessity for blood gas measurements in the management of severe acute asthma in childhood is emphasized.     

Influence of temperature and ambient oxygen on the swimming energetics of cyprinid larvae and juveniles

Synopsis The relationship between respiration and swimming speed of larvae and juveniles (2–100 mg fresh mass) of Danube bleak, Chalcalburnus chalcoides (Cyprinidae), was measured at 15° and 20° C under hypoxic (50% air saturation), normoxic, and hyperoxic (140% air saturation) conditions. In a flow-tunnel equipped with a flow-through respirometer the animals swam at speeds of up to 8 lengths · s^-1; speeds were sustained for at least two minutes. The mass specific standard, routine, and active respiration rates declined with increasing body mass at both temperatures. Metabolic intensity increased with temperature, but also the critical swimming speed (at which oxygen uptake reached its maximum) was higher at 20° than at 15° C by about 30%. Nevertheless, the oxygen debt incurred by the fish at the highest speeds was about 40%, and the net cost of swimming about 32%, lower at 20° than at 15°C. The standard metabolic rate was more strongly dependent on temperature (Q₁₀ around 2.5) than the maximum active rate (Q₁₀ below 2). Whereas standard and routine respiration rates were well regulated over the pO₂-range investigated (8.5–25.8 kPa), the active rates showed a conformer-like pattern, resulting in factorial scopes for activity between 2 and 4. Under hypoxia, the critical swimming speed was lower than under normoxia by about 1.51 · s^-1, but the net cost of swimming was also lower by about 30%. On the other hand, hyperoxia neither increased the swimming performance nor did it lead to a further increase of the metabolic cost of swimming. The hypoxia experiments suggest that in response to lowered tensions of ambient oxygen maintenance functions of metabolism not directly related to swimming may be temporarily reduced, leading to increased apparent swimming efficiency under these conditions. The responses of the larvae of Danube bleak to low temperature and low ambient oxygen are discussed in terms of the metabolic strategies by which energy-limited animals meet the challenge of environmental deterioration.     

Evidence for a morphological component in acid-base regulation during environmental hypercapnia in the brown bullhead (Ictalurus nebulosus)

Summary Exposure of adult brown bullheads Ictalurus nebulosus (120–450 g) to environmental hypercapnia (2% carbon dioxide in air) and subsequent recovery caused transient changes in whole body net sodium flux (J _net ^Na+ ) and net chloride flux (J _net ^Cl- ) resulting largely from changes in whole body sodium influx (J _in ^Na+ ) and chloride influx (J _in ^Cl- ). Scanning electron microscopy (SEM) revealed that the fractional area of chloride cells (CCs) on the interlamellar regions was reduced by 95% during environmental hypercapnia. During post-hypercapnic recovery, gill filament CC fractional area increased. The changes in J _in ^Cl- during and after environmental hypercapnia were closely associated with the changes in CC fractional area while the changes in J _in ^Na+ did not correspond to the changes in CC fractional area. Transmission electron microscopy (TEM) supported the SEM observations of CC surface area changes and demonstrated that these changes were caused by covering/uncovering by adjacent pavement cells (PVCs). Lamellar and filament PVC microvilli density increased during hypercapnia while there was a subsequent reduction in the post-hypercapnic period. These data suggest that an important mechanism of acid-base regulation during hypercapnic acidosis is modification of the chloride cell-associated Cl^-/HCO ₃ ^- exchange mechanism. We suggest that bullheads vary availability, and thus functional activity, of this transporter via reversible morphological alterations of the gill epithelium. The increase in density of PVC microvilli may be associated with sodium uptake and/or acidic equivalent excretion during acidosis.     

Ventilatory response of the diamondback water snake,Natrix rhombifera to hypoxia, hypercapnia and increased oxygen demand

Summary Simultaneous measurements of ventilatory frequency, tidal volume, O₂ uptake, CO₂ output and cardiac frequency were made in the diamondback water snake,Natrix rhombifera while breathing hypoxic (15% to 5% O₂ in N₂) or hypercarbic (2% to 10% CO₂ and 21% O₂ in N₂) gases. The snakes responded to hypoxia by increasing tidal volume and decreasing ventilatory frequency resulting in little change in ventilation (50% increase at 5% inspired O₂), or O₂ uptake and only a light increase in CO₂ output. Hypercarbia to 4.2% inspired CO₂ resulted in a slight hyperventilation but ventilation was depressed at 6.3% inspired CO₂ and became erratic at higher concentrations. The resting rate of O₂ uptake was maintained throughout hypercapnia. Heart rate increased during hypoxia and decreased during hypercapnia. Cutaneous O₂ uptake increased during extreme hypoxia (5% inspired O₂) and cutaneous CO₂ output increased during hypercapnia, probably due to changes in the body-to-ambient gas gradients (Crawford and Schultetus, 1970). Both pulmonary oxygen uptake and ventilation were dramatically increased immediately following 10–15 min experimental dives. The increased ventilation was achieved primarily through an increased tidal volume.     

Air Breathing and Gill Ventilation Frequencies in Juvenile Tarpon, Megalops atlanticus: Responses to Changes in Dissolved Oxygen, Temperature, Hydrogen Sulfide, and PH

This study quantified the air-breathing frequency (ABf in breaths h^–1) and gill ventilation frequency (Vf in ventilations min^–1) of tarpon Megalops atlanticusas a function of PO₂, temperature, pH, and sulphide concentration. Ten tarpon held at normoxia at 22–33°C without access to atmospheric oxygen survived for eight days, and seven survived for 14 days (at which point the experiment was terminated) suggesting that the species is a facultative, rather than an obligate, air breather. At temperatures of 29°C and below ABf was highest and Vf was lowest at low oxygen partial pressures. Tarpon appear to switch from aquatic respiration to air breathing at PO₂levels of roughly 40 torr. The gills were the primary organ for oxygen uptake in normoxia, and the air-breathing organ the primary mechanism for oxygen uptake in hypoxia. At 33°C, both ABf and Vf were elevated but highly variable, regardless of PO₂. There were no mortalities in tarpon exposed to total H₂S concentrations of 0–232µM (0–150.9µM H₂S); however, high sulfide concentrations resulted in very high ABf and Vf near zero. Vf was reduced when pH was acidic. We conclude that air breathing provides an effective means of coping with the environmental conditions that characterize the eutrophic ponds and sloughs that juvenile tarpon typically inhabit.     

Effects of oxygen fraction in inspired air on force production and electromyogram activity during ergometer rowing

Six male rowers rowed maximally for 2500 m in ergometer tests during normoxia (fractional concentration of oxygen in inspired air, F _IO₂ 0.209), in hyperoxia (F _IO₂ 0.622) and in hypoxia (F _IO₂ 0.158) in a randomized single-blind fashion. Oxygen consumption (V˙O₂), force production of strokes as well as integrated electromyographs (iEMG) and mean power frequency (MPF) from seven muscles were measured in 500-m intervals. The iEMG signals from individual muscles were summed to represent overall electrical activity of these muscles (sum-iEMG). Maximal force of a stroke (F _max) decreased from the 100% pre-exercise maximal value to 67 (SD 12)%, 63 (SD 15)% and 76 (SD 13)% (P<0.05 to normoxia, ANOVA) and impulse to 78 (SD 4)%, 75 (SD 14)% and 84 (SD 7)% (P<0.05) in normoxia, hypoxia and hyperoxia, respectively. A strong correlation between F _max and V˙O₂ was found in normoxia but not in hypoxia and hyperoxia. The mean sum-iEMG tended to be lower (P<0.05) in hypoxia than in normoxia but hyperoxia had no significant effect on it. In general, F _IO₂ did not affect MPF of individual muscles. In conclusion, it was found that force output during ergometer rowing was impaired during hypoxia and improved during hyperoxia when compared with normoxia. Moreover, the changes in force output were only partly accompanied by changes in muscle electrical activity as sum-iEMG was affected by hypoxic but not by hyperoxic gas. The lack of a significant correlation between F _max and V˙O₂ during hypoxia and hyperoxia may suggest a partial uncoupling of these processes and the existence of other limiting factors in addition to V˙O₂. Accepted: 2 June 1997     

Effect of intermittent hypoxia or hyperoxia on lung development in preterm rat neonates during constant oxygen therapy

Impaired lung development is a major negative factor in the survival of preterm neonates. The present study was aimed to investigate the impact of constant oxygen, intermittent hyperoxia, and hypoxia on the lung development in preterm rat neonates. Neonatal rats were exposed to 40% O₂ with or without brief hyperoxia episodes (95% O₂) or brief hypoxia episodes (10% O₂) from day 0 to day 14, or to room air. The body weight, radical alveolar count (RAC), and total antioxidant capacity (TAOC) were significantly lower whereas the lung coefficient and malondialdehyde (MDA) were significantly higher in the hyperoxia and hypoxia groups than the air control and constant oxygen group at day 7, day 14, and day 21 after birth. The lung function indexes were reduced by intermittent hyperoxia and hypoxia. In contrast, the constant oxygen therapy increased the lung function. HIF-1α and VEGF expression were significantly increased by hypoxia and decreased by hyperoxia. The constant oxygen therapy only decreased the HIF-1α expression at day 14 and 21. In summary, the constant oxygen treatment promoted lung function without affecting the antioxidative capacity in preterm rat neonates. While intermittent hyperoxia and hypoxia inhibited lung development, decreased antioxidative capacity, and dysregulated HIF-1α/VEGF signaling in preterm rat neonates.     

Gas exchange and blood gases of Puna teal (Anas versicolor puna) embryos in the Peruvian Andes

Oxygen consumption, air cell gases, hematology, blood gases and pH of Puna teal (Anas versicolor puna) embryos were measured at the altitude at which the eggs were laid (4150 m) in the Peruvian Andes. In contrast to the metabolic depression described by other studies on avian embryos incubated above 3700 m, O₂ consumption of Puna teal embryos was higher than even that of some lowland avian embryos at equivalent body masses. Air cell O₂ tensions dropped from about 80 toor in eggs with small embryos to about 45 toor in eggs containing a 14-g embryo; simultaneously air cell CO₂ tension rose from virtually negligible amounts to around 26 torr. Arterial and venous O₂ tensions (32–38 and 10–12 toor, respectively, in 12- to 14-g embryos) were lower than described previously in similarly-sized lowland wild avian embryos or chicken embryos incubated in shells with restricted gas exchange. The difference between air cell and arterial O₂ tensions dropped significantly during incubation to a minimum of 11 torr, the lowest value recorded in any avian egg. Blood pH (mean 7.49) did not vary significantly during incubation. Hemoglobin concentration and hematocrits rose steadily throughout incubation to 11.5 g · 100 ml^-1 and 39.9%, respectively, in 14-g embryos.Abbreviations PO₂ partial pressure gradient of O₂ - BM body mass - D diffusion coefficient - G gas conductance (cm³·s^-1·torr^-1) - conductance to water vapor - IP internal pipping of embryos - P _ACO₂ partial pressure of carbon dioxide in air cell - P _AO₂ partial pressure of oxygen in air cell - P _aCO₂ partial pressure of carbon dioxide in arterial blood - P _aCO₂ partial pressure of oxygen in arteries - P _H barometric pressure (torr) - PCO₂ partial pressure of carbon dioxide - P _IO₂ partial pressure in ambiant air - PO₂ partial pressure of oxygen - P _VCO₂ venous carbon dioxide partial pressure - P _VO₂ mixed venous oxygen partial pressure - SE standard error - VO ₂ oxygen consumption     

Ventilatory sensitivity to carbon dioxide before and after episodic hypoxia in women treated with testosterone.

We hypothesized that the ventilatory threshold and sensitivity to carbon dioxide in the presence of hypoxia and hyperoxia during wakefulness would be increased following testosterone administration in premenopausal women. Additionally, we hypothesized that the sensitivity to carbon dioxide increases following episodic hypoxia and that this increase is enhanced after testosterone administration. Eleven women completed four modified carbon dioxide rebreathing trials before and after episodic hypoxia. Two rebreathing trials before and after episodic hypoxia were completed with oxygen levels sustained at 150 Torr, the remaining trials were repeated while oxygen was maintained at 50 Torr. The protocol was completed following 8-10 days of treatment with testosterone or placebo skin patches. Resting minute ventilation was greater following treatment with testosterone compared with placebo (testosterone 11.38 +/- 0.43 vs. placebo 10.07 +/- 0.36 l/min; P < 0.01). This increase was accompanied by an increase in the ventilatory sensitivity to carbon dioxide in the presence of sustained hyperoxia (VSco(2)(hyperoxia)) compared with placebo (3.6 +/- 0.5 vs. 2.9 +/- 0.3; P < 0.03). No change in the ventilatory sensitivity to carbon dioxide in the presence of sustained hypoxia (VSco(2 hypoxia)) following treatment with testosterone was observed. However, the VSco(2 hypoxia) was increased after episodic hypoxia. This increase was similar following treatment with placebo or testosterone patches. We conclude that treatment with testosterone leads to increases in the VSco(2)(hyperoxia), indicative of increased central chemoreflex responsiveness. We also conclude that exposure to episodic hypoxia enhances the VSco(2 hypoxia), but that this enhancement is unaffected by treatment with testosterone.     

The Challenges of Living in Hypoxic and Hypercapnic Aquatic Environments

Organisms living in coastal waters, and especially estuaries,have long been known to have behavioral or physiological mechanismsthat enable them toexist in water containing low amounts ofoxygen. However, the respiratory consumption of oxygen thatgenerates hypoxia is also responsible for producing significantamounts of carbon dioxide. An elevation of carbon dioxide pressurein water will cause a significant acidosis in most aquatic organisms.Thus, the combination of low oxygen and elevated carbon dioxidethat occurs in estuaries represents a significant environmentalchallenge to organisms living in this habitat. Organisms maymaintain oxygen uptake in declining oxygen conditions by usinga respiratory pigment and/or by making adjustments in the convectiveflow of water and blood past respiratory surfaces (i.e., increasecardiac output and ventilation rate). Severe hypoxia may resultin an organism switching partially or completely to anaerobicbiochemical pathways to sustain metabolic rate. There is alsoevidence to suggest that organisms lower their metabolism duringhypoxic stress. Elevated water CO₂ (hypercapnia) produces anacidosis in the tissues of organisms that breathe it. This acidosismay be wholly or partially compensated (i.e., mechanisms returnpH to pre-exposure levels), or may be uncompensated. Some studieshave examined the effects on organisms of exposure simultaneouslyto hypoxia and hypercapnia. This article reviews some of thespecific adaptations and responses of organisms to low oxygen,to high carbon dioxide, and to the cooccurrence of low oxygenand high carbon dioxide     

REDUCTION OF CARBON DIOXIDE COUPLED WITH THE OXYHYDROGEN REACTION IN ALGAE

1. Unicellular algae possessing a hydrogenase system (Scenedesmus and other species), and having been adapted by anaerobic incubation to the hydrogen metabolism, reduce oxygen to water according to the equation O₂ + 2H₂ → 2H₂O. 2. The oxyhydrogen reaction proceeds undisturbed only in the presence of carbon dioxide, which simultaneously is reduced according to the equation CO₂ + 2H₂ → H₂O + (CH₂O) = (carbohydrate). 3. The maximum yield of the induced reduction is one-half molecule of carbon dioxide reduced for each molecule of oxygen absorbed. 4. Partial reactions are recognizable in the course of the formation of water and it is with the absorption of the second equivalent of hydrogen that the carbon dioxide reduction appears to be coupled. 5. The velocity of the reaction increases in proportion to the partial pressure of oxygen, but only up to a certain point where any excess of oxygen causes the inactivation of the hydrogenase system. The reaction then ends prematurely. 6. During the oxyhydrogen reaction little or no oxygen is consumed for normal respiratory processes. 7. Small concentrations of cyanide, affecting neither photosynthesis nor photoreduction in the same cells, first inhibit the induced reduction of carbon dioxide and then lead to a complete inactivation of the hydrogenase system. 8. Hydroxylamine, added after adaptation, has either no inhibitory effect at all, or prevents solely the induced reduction of carbon dioxide without inactivating the hydrogenase system. 9. Dinitrophenol prevents the dark reduction of carbon dioxide while the reduction of oxygen continues to the formation of water. 10. Glucose diminishes the absorption of hydrogen, probably in its capacity as a competing hydrogen donor. 11. The induced reduction of carbon dioxide can be described as an oxido-reduction similar to that produced photochemically in the same cells.     

Water chemistry changes in the gill micro-environment of rainbow trout: experimental observations and theory

Summary Soft water of low buffer capacity was drawn from near the branchial surface of rainbow trout (Salmo gairdneri) at 15°C, using opercular catheters, to determine pH changes in water passing over the gills. Latex masks allowed measurement of ventilation volume, and concentrations of carbon dioxide, oxygen, ammonia, and titratable base in expired water were compared to concentrations in inspired water. Water passing over the gills was more basic than inspired water if the inspired water was pH 4–6 (maximum increase: +0.7 pH units near pH 5). Expired water was more acidic than inspired water if the inspired water was pH 6–10 (maximum decrease: –1.7 pH units near pH 9). Ventilation volume (0.37 l·kg^–1·min^–1) and oxygen consumption (1.7 mmol·kg^–1·h^–1) were constant in the pH range 4.6–10.1, but both increased by 1.6–2.4× near pH 4. Carbon dioxide transfer near the gills was about 100 M, ammonia transfer about 15 M, and titratable base added at the gills was about 30 M. A theoretical model using CO₂, titratable base, and ammonia added at the gills, the titration characteristics of the defined soft water medium, and aquatic equilibria for CO₂ and ammonia, adequately explained the experimentally observed changes in pH near trout gills. Our observations and predictive model indicate that any gill contaminant whose toxicity varies with pH may be more or less toxic at the gills than predicted from bulk water chemistry alone.Abbreviations pH _ex expired pH - pH _in inspired pH     

Determination of volatile nematode exudates and their effects on a nematode-trapping fungus

Volatile compounds exuded from axenically grown free-living nematodes were determined with gas chromatographic and mass spectrometric techniques. Carbon dioxide evolved from 5–200 nematodes was determined with an ampoule technique, whereas total ammonia (NH₃ + NH₄ ⁺) and acetic and propionic acids were determined by direct injection of water in which nematodes had been suspended for 1–3 days. CO₂ amounted to about 80 ng nematode^–1 d^–1, total ammonia to 1–5 ng, and acetic and propionic acids to 0.5 and 1.0 pg nematode^–1 d^–1.The effects of these compounds on induction of trap formation in the nematodetrapping fungusArthrobotrys oligospora were tested. CO₂ inhibited trap formation at 5–10% CO₂ in air (v/v), whereas ammonia stimulated trap formation in a certain concentration range. No effects of acetic and propionic acids were noted for the concentrations tested. The combined effects of these volatiles in the aqueous environment are discussed on the basis of stoichiometric considerations.     

Fluxes of gases in an ice related ecosystem in the north-western Weddell Sea

Summary During the European Polarstern Study (EPOS leg 1 and leg 2) measurements of temperature, salinity, inorganic nutrients, chlorophyll-a, oxygen and total inorganic carbon dioxide were performed from October to January 1988–1989 in north-south sections at 47–49 °E in the NW Weddell Sea from approximately 58 °S to 63 °S (Hempel 1989; Hempel et al. 1989). In order to explain parts of the obtained data, a time-dependent ecological model was constructed by Svansson (1991). He found that a moderate mixing with a constant diffusion coefficient from sea surface downwards resulted in good agreement between computed and measured chlorophyll. In this paper we introduce the gas fluxes, mainly oxygen but also carbon dioxide, into the model work. It turns out that air-sea fluxes are necessary to explain the vertical oxygen distribution. The annual development of chlorophyll, phosphate, oxygen and total inorganic carbon dioxide are computed. Hours of day-light, losses and the eddy diffusion coefficient are allowed to vary during the year with the condition that the mean total chlorophyll at 14 selected leg 1 stations was nearly double the magnitude of that of 18 selected leg 2 stations. This yields variations consistent with the observations. Different steady-state solutions after 91 days are also tested to show effects of one selected variation at a time, for example the eddy diffusion coefficient or the loss rate. The oxygen air-sea flux, of about 90 mmol m^–2 day^–1 in the time variable model computation, is compared to estimated fluxes by a gas transfer formula. The formula used gives a flux which is about 5 times smaller than the model flux. Some of the 91 days solutions give results of fluxes which are less than 90 mmol m^–2 day^–1 but still higher than the transfer formula result. Fluxes of total inorganic carbon dioxide in the model computation are always directed from air to sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Pre-and post-branchial blood respiratory status during acute hypercapnia or hypoxia in rainbow trout,Oncorhynchus mykiss

Simultaneous venous (pre-branchial) and arterial (post-branchial) extracorporeal blood circulations were utilized to monitor continuously the rapid and progressive effects of acute environmental hypercapnia (water partial pressure of CO₂ 4.8±0.2 torr) or hypoxia (water partial pressure of O₂ 25±2 torr) on oxygen and carbon dioxide tensions and pH in the blood of rainbow trout (Oncorhynchus mykiss). During hypercapnia, the CO₂ tension in the arterial blood increased from 1.7±0.1 to 6.2±0.2 torr within 20 min and this was associated with a decrease of arterial extracellular pH from 7.95±0.03 to 7.38±0.03; the acid-base status of the mixed venous blood changed in a similar fashion. The decrease in blood pH in vivo was greater than in blood equilibrated in vitro with a similar CO₂ tension indicating a significant metabolic component to the acidosis in vivo. Under normocapnic conditions, venous blood CO₂ tension was slightly higher than arterial blood CO₂ tension difference was abolished or reversed during the initial 25 min of hypercapnia indicating that CO₂ was absorbed from the water during this period. Arterial O₂ tension remained constant during hypercapnia; however, venous blood O₂ tension decreased significantly (from 22.0±2.6 to 9.0±1.0 torr) during the initial 10 min. Hypercapnia elicited the release of catecholamines (adrenaline and noradrenaline) into the blood. The adrenaline concentration increased from 6±3 to 418±141 nmol · l^-1 within 25 min; noradrenaline concentration increased from 3±0.5 to 50±21 nmol · l^-1 within 15 min. During hypoxia arterial blood O₂ tension declined progressively from 108.4±9.9 to 12.8±1.7 torr within 30 min. Venous blood O₂ tension initially was stable but then decreased abruptly as catecholamines were released into the circulation. The release of catecholamines occurred concomitantly with a sudden metabolic acidosis in both blood compartments and a rise in CO₂ tension in the mixed venous blood only.Abbreviations CCO₂ plasmatotal carbondioxide - CtO₂ blood oxygen content - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - PaO₂ arterial bloodPO₂ - PaCO₂ arterial bloodPCO₂ - PvCO₂ venous bloodPCO₂ - PwO₂ waterPO₂ - PwCO₂ waterPCO₂ - Hb haemoglobin - SHbO₂ haemoglobin oxygen saturation - HPLC high-performance liquid chromatography - rbc red blood cell(s) - Hct haematocrit