INCREASED CARBON DIOXIDE TENSION

Rainbow trout were infused continuously for 12h with epinephrine in the presence or absence of alpha-and/or beta-adrenergic blockade to characterize the specific adrenergic mechanisms involved in the control of blood acid-base status and oxygen transport capacity. Infusion of epinephrine, alone, produced a transient respiratory acidosis, as indicated by an increase in carbon dioxide tension and a decrease in whole blood pH, yet arterial oxygen tension was elevated. Red blood cell pH increased by approximately 0.2 pH units during epinephrine infusion and this increase as well as the increase in oxygen tension were prevented by pretreatment with propranolol (a beta-adrenergic antagonist). Epinephrine infusion during alpha-adrenergic blockade caused a prolonged elevation of blood carbon dioxide tension and abolished the increases in hematocrit and hemoglobin concentrations observed during epinephrine infusion alone. Infusion of the alpha-adrenergic agonists phenylephrine (an alpha1 agonist) or clonidine (an alpha2 agonist) caused respiratory acidosis (decreased pH, increased CO2 tension) and a reduction in oxygen tension. Infusion of isoprenaline (a non-specific beta agonist) caused delayed increases in carbon dioxide and oxygen tensions. We speculate that the increased carbon dioxide tension observed during epinephrine infusion is a result of beta-adrenoceptor mediated inhibition of red blood cell bicarbonate dehydration and not branchial convective or diffusive adjustments. The effects of epinephrine on blood O2 tension, content and carrying capacity are discussed with reference to the participation of alpha- and beta-adrenergic mechanisms at the gill, spleen and red blood cell.

OXYGEN MODULATES CONTRACTILE RESPONSES TO POTASSIUM AND PROSTAGLANDIN F2α IN HUMAN PIAL ARTERIES

Rhodobacter sphaeroides has the capacity to grow by aerobic and anaerobic respiration and photosynthetically in the light under anaerobic conditions, as well as fermentatively. It can fix atmospheric nitrogen and carbon dioxide. It resembles other gram-negative members of the class Proteobacteria when growing aerobically, but a reduction in oxygen tension induces an intracellular differentiation of the inner membrane, leading to the formation of the intracytoplasmic membrane system (ICM). The ICM houses the integral membrane pigment-protein complexes constituting the photosystem (PS), comprised of the reaction center (RC) and two light-harvesting (LH) complexes. For an early review of ICM biosynthesis, see reference 44. The LH complexes are designated B800-850 (LHII) and B875 (LHI), based on their respective absorption maxima. The ratio of LHI to RC is fixed at approximately 15:1, whereas the ratio of LHII to the LHI-RC unit is variable, changing in a manner inverse to the incident light intensity. These three pigment-protein complexes are the spectral complexes (SC) of the R. sphaeroides PS. Detailed structural information about these complexes in several species of Rhodobacter is emerging (72). The LH complexes capture light energy and direct that energy to the RC, where conversion of the excitation energy takes place and is intrinsically coupled with a cyclic flow of electrons, ultimately to the periplasmically localized cytochrome c2, which serves to rereduce the RC to allow a new cycle of electron flow (for further details, see references 42, 44, and 72). Bacteriochlorophyll (Bchl) absorbs most of the light energy within the SCs and is critical to the assembly and final structure of the SCs (44, 84, 87). The carotenoids (Crt) have a minor role in absorbing light energy (15), but they function to protect the complexes against photo-oxidative damage, dissipate excess radiant energy, and help to maintain the structure and relative abundance of each SC (35, 50, 53). A reduction in oxygen tension is both necessary and sufficient to induce synthesis of the ICM (reviewed in references 42 and 44), which is gratuitously produced under anaerobic dark growth conditions, in the presence of an alternate electron acceptor such as dimethyl sulfoxide (DMSO). Oxygen tension is the major environmental stimulus controlling PS induction, with variations in light intensity determining the cellular level of the ICM and the abundance of the different SCs. PS formation is tightly regulated, with checkpoints at all levels of information flow, from transcriptional through posttranslational. In the following sections, we will describe what we currently know about the regulatory processes controlling the formation and abundance of SCs in R. sphaeroides. We will present a working model for the regulation of PS formation in R. sphaeroides 2.4.1 which is based on the critical role of cellular redox carriers. For clarity, we will, throughout this review, define aerobic growth as that which occurs under highly oxygenic conditions, under which there are no detectable SCs present in wild-type membranes.

1. Sprout growth is inhibited at 10°C by a concentration of 15 per cent of carbon dioxide in the storage atmosphere, decreased by lower concentrations, and stimulated by still lower concentrations. The optimum concentration for growth need not necessarily be the same in all cases; but appears to be about 2–4 per cent, which would give a concentration in the cell sap of some 0.04–0.05 ml carbon dioxide per ml sap. 2. In agreement with reports by other workers, sprout growth was found to be stimulated by reducing the concentration of oxygen in the storage atmosphere to 5 per cent, which would give a concentration of oxygen in the cell sap of about 0.006 ml oxygen per ml sap. 3. A reduced oxygen tension causes augmented growth either by means of an increase in the number of sprouts or in the number of cells in individual sprouts. A raised carbon dioxide tension causes an increase in the number of cells in the sprouts and also marked cell elongation. 4. Over the range 10–25 C the effect of temperature upon respiration and upon the solubility of gases — and hence upon the concentrations in the cell sap of dissolved oxygen and, more particularly, carbon dioxide —could be an important factor contributing to the effect of temperature upon sprout growth. In some cases the increased sprout growth after some time at a higher temperature may be no more than would be expected as a result of the increased carbon dioxide in solution. 5. Discussion of the results in the light of other work suggests several mechanisms through which changes in the carbon dioxide or oxygen concentrations may influence sprout growth. Such suggestions must be very tentative pending more detailed investigation of the systems involved.

Observations on pregnancy at altitude: I. The respiratory gases in maternal arterial and uterine venous blood

1. The pH of a natural water is determined by the temperature, solids in solution and its carbon dioxide tension. 2. A change in the carbon dioxide tension of a water causes a definite and predictable change in pH, provided the carbon dioxide in solution is the only factor modifying the system. The amount of change in pH with a given change in carbon dioxide tension is determined by the water itself as a chemical system. That is, the pH at a definite carbon dioxide tension and temperature and the amount of change with a definite change in carbon dioxide tension are determined by the characteristics of the natural water itself. 3. Aquatic organisms are able to withstand wide ranges in pH. 4. Aquatic animals are affected in their physiological processes and behavior by changes in carbon dioxide and oxygen tensions. Of the two, a change in carbon dioxide tension is the more effective. 5. All aquatic animals can regulate their internal environment to bring them into harmony with their external environment. Th...

Derivation of endoderm lineages from embryonic stem (ES) cells is receiving immense attention owing to the need for alternative therapies for debilitating diseases like lung cancer, COPD, emphysema, as well as type II diabetes. Some recent examples are derivation of hepatic cells, pancreatic islet-like structures, as well as alveolar cells from ES cells, making ES cell research a very exciting field. However, progress in the field of lung tissue engineering and pulmonary regenerative medicine has been fairly slow, mainly because of (1) lung's structural complexity, (2) cellular heterogeneity, and (3) the low turnover rate of its epithelia. In addition, endodermal differentiation efficiency based on current approaches is still low, and new methods to improve efficiency should be considered. Stromal cell-to-cell contacts, extracellular matrix proteins, temperature, and oxygen (O2) levels in the immediate microenvironment can influence stem cell function and differentiation. Specifically, reduced oxygen tension serves as an important physiological and developmental cue for ES cell differentiation. Low oxygen levels (hypoxia) occur in a number of physiological and patho-physiological settings, particularly when rapid tissue growth exceeds blood supply. Embryogenesis occurs in a physiologically "hypoxic" environment (3%-8% O2). Previous studies have shown that lung epithelial branching is significantly enhanced under 3% O2, in comparison to ambient air. Based on these findings, we hypothesized that mimicking the embryonic microenvironment will increase endodermal differentiation yield. At the time of this writing, there have been no published papers highlighting the use of reduced oxygen tension to enhance murine embryonic stem (mES) cell differentiation towards the endoderm. The goal of this project was to derive endoderm cells from mES cells using oxygen tension as a modulatory parameter. ES cell differentiation is accompanied by apoptosis upon LIF withdrawal. In addition, reduced oxygen tension is accompanied by an increase in cell death due to an increase in reactive oxygen species (ROS). Anti-oxidants like beta-mercaptoethanol (BME) and vitamin-E can act as ROS scavengers, and can improve cell survival. This work was based on the hypothesis that reduced oxygen tension and antioxidants enhance mES cell differentiation towards endoderm. mES cell line ES-D3 was cultured under varying oxygen tensions (1%, 3%, 8%, and 21%) in medium containing 10% fetal bovine serum (FBS) with or without BME, as well as 5% FBS with or without BME for 8 days. Our results, specific to ES-D3 cells, show that cell survival was enhanced in medium containing BME under both ambient (21% O2) and reduced oxygen levels (3%, 8%). Endodermal differentiation markers Sox17 and FoxA2, as assessed by quantitative real-time polymerase chain reaction (Q-PCR), showed highest differentiation in medium supplemented with 5% serum and 0.1mM BME under 21% O2 (P < 0.01 as compared to cells differentiated under reduced oxygen tension). Immunofluorescence confirmed presence of epithelial-cell marker pan-cytokeratin, as well as endothelial cell-marker Griffonia simplicifolia lectin I-isolectinB4, in addition to endodermal markers Sox17 and FoxA2. In contrast to cultures at 21% O2, expression ofboth endodermal markers decreased as oxygen tension decreased to 3% and 8%. All cells died under 1% O2. In conclusion, this work shows that anti-oxidants enhance cell survival under both, normoxic and hypoxic (3% O2) conditions. Reduced oxygen tension (1%, 3%, and 8% O2) suppresses endodermal differentiation of ES-D3 cells in serum-supplemented medium. A combination of reduced oxygen tension and anti-oxidants does not enhance endodermal differentiation, as compared to normoxic controls.

Variations in postbranchial oxygen tensions were studied in vivo in the brackish water isopod Saduria entomon collected from the Baltic Sea in 1992. Haemolymph oxygen tensions were highly influenced by activity. Resting isopods showed small and regular variations in haemolymph oxygen tensions, while a sudden burst of activity caused an immediate reduction in oxygen tension. Periods of no ventilation caused anoxic haemolymph in less than 3 to 4 min. Haemolymph oxygen tension responds rapidly, within seconds to minutes, to changes in isopod activity. Oxygen uptake rates calculated from oxygen tension difference, gill area and membrane thickness were compared with measured values. Permeability studies showed that only 30% of the gill area was effective in oxygen transfer. The present study has confirmed earlier measured oxygen uptake rates and reevaluated the role of the gills as respiratory organs. Postbranchial oxygen tension was established as a function of external steady state oxygen tensions and the intrinsic diffusive conductance was estimated.

A number of experiments have been carried out which indicate that a reduction in oxygen tension reduces irradiation injury in mammals (1, 2, 4), plants (3, 7, 8), yeast (6), and in tissue cultures (5). In mammals, reduced irradiation injury has been demonstrated in cases where the circulation has been impaired (1, 4) by strapping the chests of day-old rats (4), in poorly vascularized tumors (9), and in severe anemia (2). The interpretation and evaluation of each of these experiments are complicated by the presence of several variables. For example, in the experiments in which the circulation of a limb or tail was blocked, other essential metabolites, as well as oxygen, failed to reach the cells. Also, carbon dioxide and other products could not be removed from the cells. In the chest-strapping experiments, the degree of anoxia is unknown, and in the anemia experiments, likewise, secondary responses other than anoxia could have taken place. When all the experiments are considered as a group, however, they have one common factor, namely, reduced oxygen tension. In the plant pollen, tissue culture, and yeast experiments, no circulation is involved. Therefore, anaerobiosis must protect either by its effect on metabolism or by blocking certain radiochemical reactions in which oxygen is necessary. In the studies to be reported here, the effect of extreme anoxic anoxia of brief duration on the LD 50 and on the radiation syndrome observed in mammals after total-body roentgen irradiation has been investigated. By using a brief period of anoxia, it was hoped to avoid any variables caused by the secondary reactions due to anoxia alone. It was observed that anoxia gave a high degree of protection from lethal roentgen irradiation and ameliorated the clinical picture. Materials and Methods In these studies, male and female rats (average weight, 170 gm.) of a Wistar strain were used. The rats were maintained on a diet of Rockland rat chow and given water ad libitum. After irradiation, aureomycin, 25 mg. per cent, was added to the drinking water. Growth curves and clinical appearances were noted for each rat for a period of ten days before irradiation and thirty-five days post irradiation. The rats were irradiated one at a time in an air-tight leucite chamber (10 × 10 × 5 cm.). The gas mixtures from commercial cylinders were bubbled through water and entered the chamber through ¼-inch tubing. The gas escaped from the chamber through a 1-foot length of ¼-inch tubing. The effluent gas was checked for its oxygen content with a Beckman oximeter. The gases were flushed through the chamber for approximately ninety seconds before irradiation to bring about their equilibration and to allow the rats to become anoxic. A continuous flow of gases was maintained during irradiation. The anoxic anoxia rats were irradiated in a mixture of 5 per cent oxygen and 95 per cent nitrogen.

Chemolithotrophic nitrifying bacteria are dependent on the presence of oxygen for the oxidation of ammonium via nitrite to nitrate. The success of nitrification in oxygen-limited environments such as waterlogged soils, will largely depend on the oxygen sequestering abilities of both ammonium- and nitrite-oxidizing bacteria. In this paper the oxygen consumption kinetics of Nitrosomonas europaea and Nitrobacter winogradskyi serotype agilis were determined with cells grown in mixed culture in chemostats at different growth rates and oxygen tensions. Reduction of oxygen tension in the culture repressed the oxidation of nitrite before the oxidation of ammonium was affected and hence nitrite accumulated. K m values found were within the range of 1–15 and 22–166 μM O2 for the ammonium- and nitrite-oxidizing cells, respectively, always with the lowest values for the N. europaea cells. Reduction of the oxygen tension in the culture lowered the half saturation constant K m for oxygen of both species. On the other hand, the maximal oxygen consumption rates were reduced at lower oxygen levels especially at 0 kPa. The specific affinity for oxygen indicated by the V max/K m ratio, was higher for cells of N. europaea than for N. winogradskyi under all conditions studied. Possible consequences of the observed differences in specific affinities for oxygen of ammonium-and nitrite-oxidizing bacteria are discussed with respect to the behaviour of these organisms in oxygen-limited environments.

Fruit physiologists have been concerned with carbon dioxide as a product of the respiratory process and as a factor in the environment surrounding the fruit. Measurement of CO, evolution was favored over determinations of oxygen uptake because of the simplicity of the determination, but a number of investigators realized that CO2 may be produced by anaerobic as well as aerobic pathways of metabolism. Therefore, carbon dioxide is not a sufficient index for establishing the nature of the biological oxidation in the material under study. This realization is of particular significance when fruits are subjected to atmospheric conditions that differ materially from those in air. The interest in modified atmospheres was prompted by the desirability of prolonging storage life, and the chief emphasis was on the observation of fruit quality in increased carbon dioxide and reduced oxygen in the storage environment as compared to ordinary air. Few investigators have concentrated on a systematic change in one component while maintaining constancy in the other. Still fewer have determined respiration as a function of CO, tension, since as long as CO2 measurements were employed by conventional techniques it was not feasible to determine the small amount of carbon dioxide added to the atmosphere containing a relatively high concentration of carbon dioxide. Attempts to develop infrared analysis to achieve such determinations proved excessively complicated. Lack of suitable analytical methods had limited the use of oxygen consumption as a measure of respiration in intact tissues, until Pauling, Wood, and Sturdivant (3) took advantage of the fact that oxygen has an unusually high paramagnetic susceptibility while most other gases are only slightly diamagnetic. They devised a simple and sensitive means of measuring this property of gases and built an instrument which would detect very small changes in the partial pressure of oxygen. The paramagnetic principle was used by the A. 0. Beckman Co. to develop a commercial oxygen analyzer. Since their null type instrument was capable of determining changes in oxygen concentration as small as 0.02 %, it seemed suited to the measurement of respiratory activity in atmospheres high in carbon dioxide. This instrument is characterized by excellent sensitivity, freedom from interference, and linearity over the required range. It also has the unique advantages of requiring no specially calibrated gas mixtures for standardization and of being easily adaptable for automatic sampling and recording. Since the gas is not altered by the determination it may be trapped for other analyses. On the other hand, it has the disadvantage, also inherent in most other methods, that the flow rate must be determined precisely. Several years ago the A. 0. Beckman Co. (Process Instrument Div., Beckman Instrument Co., Fullerton, Cal.) agreed to build an instrument designed to automatically sample and record respiratory activity of fruit subjected to gas mixtures high in CO, and containing from one to 25 % 02 Principle of the Oxygen Analyzer. A schematic illustration of an oxygen analyzer is shown in figure 1. This diagram was supplied by the Beckman Go. and depicts a simplified instrument which illustrates the principle of the analyzer. The paramagnetic detector is shown in the left section of the diagram and consists of a dumbbell-shaped test body suspended on a quartz fiber in the non-uniform field of a permanent magnet. The test body is free to rotate on the fiber in response to magnetic and electrostatic forces. The test body itself is paramagnetic and in the absence of a paramagnetic gas tends to orient in the position of maximum magnetic flux. As oxygen is admitted to the unit, the test body tends to rotate out of the position of maximum magnetic flux in response to the gas becoming more paramagnetic. The degree of rotation is proportional to the difference between the volume magnetic susceptibilities of the test body and the gas that it displaces. A mirror attached to the quartz fiber just above the dumbbell-shaped test body reflects a beam of light to the apex of a front silvered prism, which divides and directs the reflected light beam to two photocells in proportion to the angle of deflection of the test body. Thus any deflection from the null position of the test body causes an unbalance of the output of the two photocells which results in movement of the recorder pen. A precision potentiometer. 1 Received revised manuscript Dec. 20, 1961.

This study was designed to evaluate the sensitivity of changes in myocardial carbon dioxide and oxygen tensions as indicators of regional myocardial ischemia and also to determine to what extent these changes can be related to changes in intramyocardial ST segment voltage. Changes in ST segment voltage recorded in unipolar epicardial electrodes proved to be a less-sensitive indicator of underlying myocardial ischemia than were changes in ST segment voltage recorded in unipolar intramyocardial electrodes. In 9 dogs, regional ischemia was produced by placing a variable constrictor on the left circumflex coronary artery; circumflex flow was monitored. Myocardial carbon dioxide and oxygen tensions were measured using a mass spectrometer. Unipolar electrograms were recorded using a multicontact plunge electrode. With progressive degrees of proximal stenosis, ranging from a critical stenosis, which is associated with a decrease in mean flow of less than 15%, to a severe stenosis associated with and 80% decrease, ST voltage increased 21 mv and carbon dioxide tension increased 84 mm Hg, but oxygen tension decreased only 7 mm Hg. The study suggests that increases in intramyocardial ST segment voltage, an index of myocardial ischemia, are associated with parallel increases in myocardial carbon dioxide tension, each providing a more sensitive quantitative correlate of regional myocardial ischemia than do decreases in oxygen tension. The local accumulation of carbon dioxide may be an important pathophysiological mechanism in myocardial ischemia.

The hyperoxic injury of the microcirculation in the central nervous system appears to be specific to the retina in premature mammals. Oxygen tensions in normal adult mammalian retina and brain vary between nearly 0 and 90 mmHg. This study sought to compare the in vitro replication of retinal and brain microvascular pericytes in normal glucose medium and in 1%, 5% and 20% oxygen (equivalent to 15 mmHg, 35 mmHg and 150 mmHg, respectively). A preliminary study, using oxygen microelectrodes, confirmed that the pericellular oxygen tension of pericytes, cultured in medium under air, was within 13 mmHg of the tension of the gas phase above the media. Pericytes were highly enriched by magnetic antibody cell sorting with the anti-pericyte monoclonal antibody (3G5) to 95% to 99% purity, to remove cell contaminants which may have invalidated the mitogenic assay. Mitogenic assays showed that brain pericytes replicated faster than their counterparts from retina (P < 0.0001, averaged for data from all culture conditions using three-way ANOVA). Reduction of oxygen tension from 150 to 15 mmHg led to significantly increased replication of retinal pericytes (P = 0.01), but an insignificant increase for brain pericytes. We have found that pericytes from the brain and retina cultured conventionally in fetal calf serum consume a relatively low amount of oxygen. Decreasing the oxygen tension to 1% (15 to 20 mmHg) increased the replication of retinal pericytes but not brain pericytes in normal glucose concentrations and in fetal calf serum. That retinal pericyte replication is sensitive to variation in oxygen tensions, indicates that the retinal microvascular cells have a unique biological response. This growth sensitivity to oxygen may be important in the pathogenesis of retinopathy of prematurity.

Introduction and purpose. Vascular response to mechanical stimuli, namely transmural pressure (Bayliss effect) and wall shear stress (response to blood flow), play an important role in regulation of vascular tone. The purpose of the work was to study an influence of hypoxia on the vessel radius and blood flow control by response to shear stress. Methodology/approach. Mathematical simulation was used. The model is based on published data of experiments on small cerebral arteries of rats. The main assumptions of the model are: 1) the vessel is a thin wall cylinder; 2) the radius is controlled by two parameters: concentration of free calcium ions in the cytoplasm of the smooth muscle cells and concentration of nitric oxide (NO) in the smooth muscle layer; 3) the rate of NO production by endothelium is proportional to modulus of shear stress on the vessel wall. The apparent blood viscosity is calculated using the solution of the problem of two-layer flow. The numerical experiments were performed in Turbo Pascal. The main results and discussion. The dependence of vessel tone regulation by response to altered shear stress on oxygen tension is caused by dependence of NO synthesis in endothelium and NO consumption on oxygen concentration. As it follows from mathematical simulation, hypoxia reduces the role of mechanogenic regulation, and the increase of the wall sensitivity to NO makes this effect more appreciable. Calculations performed for typical value of cerebral vessel response to shear stress, show that the fall in oxygen tension from 100 to 30 per cent leads to decrease in diameter by 6 %, in blood flow rate by 11 %. The rheological factors prevent flow rate diminution, but their contribution is very small: less than 3 %. The fall in oxygen tension reduces NO production rate by endothelial cells and NO concentration in the vessel wall. At strong hypoxia (reduction in oxygen tension from 100 to 30 % and less) NO concentration in smooth muscle layer drops by more than 15 %. Conclusions. Hypoxia decreases NO-dependent vessel response to altered shear rate. This effect increases with the value of vessel response to shear stress. The rheological factors impede the decrease of this response.

Recent studies suggest that oxygen tension has a great impact on the osteogenic differentiation capacity of mesenchymal cells derived from adipose tissue: reduced oxygen impedes osteogenesis. We have found that expansion of mouse adipose-derived stromal cells (mASCs) in reduced oxygen tension (10%) results in increased cell proliferation along with induction of histone deacetylase (HDAC) activity. In this study, we utilized two HDAC inhibitors (HDACi), sodium butyrate (NaB) and valproic acid (VPA), and studied their effects on mASCs expanded in various oxygen tensions (21%, 10%, and 1% O(2)). Significant growth inhibition was observed with NaB or VPA treatment in each oxygen tension. Osteogenesis was enhanced by treatment with NaB or VPA, particularly in reduced oxygen tensions (10% and 1% O(2)). Conversely, adipogenesis was decreased with treatments of NaB or VPA at all oxygen tensions. Finally, NaB- or VPA-treated, reduced oxygen tension-exposed (1% O(2)) ASCs were grafted into surgically created mouse tibial defects and resulted in significantly increased bone regeneration. In conclusion, HDACi significantly promote the osteogenic differentiation of mASCs exposed to reduced oxygen tension; HDACi may hold promise for future clinical applications of ASCs for skeletal regeneration.