Effects of hypercapnia on blood-gas and acid-base status in the white sturgeon, Acipenser transmontanus

The effect of environmental hypercapnia on respiratory and acid-base variables was studied in white sturgeon, Acipenser transmontanus. Blood PCO₂, PO₂, pH, hemoglobin concentration, and plasma lactate, glucose, catecholamines and cortisol were measured first under normocapnia (water PCO₂ < 0.5 Torr, 1 Torr = 133.32 Pa), then under hypercapnia (25–35 Torr) and a final return to normocapnia at 19 ± 0.5 °C. Acute (≤ 2h) hypercapnia significantly increased arterial PCO₂ (8-fold increase), ventilation frequency (2-fold increase), plasma HCO₃ ⁻ (2.3-fold) and decreased arterial pH (to 7.15 ± 0.02). After 24 h, norepinephrine, epinephrine and cortisol, were significantly increased, and arterial pH reached its nadir (7.10 ± 0.03). During the 72- and 96-h-periods, arterial PCO₂ (24 ± 4.4 Torr) and ventilatory frequency (105 ± 5 breaths min⁻¹) stabilized, HCO₃ ⁻ reached its apparent maximum (23.6 ± 0.0 mmol⁻¹), glucose decreased by 32%, and pH increased significantly to 7.31 + 0.03. The return to normocapnia completely restored arterial PCO₂ (2.5 ± 0.14 Torr), HCO₃ ⁻ (7.4 ± 0.59 mmol · l⁻¹), ventilation frequency (71 ± 7 breaths · min⁻¹), and pH (7.75 ± 0.04). Overall, hypercapnia produced a respiratory acidosis, hyperventilation, a transient norepinephrine “spike”, and increased plasma catecholamines, cortisol, and arterial PO₂. The respiratory acidosis was only partially compensated (35% pH restoration) 96 h after the onset of hypercapnia and resulted in a significantly decreased blood-O₂ affinity (Bohr effect), as determined by construction of in vitro blood O₂ equilibrium curves at 15 °C and 20 °C. Prolonged exposure to hypercapnia may lead to acid-base disturbances and negatively affect growth of white sturgeon. Accepted: 17 August 1997     

Regulation of glycolysis in the land snail Oreohelix during estivation and artificial hypercapnia

Summary Respiration rates, hemolymph acid-base variables, and metabolite levels were measured in the land snail Oreohelix during a brief period of estivation (4 days) and during exposure of non-estivating snails to elevated levels of ambient CO₂ (34 and 58 mmHg). Respiration rate dropped during entry into estivation reflecting decreased glycolytic flux. Analyses of metabolite levels in foot muscle and digestive gland tissues demonstrated that glycolytic control during early estivation was primarily vested in pyruvate kinase. Relative to control values, the mass action ratio (MAR) of this reaction decreased by a factor of 4 in the foot muscle and by a factor of 2.7 in the digestive gland, reflecting inhibition of this enzyme in both tissues. No other glycolytic reaction appeared to be inhibited. Exposure of non-estivating snails to artificial hypercapnia resulted in extracellular acid-base conditions similar to those seen during estivation and also promoted a reduction in respiration rate. However, the points of glycolytic control were different: artificial hypercapnia resulted in inhibition of phosphofructokinase in foot muscle and hexokinase in digestive gland. Furthermore, elevated ambient CO₂ had no effect on the MAR of the pyruvate kinase reaction in non-estivating snails. These results suggest that the action of extracellular acid-base variables alone cannot fully explain the down-regulation of glycolysis which occurs during estivation in this land snail.Abbreviations ADP adenosine 5'-diphosphate - AEC adenylate energy charge - AMP adenosine 5'-monophosphate - ANOVA analysis of variance - ATP adenosine 5'-triphosphate - CCO₂ total content of carbon dioxide - EDTA ethylenediamine tetraacetic acid (disodium salt) - AG ^o change in molar standard Gibbs energy - IMP inosine 5'-monophosphate - K _a activation constant - K _eq equilibrium constant - K _m Michaelis constant - MAR mass action ratio - P probability - PCA perchloric acid - PCO₂ partial pressure of carbon dioxide - pH _i intracellular pH - P _i inorganic phosphate - r Spearman's coefficient of rank correlation - SD standard deviation     

Cerebral Metabolic Responses to Electroconvulsive Shock and Their Modification by Hypercapnia

Abstract: Brain glucose metabolism was studied in paralyzed, ventilated rats given electroconvulsive shock (ECS) under normocapnic and hypercapnic conditions. Brains were obtained with a freeze-blowing apparatus. Rates of glucose utilization were determined with [2-¹⁴C]glucose and[³H]deoxyglucose as tracers. In normocapnic rats, ECS caused a large increase in the rate of glycolysis to 5–6 μmol/g/min. Brain lactate levels increased three- to fourfold. The stimulation of glucose metabolism was reflected in decreased brain glucose 6-phosphate concentration as early as 2–3 s after ECS. There were significant decreases in brain glucose and glycogen levels at 20 and 30 s after ECS. The decreases in endogenous brain glucose accounted for most of the increases in glucose utilization measured isotopically, implying that influx of glucose from blood into brain did not increase greatly over these time periods. Animals made hypercapnic by respiration with 10% CO₂ for 2 min prior to ECS were different in their metabolic responses to ECS in several ways. The increases in glycolyt-ic rate and lactate content of brain were half of those found in normocapnic rats. Brain glycogen and glucose concentrations did not change significantly in the hypercapnic rats during seizure activity. Thus, hypercapnia lessened the stimulation of glycolysis caused by ECS, but increased net influx of glucose from blood to brain. The mechanisms of these effects of hypercapnia are uncertain, but it is postulated that the effect on glycolytic activity is due to the acidosis and that the effect on glucose transport is due to an increase in capillary surface area.     

一氧化氮对脑血流的调节

一氧化氮是近年来发现的一种重要的血管活性因子,它通过激活平滑肌细胞内水溶性鸟苷酸环化酶,而产生血管舒张作用,在正常生理条件下,ＮＯ不仅对外因管有作用,对脑血管也有作用,但关于它在低氧和高二氧化碳条件下脑血管是否具有调节作用还存在着争议。     

允许性高碳酸血症对大鼠机械通气相关性肺损伤NF-kB 表达的影响

目的：探讨允许性高碳酸血症对大鼠机械通气相关性肺损伤（VILI）时NF-kB 表达的影响。方法：健康雄性Wistar 大鼠30 只,体重220～280 g,采用随机数字表法,将大鼠随机分3 组（n=10)：对照组（C 组）保留自主呼吸、机械通气肺损伤组（V 组）和 VILI+ 高碳酸血症干预治疗组(H 组)行机械通气4 h。采用吸气相高气道压机械通气模式制备机械通气相关性肺损伤模型。H 组通 过调整吸入的CO2浓度来维持动脉血PaCO2分别为80～100 mmHg。于机械通气15 min 时、机械通气1 h、2 h和4 h 时记录 MAP,采集股动脉血样,进行动脉血气分析,记录PaO2;机械通气结束时,测定支气管肺泡灌洗液(BALF)中总蛋白、TNF-琢和巨噬 细胞炎症蛋白-2（MIP-2）的浓度;取肺组织,测定湿干重比（W/D 比）、细胞间粘附分子（ICAM-1）和NF-kb 蛋白的表达水平,并观 察病理学结果,进行肺损伤评分。测定肺组织丙二醛（MDA）含量及过氧化物歧化酶（SOD）活性。结果：与C 组比较,V 组和H 组 肺损伤评分、W/D 比、ICAM-1表达水平、BALF中总蛋白浓度、TNF-alpha和MIP-2 浓度、MDA 含量和肺组织NF-资B 活性升高,PaO2 降低（P<0.05）;与V 组比较,H 组肺损伤评分、W/D 比、ICAM-1表达水平、BALF 中总蛋白浓度、TNF-alpha和MIP-2 浓度和肺组织 NF-kB 表达降低,SOD活性增强,PaO2升高（P<0.05）。结论：允许性高碳酸血症可下调NF-资B的表达,从而抑制炎症反应减轻大 鼠机械通气相关性肺损伤。     

Mechanisms of dietary Cu uptake in freshwater rainbow trout: evidence for Na-assisted Cu transport and a specific metal carrier in the intestine

Copper (Cu) is both a vital nutrient and a potent toxicant. The objective of this study was to analyze the mechanistic nature of intestinal Cu transport in rainbow trout using radiolabeled Cu (⁶⁴Cu) and an in vitro gut sac technique. Reduction of mucosal NaCl levels inhibited Cu transport while increase caused stimulation; Na₂SO₄ had an identical effect, implicating Na⁺ rather than the anion. These responses were unrelated to solvent drag, osmotic pressure or changes in transepithelial potential. The presence of elevated luminal Ag stimulated Cu and Na⁺ uptake. Phenamil caused a partial inhibition of both Cu and Na⁺ uptake while hypercapnia stimulated Na⁺ and Cu transport. Cu uptake was sensitive to luminal pH and inhibited by a tenfold excess of Fe and Zn. These factors had no effect on Na⁺ uptake. On the basis of these results we propose a novel Na⁺-assisted mechanism of Cu uptake wherein the Na⁺ gradient stimulates an increase in the H⁺ concentration of the brushborder creating a suitable microenvironment for the effective transport of Cu via either DMT1 or Ctr1.     

CO2 enhances effects of hypoxia on mortality,development, and gene expression in cowpea bruchid, Callosobruchus maculatus

Modified atmosphere based on lack of O₂ offers a safe, residue-free alternative to chemical fumigants for pest control in stored grains. In this study, we intended to determine whether elevated CO₂ (at a biologically achievable level) has an enhanced suppressive effect over low O₂ atmosphere alone on the cowpea bruchid (Callosobruchus maculatus), a storage pest of cowpea and other legumes. Experiments were performed under two modified atmospheric conditions, (1) 2% O₂ + 18% CO₂ + 80% N₂ and (2) 2% O₂ + 98% N₂. Both hypoxic environments significantly affected the development and survival of all insect developmental stages. Eggs were most vulnerable to hypoxia, particularly at the early stage (4–6 h old), surviving only up to a maximum of 2 days in both treatments. These were followed by adults, pupae and larvae, in order of decreasing susceptibility. The 3rd and 4th instar larvae were most resilient to hypoxia and could survive up to 20 days of low O₂. The presence of 18% CO₂ significantly increased the mortality of adults, the later stage of eggs, as well as 1st and 4th instar larvae caused by hypoxia. However, the surviving insects exhibited faster development, evidenced by their earlier emergence from cowpea seeds compared to those without CO₂. One interesting observation was the frequent, premature opening of the emergence windows in the 4th instar larvae when CO₂ was involved. This phenomenon was not observed at all in insects stressed by low O₂ alone. Differential expression profiling of metabolic genes and proteolytic activity of midgut digestive enzymes suggested that the rate of metabolic activity could contribute in part to the difference in insect development and survival under hypoxia in the presence and absence of CO₂.     

Blood protein concentrations in the first two postnatal weeks associated with early postnatal blood gas derangements among infants born before the 28th week of gestation. The ELGAN Study

Aim

To explore the relationships between blood gas derangements and blood concentrations of inflammation-related proteins shortly after preterm birth.

Design

Observational cohort.

Setting

Fourteen neonatal intensive care units.

Subjects

Seven hundred and forty five infants born before the 28th week of gestation who were classified by their blood gas derangements during the first three postnatal days and by the concentrations of 25 proteins in their blood on days 1, 7, and 14. We classified these newborns by whether or not they had a highest or lowest P_aO₂, PCO₂, and lowest pH in the most extreme quartile, and by whether or not they had a protein concentration in the highest quartile.

Results

Blood gas derangements on two days were much more likely to be accompanied or followed by sustained or recurrent systemic inflammation than a derangement on only one day. This was most evident for acidemia, and slightly less so for hypercapnia.

Conclusions

Our finding that protein concentration patterns indicative of systemic inflammation are associated with several blood gas derangements raises the possibility that organ damage attributed to these derangements might be accompanied by or involve an inflammatory response.