ACID‐BASE RELATIONSHIPS WITHIN THE AVIAN EGG

In 5 different types of rat tumors, the pH of the interstitial fluid ranged from 7.193 to 6.948, the CO2 tension from 59 to 84 mm Hg, the dissolved CO2 from 2.0 to 2.6 mM per liter, and the concentration of bicarbonate from 18.6 to 24.3 mM per liter. Compared with the plasma of blood afferent to the tumor, the pH of the tumor interstitial fluid was 0.2 to 0.4 units lower, the pCO2 16 to 39 mm Hg higher, the dissolved CO2 about 1 mM per liter higher, and the concentration of bicarbonate 4 to 6 mM per liter lower. The same differences were observed when the tumor interstitial fluid was compared with the interstitial fluid of the normal subcutaneous area, though the differences were slightly less when the comparison was made with the plasma of the efferent blood of the tumor or with the lymph of the thoracic duct of the host. A change in the acid-base status of the interstitial fluid of the tumor was produced either by an increase of the CO2 concentration in the air inhaled by the host or by ingestion of sodium bicarbonate or ammonium chloride. When a depression of pH was produced in the blood plasma, a depression roughly equal was found in the interstitial fluid of the tumor. As the pH of this fluid is normally quite low, exceptionally low pH values (6.6–6.7) could be induced exclusively in the tumor. The CO2 tension increased in the tumor to levels twice as high as that in plasma or in the other body fluids of the host, and values of more than 200 mm Hg were reached in the interstitial fluid of the tumor. The amount of dissolved CO2 changed proportionally while the concentration of the bicarbonate showed less drastic oscillations. A peculiarity of NaHCO3 was that it acted as an acidifying agent exclusively in the interstitial fluid of the tumor. Profound changes were produced in the milieu of the tumor, though in the other fluids of the host the parameters of the acid-base equilibrium remained at a level that was physiologically safe.

Angus cattle from 2 beef cattle projects on which carbon dioxide production rate (CPR) was measured were used in this study to examine the relationships among BW, DMI, and carbon dioxide traits of beef cattle fed ad libitum on a roughage diet or a grain-based feedlot diet, and to evaluate potential proxies for DMI and feed efficiency. In both projects, the GreenFeed Emission Monitoring system, which provides multiple short-term breath measures of carbon dioxide production, was used as a tool to measure CPR. The data were from 119 Angus heifers over 15 d on a roughage diet and 326 Angus steers over 70 d on a feedlot diet. Mean (±SD) age, BW, and DMI were 372 ± 28 d, 355 ± 37 kg, and 8.1 ± 1.3 kg/d for the heifers, and 554 ± 86 d, 577 ± 69 kg, and 13.3 ± 2.0 kg/d for the steers, respectively. The corresponding mean CPR was 5760 ± 644 g/d for heifers and 8939 ± 1212 g/d for steers. Other traits studied included carbon dioxide yield (CY; CPR/DMI) and intensity (CI; CPR/BW) and 5 forms of residual carbon dioxide production (RCP), which is a measure of actual minus predicted CPR. Feed efficiency traits studied included feed conversion ratio (FCR) and residual feed intake (RFI). The relationship between CPR and DMI, and between CPR and BW was both positive and linear, for the heifers and also for the steers. For the combined heifer and steer datasets, the R2 for the relationship between CPR and BW, and between CPR and DMI was 0.82 and 0.78, respectively. The correlation between CPR and DMI (r = 0.84 for heifers; r = 0.83 for steers) was similar to that between CPR and BW (r = 0.84 for heifers; r = 0.87 for steers). Most of the carbon dioxide traits were significantly (P < 0.05) correlated with one or both feed efficiency traits. One of the RCP traits (RCPMA) was computed by maintaining metabolic BW (M) and average daily gain (A) in the formula for RFI, but substituting the DMI with CPR. The correlation (r = 0.27) between RCPMA and RFI, though significantly different from zero, was not strong enough for its use as proxy for RFI. On the other hand, a strong correlation (r = 0.73) was obtained between the CPR to gain ratio (CGR) and FCR. This indicates that, where DMI is not available, CPR could be used in its place to compute a feed efficiency trait similar to FCR, since the computation of CGR was similar to that for FCR, except that DMI was substituted with CPR in the FCR formula.

I was interested in the paper of Sellers et al. reporting on the ability of heat stable enterotoxin from E. coli allegedly to stimulate duodenal bicarbonate anion secretion (1). However, I believe the main conclusion is not supported by the data because the chosen physiological techniques do not prove that enhanced bicarbonate anion secretion occurred after the duodenum was exposed to the enterotoxin. Enhanced appearance of bicarbonate anion might arise by enhanced bicarbonate ion secretion but the more likely cause is cessation of hydrogen ion secretion, a known effect of STa that is likely to be the only effect of that enterotoxin (2, 3). The chosen physiological technique was in vivo perfusion followed by measurement of bicarbonate appearance in the lumen of the perfused anaesthetised mouse. Samples were taken and the bicarbonate ion concentration assayed indirectly by titration. The technique involves adding an amount of hydrochloric acid to the sample that will consume the bicarbonate that was present. Back titration with sodium hydroxide to the original sample pH, or even beyond it, estimates the amount of titratable buffer that was initially present but that was consumed by the hydrochloric acid by conversion into carbon dioxide. Any difference between the amount of HCl added and NaOH needed for the back titration allows calculation of the total amount of bicarbonate that was present. In order for this to be assayed directly and with even greater accuracy, any bicarbonate in the buffer that was converted into carbon dioxide could be measured as carbon dioxide. This was measured by the authors and there is no doubt that bicarbonate was converted into carbon dioxide, as sensed by the CO2 gas-sensing electrode. This means that the reader can be confident that bicarbonate in solution was accurately measured. However, the claim that titratable bicarbonate secretion was true bicarbonate secretion and not altered hydrogen ion secretion (Materials and Methods, “Measurement of HCO3 secretion in vivo,” paragraph 3, line 13) is a non-sequitur. The conversion of bicarbonate into carbon dioxide and the establishing that carbon dioxide was indeed formed does not by itself rule out changes in luminal bicarbonate concentration arising because of reduced hydrogen ion secretion. The authors perfused isotonic saline through the duodenum and over time, because of the concentration gradient between the lumen and the interstitial fluid or perhaps because of putative cellular bicarbonate secretion, the bicarbonate concentration increased from zero to the values recorded. In other experiments, the inclusion of STa enterotoxin in the luminal perfusate caused the bicarbonate concentration to increase still further. However, it is known that Na /H exchange occurs in the duodenum, where NHE:3 is present. Bicarbonate that enters the duodenum might be expected to react in part with secreted hydrogen ion so that the eventual bicarbonate concentration that is achieved is the result of appearance of bicarbonate anion and its removal by chemical reaction with secreted hydrogen ion. If the amount of secreted hydrogen ion is reduced by STa, a likely occurrence because it does stop luminal acidification, then it is to be expected that the bicarbonate ion concentration will be higher than normal in the perfused duodenum, as the authors probably showed. This is likely to be the explanation for the higher rates of bicarbonate appearance, given the known effects of STa. It is still possible that bicarbonate secretion is enhanced after STa exposure through the mechanism that the authors invoke but this is not something they have shown in their paper. I believe they have shown that STa reduces hydrogen ion secretion into the lumen and this is manifested by higher concentrations of bicarbonate ion. What they have not shown is that STa stimulates duodenal bicarbonate secretion, certainly not by simply verifying that bicarbonate is convertible into carbon dioxide, as their methods section states. This is a conclusion that goes beyond what the data can reasonably support. A further pharmacological argument in favour of hydrogen ion secretion not being involved is that some of experiments were done in the presence of amiloride. With amiloride inhibiting any hydrogen ion secretion, it might safely be concluded that any subsequent action of guanylin and STa might be restricted to enhanced secretion of bicarbonate ion. It is the case that amiloride might inhibit duodenal NHE:3, but evidence suggests that amiloride and its derivatives are only effective in moderate to low sodium ion containing perfusates (4). Amiloride at 1 mM concentration fails to affect the mucosal surface pH in rat proximal jejunum (5) and 100 uM ethyl-iso-propyl-amiloride (EIPA) fails to inhibit water absorption, whilst STa does inhibit water absorption in high sodium ion containing perfusates (6). Only when the sodium ion concentration is low can

The physicochemical features of eggshell, thick albumen, amniotic fluid, and yolk during chicken embryogenesis

Experiments are described which emphasize the importance of avoiding loss of carbon dioxide when estimating the pH or bicarbonate concentration of ruminal fluid. The high pCO2 of ruminal fluid is stressed; this may be 10 times or more as great as that of arterial blood. The relationship between pCO2, pH, and [HCO3-] was examined in terms of the Henderson-Hasselbalch equation over a wide range of pCO2. From this, the pK1' of the carbonic acid system in four ruminal fluids was determined as 6.21-6.28, mean 6.25. The higher pH of saliva-free samples of ruminal fluid withdrawn by suction through a tube passed down the oesophagus, as compared with that of the bulk fluid obtained through a ruminal fistula, is considered to be due to loss of carbon dioxide during collection. A better estimate of intraruminal pH is obtained, even when salivary contamination occurs, if such samples are equilibrated with a sample of the animal's ruminal gas; if this is not practicable, an arbitrary gas mixture of high pCO2, e.g. 50 per cent. carbon dioxide and nitrogen, may be used.

For the design of high oxygen modified atmosphere packages, knowledge and modelling of respiration rates at both low and super‐atmospheric oxygen levels is required. Fresh‐cut butterhead lettuce was stored in glass jars at three different temperatures (1 °C, 5 °C and 9 °C), three carbon dioxide levels (0, 10 and 20 kPa) and eight different levels of oxygen partial pressures (0, 2, 5, 10, 20, 50, 70 and 100 kPa). Oxygen consumption and carbon dioxide production rates were measured. The respiration rates were significantly reduced by low temperatures and elevated carbon dioxide concentrations up to 10 kPa. At carbon dioxide concentrations of 20 kPa the respiration rates were comparable to those at 0 kPa CO2 probably due to an injury response. Oxygen concentrations had to be below 2 kPa to significantly reduce the respiration rates compared to air conditions. Respiration rates were also slightly lower under super‐atmospheric (50, 70 and 100 kPa) oxygen partial pressures than at air conditions. Additionally, a Michaelis–Menten based model to describe the respiration rates as a function of oxygen, carbon dioxide and temperature was constructed. Models that include respiration rates at super‐atmospheric oxygen levels have not previously been described. The inhibitive effects of carbon dioxide and high oxygen concentrations were incorporated by an uncompetitive and a non‐competitive inhibition term respectively. Temperature effects were described using Arrhenius' law. The model gave a good description (R2adj = 0.82) of the oxygen consumption and carbon dioxide production rates over the temperature, oxygen and carbon dioxide range tested. Copyright © 2006 Society of Chemical Industry

Clinical studies have suggested that use of bicarbonate-containing substitution and dialysis fluids during continuous kidney replacement therapy may result in excessive increases in the carbon dioxide concentration of blood; however, the technical parameters governing such changes are unclear. The current work used a mathematical model of acid-base chemistry of blood to predict its composition within and exiting the extracorporeal circuit during continuous veno-venous hemofiltration (CVVH) and continuous veno-venous hemodiafiltration (CVVHDF). Model predictions showed that a total substitution fluid infusion rate of 2 L/h (33% predilution) with a bicarbonate concentration of 32mEq/L during CVVH at a blood flow rate of 200mL/min resulted in only modest increases in plasma bicarbonate concentration by 2.0mEq/L and partial pressure of dissolved carbon dioxide by 4.4mmHg in blood exiting the extracorporeal circuit. The relative increase in bicarbonate concentration (9.7%) was similar to that in partial pressure of dissolved carbon dioxide (8.2%), resulting in no significant change in plasma pH in the blood exiting the CVVH circuit. The changes in plasma acid-base levels were larger with a higher infusion rate of substitution fluid but smaller with a higher blood flow rate or use of substitution fluid with a lower bicarbonate concentration (22mEq/L). Under comparable flow conditions and substitution fluid composition, model predicted changes in acid-base levels during CVVHDF were similar, but smaller, than those during CVVH. The described mathematical model can predict the effect of operating conditions on acid-base balance within and exiting the extracorporeal circuit during continuous kidney replacement therapy.

THE pH of extracellular fluid is determined by the ratio of the plasma concentrations of bicarbonate ion to carbonic acid, as given in the classical Henderson-Hasselbach equation. [See Equation in Source Pdf] The denominator the carbonic acid concentration, [H2CO3], is proportional to the carbon dioxide tension of the blood. The carbon dioxide tension (pCO2) is primarily dependent upon respiratory function, since metabolism (hence carbon dioxide production) is relatively constant. The numerator of the equation—the bicarbonate concentration of extracellular fluid—is determined by the difference between nonvolatile cations and anions. Since there are almost limitless quantities of bicarbonate available to the organism from cell metabolism, [See Equation in Source Pdf] bicarbonate concentration must change whenever nonvolatile cation (largely sodium) is altered in relation to nonvolatile anion (largely chloride). Thus in most states extracellular bicarbonate concentration is dependent upon the ratio of sodium to chloride in extracellular fluid. The quantity of water filtered at the glomeruli and reabsorbed by the renal tubules each day is approximately 15 times the extracellular volume. The quantity of sodium chloride filtered and reabsorbed daily is approximately 15 times that contained in the extracellular space and 150 times that usually ingested and excreted each day. Therefore, the ratio of plasma sodium to chloride in any steady state is determined by the composition of the renal tubular reabsorbate, as Cushny pointed over 30 years ago. In a sense the kidney perfuses the extracellular space with large quantities of tubular reabsorbate. Tubular reasorbate—the net quantity of materials reabsorbed by the tubules. This term is analogous to glomerular filtrate—the quantity of materials filtered by the glomeruli.

The tensions of respiratory gases and pH of the pleural fluid were evaluated for their possible use in differential diagnosis. The oxygen and carbon dioxide tensions were too variable to be of any use; however, pH might be of diagnostic use since pH values less than 7.29 in nonhemorrhagic pleural fluid were usually associated with nonmalignant inflammatory effusions and higher pH values were seen in effusions secondary to either congestive heart failure, cirrhosis, or malignancy.

Loss of carbon dioxide is an important characteristic fragmentation reaction of deprotonated benzoic acid and its derivatives in electrospray ionization mass spectrometry. However, researchers have rarely noticed or believed that the loss of carbon dioxide in multistage mass spectrometry is a "reversible reaction," that is, the fragment anion generated by carbon dioxide loss can capture another carbon dioxide to regenerate its precursor ion. The fragmentation of the [M - H]- ions of dicamba (3,6-dichloro-2-methoxybenzoic acid) and benzoic acid was performed with an electrospray ionization hybrid quadrupole-orbitrap mass spectrometer. The structural confirmation of the precursor ions and their product ions was supported by accurate mass (elemental composition) analysis. Pseudo-MS3 experiments (in-source collision-induced dissociation as MS2 ) and isotope labelling experiments were used to confirm the addition of carbon dioxide to the product ions in MS2 . In the fragmentation of deprotonated dicamba (m/z 219), the relative abundance of the precursor ion does not decrease significantly or even increases as the collision energy increases. When the m/z 145 and 175 product ions were isolated in the mass analyzer, the ions 44 m/z units larger (m/z 189 and 219) were generated spontaneously, indicating the formation of carbon dioxide adduct ions. In the fragmentation of deprotonated [carboxyl-13 C]-benzoic acid (m/z 122), a deprotonated [carboxyl-12 C]-benzoic acid ion (m/z 121) was generated which was derived from 13 CO2 loss and 12 CO2 addition. The isotope labelling experiment further supports the formation of CO2 -attached ions in the fragmentation of deprotonated benzoic acids. Under collisional activation, deprotonated dicamba and benzoic acids easily undergo carbon dioxide loss, but the decarboxylated product anions have an appropriate nucleophilicity to carbon dioxide and they can capture a background carbon dioxide molecule remaining in the vacuum system to regenerate the precursor ions. This study provides a new and deeper understanding of the gas-phase chemistry of deprotonated benzoic acid derivatives in mass spectrometry.

Changes in rhesus monkey amniotic fluid pH, pCO2, and bicarbonate concentration following maternal and fetal hypercarbia and fetal death in utero

Studies of onion root respiration I. Velocity of oxygen consumption in different segments of root at different temperatures as a function of partial pressure of oxygen

Intestinal lactase activity (with its associated cellobiase, 4-methylumbelliferyl-beta-galactosidase and -beta-glucosidase activities) was used as a specific intestinal marker enzyme to study the release of protein and enzymes of intestinal origin in sheep amniotic fluid during gestation. In amniotic fluid, intestinal lactase activity peaked at 66--85 days of gestation and then decreased with gestation. This enzyme activity was very low or absent in allantoic fluid throughout gestation suggesting that there is no important transfer of amniotic fluid lactase towards the allantoic cavity. Maltase and 4-methylumbelliferyl-alpha-glucosidase showed no statistically significant variation with gestation in both amniotic and allantoic fluid whereas alpha-galactosidase and N-acetyl-beta-hexosaminidase which were first higher in allantoic than in amniotic fluid increased in amniotic fluid to reach allantoic fluid levels near term. Such patterns are consistent with the suggestion that the fetal urine is a source of alpha-galactosidase and N-acety-beta-hexosaminidase activities and that sheep urine is first accumulated in the allantoic sac via the urachus up to 86--90 days of gestation and thereafter passes more and more into the amniotic sac.

Unpublished results obtained by J. K. Hardy (1939) indicate that, under conditions in which carbon dioxide was allowed to accumulate in the atmosphere as a result of the activity of apples when enclosed in gas-tight containers in the absence of oxygen, there was no evidence, over a short period, of a fall in the rate of carbon dioxide production with increasing concentrations of carbon dioxide in the atmosphere, and hence in the tissues. Previous results (Kidd & West, I937) had shown that in air the rate of carbon dioxide production of apples during their post-climacteric phase is progressively depressed with rising concentration of carbon dioxide in the atmosphere, and hence in the tissues. If aerobic carbon dioxide production is depressed by the presence of carbon dioxide but anaerobic carbon dioxide production is not depressed, the fact must be of interest in connexion with the intermediate theories of metabolism of the respiratory process. Experiments have been conducted to check Hardy's results by a method in which the fruits were exposed to a relatively constant pressure of carbon dioxide over a longer period. The method used for the estimation of carbon dioxide production by apples in the presence of carbon dioxide i-n air has already been described (Kidd & West, I933). The experiments were carried out at io0C. Three samples of Bramley's Seedling apples were obtained on 29 September I939. In the case of two of these samples (nos. i and 2) the fruit was pre-climacteric, and in the other (no. 3) post-climacteric. The respiratory history of these three samples is shown in Fig. i (top). The first sample (no. i) was exposed, at the outset, to an atmosphere of pure nitrogen, and it can be seen, by comparing the results with those of the second sample (no. 2), which was in air, that transference from air to nitrogen had very little effect on the rate of carbon dioxide production. Both these samples were preclimacteric. At the point marked A the sample in nitrogen was transferred to an atmosphere of 100% carbon dioxide in nitrogen from which all traces of oxygen had been removed. The carbon dioxide caused a slight, though definite, depression in respiratory activity. At B when the sample was returned to nitrogen without carbon dioxide, oxygen still being absent, the respiratory activity rose again slightly. The second sample (no. 2), which was in air at the outset, began to show its climacteric rise after about 7 days. On the ioth day, before the climacteric rise had fully developed, it was transferred to nitrogen at the point C. The respiratory activity in nitrogen remained on the pre-climacteric level. At the point D when it was transferred to i o % carbon

The effect of maternal hyperoxia and hypoxia on Po2 Pco2, and pH in maternal arterial blood and in amniotic fluid was studied in 8 pregnant women in the second trimester. Hyperoxia with about 100% O2 gave an increase in maternal Pao2, to about 500–600 mmHg followed by a significant increase in amniotic fluid Po2. Pronounced hypoxia (10% O2) reduced maternal Pao2 to about 40 mmHg and caused a significant decrease in amniotic fluid Po2. Minor changes in Pco2, and pH of maternal arterial blood and amniotic fluid were seen during hyperoxia and hypoxia.