共查询到20条相似文献,搜索用时 31 毫秒
1.
Cardiopulmonary bypass (CPB) procedures require a blood-gas exchanger (oxygenator) to temporarily replace the respiratory function of the lungs. In the past the majority of CPB procedures have been carried out with bubble oxygenators which effect gas exchange by dispersion of bubbles into the blood. Membrane oxygenators, on the other hand, utilize a hydrophobic gas permeable membrane between the blood and gas phases.Bubble oxygenators are being superseded by membrane types for CPB due to improvements in membrane technology and mass transfer efficiency. These advances are reviewed in this paper and are illustrated by reference to the gas exchange and operating characteristics of a number of clinical oxygenators designed for adult CPB.Membrane oxygenatorsare also being used for long-term support in the treatment of acute respiratory failure. Operated in a partial bypass circuit, the oxygenator may have to function for several days or weeks. In one particular treatment method, the rate of spontaneous breathing is controlled by the partial or total removal of the metabolic CO 2 production by the membrane oxygenator. For this method, known as extracorporeal CO 2 removal (ECCO 2R), the oxygenator must be optimized for CO 2 transfer at low blood flow rates. The suitability of clinical oxygenators for ECCO 2R is discussed in terms of gas exchange and functionality over a prolonged operation. 相似文献
2.
Gas transfer performance is presented for one form of the Oxford membrane lung in which vortex mixing is induced in blood flow across a dimpled polypropylene membrane. Dimensional analysis has been used to define the parameters characterizing mass transfer in the device, and of three fluid mechanical parameters: Reynolds number based on peak pulsation velocity, Strouhal number, and ratio of mean to oscillatory flows, only the first has been found to affect mass transfer significantly in the ranges studied. For oxygenation, rated flows in excess of 5 l min −1 m −2 are measured. A new definition is presented for a rated flow for extracorporeal CO 2 removal and values in excess of 1.2 l min −1 m −2 are obtained. 相似文献
3.
Many aquatic algae induce a CO 2-concentrating mechanism (CCM) associated with active inorganic carbon transport to maintain high photosynthetic affinity using dissolved inorganic carbon even in low-CO 2 (LC) conditions. In the green alga Chlamydomonas reinhardtii, a Ca 2+-binding protein CAS was identified as a novel factor regulating the expression of CCM-related proteins including bicarbonate transporters. Although previous studies revealed that CAS associates with the thylakoid membrane and changes its localization in response to CO 2 and light availability, its detailed localization in the chloroplast has not been examined in vivo. In this study, high-resolution fluorescence images of CAS fused with a Chlamydomonas-adapted fluorescence protein, Clover, were obtained by using a sensitive hybrid detector and an image deconvolution method. In high-CO 2 (5% v/ v) conditions, the fluorescence signals of Clover displayed a mesh-like structure in the chloroplast and part of the signals discontinuously overlapped with chlorophyll autofluorescence. The fluorescence signals gathered inside the pyrenoid as a distinct wheel-like structure at 2 h after transfer to LC-light condition, and then localized to the center of the pyrenoid at 12 h. These results suggest that CAS could move in the chloroplast along the thylakoid membrane in response to lowering CO 2 and gather inside the pyrenoid during the operation of the CCM. 相似文献
4.
Microalgae perform oxygenic photosynthesis and are capable of taking up a large amount of CO 2, using an inducible CO 2 concentrating mechanism (CCM), and fixing CO 2 into higher compounds. These characteristics make the microalgae potentially useful for removal and utilization of CO 2 emitted from industrial plants and, generally, the usage of photosynthetic microorganisms has increased and significantly
improved as a solution for CO 2 emissions. In this light and based on previous research using Anabaena cylindrica IAM M1 and Spirulina platensis IAM M 135, enhancement was sought for CO 2 fixation and biomass production by Chlorella vulgaris Buitenzorg by increasing the photon flux density concurrent with increases in culture biomass during the cellular growth
phase and was compared to cultures of Chlorella grown at optimal constant illumination, with all cultures grown using Bennick basal medium, 29°C, and a flow of 1.0 atm.
10% CO 2 enriched air delivered to three in serial photobioreactors of 0.200 dm 3 capacity each. The results showed that increasing illumination during culture increased biomass production of Chlorella by ∼60% as well as increased CO 2 fixation ability by ∼7.0%. It was also demonstrated that the non-competitive inhibition of [HCO 3
−] as a carbon source significantly affected the cultivation in both the increasing and constant photon flux density regimes. 相似文献
5.
Productivity in a CHO perfusion culture reactor was maximized when pCO 2 was maintained in the range of 30–76 mm Hg. Higher levels of pCO 2 (> 150 mm Hg) resulted in CHO cell growth inhibition and dramatic reduction in productivity. We measured the oxygen utilization and CO 2 production rates for CHO cells in perfusion culture at 5.55×10 -17 mol cell -1 sec -1 and 5.36×10 -17 mol cell -1 sec -1 respectively. A simple method to directly measure the mass transfer coefficients for oxygen and carbon dioxide was also developed. For a 500 L bioreactor using pure oxygen sparge at 0.002 VVM from a microporous frit sparger, the overall apparent transfer rates (k La+k AA) for oxygen and carbon dioxide were 0.07264 min -1 and 0.002962 min -1 respectively. Thus, while a very low flow rate of pure oxygen microbubbles would be adequate to meet oxygen supply requirements for up to 2.1×10 7 cells/mL, the low CO 2 removal efficiency would limit culture density to only 2.4×10 6 cells/mL. An additional model was developed to predict the effect of bubble size on oxygen and CO 2 transfer rates. If pure oxygen is used in both the headspace and sparge, then the sparging rate can be minimized by the use of bubbles in the size range of 2–3 mm. For bubbles in this size range, the ratio of oxygen supply to carbon dioxide removal rates is matched to the ratio of metabolic oxygen utilization and carbon dioxide generation rates. Using this strategy in the 500 L reactor, we predict that dissolved oxygen and CO 2 levels can be maintained in the range to support maximum productivity (40% DO, 76 mm Hg pCO 2) for a culture at 10 7 cells/mL, and with a minimum sparge rate of 0.006 vessel volumes per minute.A = volumetric agitated gas-liquid interfacial area at the top of the liquid, 1/mB = cell broth bleeding rate from the vessel, L/minCER = carbon dioxide evolution rate in the bioreactor, mol/min[CO 2] = dissolved CO 2 concentration in liquid, M[CO 2] * = CO 2 concentration in equilibrium with sparger gas, M[CO 2] ** = CO 2 concentration in equilibrium with headspace gas, MCO 2(1) = dissolved carbon dioxide molecule in water[C T] = total carbonic species concentration in bioreactor medium, M[C T] F = total carbonic species concentration in feed medium, MD = bioreactor diameter, mD I = impeller diameter, mD b = the initial delivered bubble diameter, mF = fresh medium feeding rate, L/minH L = liquid height in the vessel, mk A = carbon dioxide transfer coefficient at liquid surface, m/mink
infA
supO
= oxygen transfer coefficient at liquid surface, m/minNomenclature 相似文献
6.
Two-tier vessels, developed for culturing of microalgae and cyanobacteria at high cell density on a shaken platform, were assembled from a flat lower chamber to be filled with a CO 2 buffer and an upper flat sterile chamber for the culture that was separated from the lower chamber by a porous polypropylene membrane. Diffusive gas exchange with the atmosphere was controlled by the O 2 outlet channel. Referred to surface area, rates of CO 2 transfer to a shaken weakly alkaline buffer solution across the membrane were higher than those reached on the conventional pathway through the free upper liquid surface. Membrane-mediated CO 2 supply enabled rapid growth of Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 up to ultrahigh cell density. The biomass (dry weight) concentration of Synechococcus cultures reached more than 30 g L ?1 on a buffered medium with adequate concentrations of mineral nutrients. An increase of 15 to 20 g L ?1 was observed during repeated two-day cycles. Separate pathways for CO 2 supply and oxygen outlet prevented significant loss of CO 2. Convective gas flow through the oxygen outlet channel enabled the estimation of the O 2 generation rate. The permeability of the channel for diffusive O 2/N 2 exchange limited the O 2 concentration to a moderate value. It is concluded that shaken flat cultures using CO 2 supply through a porous hydrophobic membrane and diffusive release of O 2 through a separate pathway are promising for research on microalgae and cyanobacteria. 相似文献
7.
Portable meters and simplified gas Chromatographic (GC) techniques were investigated for monitoring volatile hydrocarbon (HC), CO 2, and O 2, concentrations in groundwater, exhaust gases, and soil vapor during in situ remediation using soil vapor extraction (SVE) and air sparging (AS). Results of groundwater samples analyzed in‐house using a headspace technique compared well to split samples analyzed by a certified analytical laboratory (r 2 = 0.94). SVE exhaust gas HC and CO 2 concentrations measured using a GT201 portable HC/O 2 meter and a RA‐411A meter (GasTech), respectively, were highly correlated with in‐house laboratory GC analyses (r 2 = 0.91). O 2 concentrations fell in a small range and meter analyses were not well correlated with laboratory analyses. Results of soil gas monitoring were not as well correlated as those for exhaust gases for HC, CO 2, or O 2, perhaps due to environmental conditions such as changes in relative humidity or the wider range of soil gas values. Overall, the meters were good indicators of vapor contamination, they greatly simplified estimates of total HC mass removal, and they allowed estimates of the biological contribution to contaminant removal during the remediation process. 相似文献
8.
Red blood cell (rbc) carbon dioxide transport was examined in vitro in three teleosts ( Oncorhynchus mykiss, Anguilla anguilla, Scophthalmus maximus) and an elasmobranch ( Scyliorhinus canicula) using a radioisotopic assay that measures the net conversion of plasma HCO 3− to CO 2. The experiments were designed to compare the intrinsic rates of rbc CO 2 excretion and the impact of haemoglobin oxygenation/deoxygenation among the species.Under conditions simulating in vivo levels of plasma HCO 3− and natural haematocrits, the rate of whole blood CO 2 excretion varied between 14.0 μmol ml −1 h −1 ( S. canicula) and 17.6 μmol ml −1 h −1 ( O. mykiss). The rate of CO 2 excretion in separated plasma was significantly greater in the dogfish, S. canicula. The contribution of the rbc to overall whole blood CO 2 excretion was low in the dogfish (46 ± 6%) compared to the teleosts (trout, 71 ± 4%; turbot, 64 ± 5%; eel, 55 ± 3%).To eliminate the naturally occurring differences in haematocrit and plasma [HCO 3−] as inter-specific variables, the rates of whole blood CO 2 excretion were determined in blood that had been resuspended to constant [HCO 3−] (5 mmol −1) and haematocrit (20%) in appropriate teleost and elasmobranch Ringer solutions. Under such normalized conditions, the rate of whole blood CO 2 excretion was significantly higher in the turbot (22.4 ± 1.3 μmol ml −1 h −1) in comparison to the other species (16.4–18.4 μmol ml −1 h −1) and thus revealed a greater intrinsic rate of rbc CO 2 excretion in the turbot.To study the contribution of Bohr protons, the rates of whole blood CO 2 excretion were assessed in blood subjected to rapid oxygenation during the initial phase of the 3 min assay period. Rapid oxygenation significantly enhanced the rate of CO 2 excretion in the teleosts but not in the elasmobranch. The extent of the increase provided by the rapid oxygenation of haemoglobin was a linear function of the extent of the Haldane effect, as quantified in each species from in vitro CO 2 dissociation (combining) curves. Under steady-state conditions, deoxygenated blood exhibited greater rates of CO 2 excretion than oxygenated blood in the teleosts but not in the elasmobranch. As a consequence of the Haldane effect, rbc intracellular pH was increased in the teleosts by deoxygenation but was unaltered in the elasmobranch.The results, by extrapolation, suggest that the rates of CO 2 excretion in vivo are influenced by the magnitude of the Haldane effect and the extent of haemoglobin oxygenation during gill transit in addition to the intrinsic rate at which the rbc converts plasma HCO 3− to CO 2. 相似文献
9.
We have studied the CO 2 permeability of the erythrocyte membrane of the rat using a mass spectrometric method that employs 18 O-labelled CO 2. The method yields, in addition, the intraerythrocytic carbonic anhydrase activity and the membrane HCO 3− permeability. For normal rat erythrocytes, we find at 37 °C a CO 2 permeability of 0.078 ± 0.015 cm/s, an intracellular carbonic anhydrase activity of 64,100, and a bicarbonate permeability of 2.1 × 10 −3 cm/s. We studied whether the rat erythrocyte membrane possesses protein CO 2 channels similar to the human red cell membrane by applying the potential CO 2 channel inhibitors pCMBS, Dibac, phloretin, and DIDS. Phloretin and DIDS were able to reduce the CO 2 permeability by up to 50%. Since these effects cannot be attributed to the lipid part of the membrane, we conclude that the rat erythrocyte membrane is equipped with protein CO 2 channels that are responsible for at least 50% of its CO 2 permeability. 相似文献
10.
When cells of Anacystis nidulans strain R2 grown under high CO 2 conditions (3%) were transferred to low CO 2 conditions (0.05%), their ability to accumulate inorganic carbon (C i) increased up to 8 times. Cytoplasmic membranes (plasmalemma) isolated at various stages of low CO 2 adaptation were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There was a marked increase of a 42-kilodalton polypeptide in the cytoplasmic membrane during adaptation; a linear relationship existed between the amount of this polypeptide and the C i-accumulating capability of the cells. No significant changes were observed during this process in the amount of other polypeptides in the cytoplasmic membranes or in the polypeptide profiles of the thylakoid membranes, cell walls, and soluble fractions. Spectinomycin, an inhibitor of protein biosynthesis, inhibited both the increase of the 42-kilodalton polypeptide and the induction of high C i-accumulating capability. The incorporation of [ 35S]sulfate into membrane proteins was greatly reduced during low CO 2 adaptation. Radioautograms of the 35S-labeled membrane proteins revealed that synthesis of the 42-kilodalton polypeptide in the cytoplasmic membrane was specifically activated during the adaptation, while that of most other proteins was greatly suppressed. These results suggested that the 42-kilodalton polypeptide in the cytoplasmic membrane is involved in the active C i transport by A. nidulans strain R2 and its synthesis under low CO 2 conditions leads to high C i-transporting activity. 相似文献
11.
An understanding of detailed kinetic of CO 2 removal by plants can lead to an effective design of the phytoremediation process for anthropogenic CO 2 reduction. This study examines the CO 2 removal rates of five wetland plants ( Cyperus alternifolius, Dracaena fragrans, Iris ensata, Iris setosa and Thalia dealbata) by using saturation reaction and first-order reaction kinetic equations. It was determined that the elevation of CO 2 levels stimulated the plant-CO 2 uptake rate. The maximum CO 2 removal rates ( k) of plants were found to range between 0.76 and 1.21 g m ?2 h ?1. The magnitude of first-order kinetic coefficient of plants ( k′) had a close relationship with CO 2 level at half-velocity ( K). For consistency, the same kinetics were applied to the continuous flow experiment. A saturation kinetic approach was well suited to estimate the removal rate of CO 2 in continuous flow system, while a first-order kinetic approach was limited to inflow CO 2 levels below 500 ppm. 相似文献
12.
We have studied the effect of ethoxzolamide, a specific carbonic anhydrase inhibitor, on the velocity of thrombin-stimulated platelet aggregation. After preincubation of platelet rich plasma with 10 ?6 M ethoxzolamide the velocity of platelet aggregation was reduced by about 40%. Between 10 ?11 M and 10 ?10M ethoxzolamide was necessary to achieve a half-maximal diminution of the aggregation velocity. An identical maximal reduction of the velocity of aggregation as with ethoxzolamide could be achieved by a nearly complete removal of CO 2 from the platelet rich plasma. These results suggest that the intracellular CO 2 hydration-dehydration reaction is involved in the activation of human platelets by thrombin. It is possible that the cytosolic carbonic anhydrase of platelets provides a rapid source of the protons that are transferred across the plasma membrane during the activation process. 相似文献
13.
Like humans, the heart rate (HR) of anesthetized rats immersed in CO 2-water is lower than that when immersed in tap water at the same temperature. To investigate the afferent signal pathway in
the mechanism of HR reduction, Wistar rats were anesthetized with urethane and then the spinal cord was transected between
T 4 and T 5. The animals were immersed up to the axilla in a bathtub of tap-water (CO 2 contents: 10–20 mg·l −1) or of CO 2-water (965–1,400 mg·l −1) at 35°C while recording HR, arterial blood pressure, and arterial blood gas parameters ( PaCO 2, PaO 2, pH). Arterial blood gas parameters did not change during immersion, irrespective of CO 2 concentration of the bath water, whereas the HR was reduced in the CO 2-water bath. The inhalation of CO 2-mixed gas (5 % CO 2, 20 % O 2, 75 % N 2) resulted in increased levels of blood gases and an increased HR during immersion in all types of water tested. The HR reduction
observed in sham transected control animals immersed in CO 2-water disappeared after subsequent spinal cord transection. These results show that the dominant afferent signal pathway
to the brain, which is involved in inducing the reduced HR during immersion in CO 2-water, is located in the neuronal route and not in the bloodstream. 相似文献
14.
Summary Carbon dioxide excreted across fish gills is hydrated catalytically to form HCO
3
–
and H + ions in water near the gill surface. We tested the possibility that CO 2 excretion is functionally linked to ammonia excretion through chemical reactions in the gill-water boundary layer. A bloodperfused trout head preparation was utilized in which the convective and diffusive components of branchial gas transfer were controlled. Pre-incubation of blood perfusate with the carbonic anhydrase inhibitor, acetazolamide, reduced both carbon dioxide and ammonia excretion in the blood-perfused preparation. Increasing the buffering capacity of inspired ventilatory water significantly reduced ammonia excretion, but carbon dioxide excretion was unaffected. Each of these experimental treatments significantly reduced the acidification of ventilatory water flowing over the gills. It is proposed that the catalysed conversion of excreted CO 2 to form HCO
3
–
and H + ions provides a continual supply of H + ions need for the removal of NH 3 as NH
4
+
. We suggest, therefore, that acidification of boundary layer water by CO 2 enhances blood-to-water NH 3 diffusion gradients and facilitates ammonia excretion. 相似文献
15.
14CO 2 was applied repeatedly at 3- to 6-h intervals to Kalanchoë daigremontiana leaves during continuous light of differing irradiances. The circadian rhythm in net CO 2 uptake in gasexchange measurements and its disappearance at high irradiances was confirmed by oscillating rates of 14CO 2 incorporation. At 10–30 W m -2 a markedly circadian oscillation in the 14CO 2-uptake rate was measured; with increasing energy fluence rate the oscillation levelled off at a constant high uptake rate. The labelling patterns obtained during the 10 min of 14CO 2 fixation indicated that the rhythm of CO 2 exchange is the consequence of a rhythmic behaviour in the C 4 pathway of CO 2 fixation. During the mininum of 14CO 2 uptake no C 4 products were labelled; however, substantial amounts of label were transferred to C 4 products during the peaks of 14CO 2 uptake. Metabolism of C 3 and C 4 products was also studied in pulsechase experiments at different points of the circadian cycle. In bright light (100 W m -2), when the 14CO 2 uptake was constantly high, the transfer of label into C 4 products (malic acid) was high in spite of the fact that the malate pool is known to be reduced to a permanently low level under these conditions. This led us to the conclusion that it is not the capacity of the phosphoenolpyruvatecarboxylase-mediated CO 2 fixation but rather the storage of malic acid in the vacuole that is disturbed under bright-light conditions when the circadian oscillation levelled off.Abbreviations CAM
Crassulacean acid metabolism
- LL
continuous light
- PEP
phosphoenolpyruvate 相似文献
16.
The CO2 mass transfer model associated with growth kinetics of microalgal biofilm in attached cultivation photobioreactor was developed and verified by using the analysis of pH profiles which were in equilibrium with inorganic carbon components concentrations (CO2, H2CO3, HCO3
− and CO3
2−) in medium. Model simulation results showed that the model well presented the biofilm growth process. The overall volumetric mass transfer coefficient of CO2 was more influenced by CO2 concentration in aerated gas but less by gas aeration rate and medium circulation rate. Other bio-kinetic parameters related with the microalgal biofilm such as CO2 diffusion coefficient in biofilm, Monod maximum utilization rate of CO2, lag phase duration of biofilm and half-saturation CO2 concentration in the biofilm were independent on operational conditions. The pH profiles provided a way to monitor the variations of inorganic carbon concentrations of medium and to regulate the cultivation of attached microalgal biofilm by CO2 supplement. 相似文献
17.
Crop residues like corn ( Zea mays L.) stover perform important functions that promote soil health and provide ecosystem services that influence agricultural sustainability and global biogeochemical cycles. We evaluated the effect of corn stover removal from a no-till, corn-soybean ( Glycine max (L.) Merr) rotation on soil greenhouse gas (GHG; CO 2, N 2O, CH 4) fluxes, crop yields, and soil organic carbon (SOC) dynamics. We conducted a 4-year study using replicated field plots managed with two levels of corn stover removal (none; 55 % stover removal) for four complete crop cycles prior to initiation of ground surface gas flux measurements. Corn and soybean yields were not affected by stover removal with yields averaging 7.28 Mg ha ?1 for corn and 2.64 Mg ha ?1 for soybean. Corn stover removal treatment did not affect soil GHG fluxes from the corn phase; however, the treatment did significantly increase (107 %, P?=?0.037) N 2O fluxes during the soybean phase. The plots were a net source of CH 4 (~0.5 kg CH 4-C ha ?1 year ?1 average of all treatments and crops) during the generally wet study duration. Soil organic carbon stocks increased in both treatments during the 4-year study (initiated following 8 years of stover removal), with significantly higher SOC accumulation in the control plots compared to plots with corn stover removal (0–15 cm, P?=?0.048). Non-CO 2 greenhouse gas emissions (945 kg CO 2-eq ha ?1 year ?1) were roughly half of SOC (0–30 cm) gains with corn stover removal (1.841 Mg CO 2-eq ha ?1 year ?1) indicating that no-till practices greatly improve the viability of biennial corn stover harvesting under local soil-climatic conditions. Our results also show that repeated corn stover harvesting may increase N loss (as N 2O) from fields and thereby contribute to GHG production and loss of potential plant nutrients. 相似文献
18.
We have measured the exchange of 18O between CO 2 and H 2O in stirred suspensions of Chlorella vulgaris (UTEX 263) using a membrane inlet to a mass spectrometer. The depletion of 18O from CO 2 in the fluid outside the cells provides a method to study CO 2 and HCO 3− kinetics in suspensions of algae that contain carbonic anhydrase since 18O loss to H 2O is catalyzed inside the cells but not in the external fluid. Low-CO 2 cells of Chlorella vulgaris (grown with air) were added to a solution containing 18O enriched CO 2 and HCO 3− with 2 to 15 millimolar total inorganic carbon. The observed depletion of 18O from CO 2 was biphasic and the resulting 18C content of CO 2 was much less than the 18O content of HCO 3− in the external solution. Analysis of the slopes showed that the Fick's law rate constant for entry of HCO 3− into the cell was experimentally indistinguishable from zero (bicarbonate impermeable) with an upper limit of 3 × 10 −4 s −1 due to our experimental errors. The Fick's law rate constant for entry of CO 2 to the sites of intracellular carbonic anhydrase was large, 0.013 per second, but not as great as calculated for no membrane barrier to CO 2 flux (6 per second). The experimental value may be explained by a nonhomogeneous distribution of carbonic anhydrase in the cell (such as membrane-bound enzyme) or by a membrane barrier to CO 2 entry into the cell or both. The CO 2 hydration activity inside the cells was 160 times the uncatalyzed CO 2 hydration rate. 相似文献
19.
Oxygen inhibition of photosynthesis and CO 2 evolution during photorespiration were compared in high CO 2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO 2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O 2, which appeared to be competitive and similar in magnitude to that in higher C 3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO 2 cells increased while the O 2 effect declined. Photorespiration, measured as the difference between 14CO 2 and 12CO 2 uptake, was much greater and sensitive to O 2 in high CO 2 cells. Some CO 2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O 2. True photosynthesis was not affected by O 2 in either case. The data indicate that the difference between high CO 2 and air-grown algae could be attributed to the magnitude of CO 2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae. 相似文献
20.
Removal of the jejunum, ileum and colon in the rat reduces the amount of 14CO 2 formed after an intravenous injection of 325 pmoles of 1,25-dihydroxy-[26,27- 14C]vitamin D 3, by 65.2 ± 13.2% at 4 hours and 67.1 ± 9.12% at 8 hours. This suggests that the intestine may be one of the sites where side chain oxidation occurs. It is possible that the liver may also be involved in this process as removal of a large portion of the gut may disturb hepatic metabolism secondary to a reduction in portal blood flow. The process is not bacterial inasmuch as “germ free” animals produce at least as much 14CO 2 after the administration of 1,25-dihydroxy-[26,27- 14C]vitamin D 3 as do non-germ free controls. 相似文献
|