Rate of oxygen consumption during embryonic development of great ramshorn <Emphasis Type="Italic">Planorbarius corneus</Emphasis> (Gastropoda)

Energy metabolism is studied in great ramshorn Planorbarius corneus during embryonic development. It is shown that the rate of oxygen consumption is constantly increasing in the process of embryogenesis. The respiration intensity (rate of the oxygen consumption per unit of the embryo volume) initially increases and then slowly decreases until eclosion. At the early stages of development until the early trochophore stage, the embryo is not growing, and, thus, the change in the rate of oxygen consumption during this period is not associated with the change of the embryo volume. Reduction in the intensity of respiration begins simultaneously with the beginning of the growth of the embryo at the stage of the middle trochophore. Starting from the middle trochophore and until eclosion, an association between oxygen consumption rate and volume of the embryo can be described with an allometric equation with exponential coefficient equal to approximately 0.23.     

Estimation of human fetal-placental unit metabolic rate by application of the Bohr principle

The Bohr Principle via continuous indirect calorimetry was used to estimate human fetal-placental unit metabolic rate in 12 normal women undergoing elective caesarean section under continuous lumbar epidural anaesthesia. Maternal oxygen consumption decreased after umbilical cord clamping and after placental removal. Fetal-placental unit oxygen consumption was 10.7 +/- 1.3 ml/min per kg (mean +/- SEM). Fetal oxygen consumption was 6.8 +/- 1.4 ml/min per kg. Placental oxygen consumption was 37 +/- 12 ml/min per kg. Fetal-placental unit carbon dioxide production was 9.2 +/- 1.2 ml/min per kg. These mean values agree favourably with measurements of uterine and fetal metabolism from other mammalian species. Maternal minute ventilation decreased with removal of the fetal-placental unit, and this decrease was found to be linearly related to the fetal-placental unit carbon dioxide production.     

A reduction in the in situ rates of oxygen and glucose consumption of cells in EMT6/Ro spheroids during growth

The rates of consumption of oxygen and glucose by EMT6/Ro cells in multicellular spheroids were measured at various times during normal growth. In situ spheroid cellular consumption rates were similar to those of exponentially growing single cells up to a spheroid diameter of 150 micron. Further growth resulted in decreases in the rates of both oxygen and glucose consumption which were correlated with the increase in spheroid diameter and cell number. At a diameter of 1300 micron, both rates of cellular consumption had decreased by a factor of 2.5. The rates of consumption per unit of nonnecrotic spheroid volume decreased in a similar manner. Measurements with single cells demonstrated that the rate of oxygen consumption was coupled with glucose concentration, and vice versa. The rates of consumption for cells dissociated from small spheroids indicated that there was some effect of the spheroid environment. As the spheroids grew, however, association in the spheroid structure accounted for a smaller proportion of the total observed reduction in the rates of nutrient consumption. The presence of central necrosis also appeared to have no effect on the rates of consumption of these nutrients. Spheroid-derived cells showed a decrease in cell volume with growth as the cells accumulated in a quiescent state. Measurements with single cells demonstrated that oxygen and glucose consumption were correlated with cell volume and with the development of nonproliferating cells. We conclude that the observed decrease in oxygen and glucose consumption with growth in spheroids is largely due to the progressive accumulation of cells in a quiescent state characterized by an inherently lower cellular rate of nutrient utilization.     

The rate of oxygen consumption during embryogenesis of Lymnaea stagnalis (Gastropoda)

We studied the rate of oxygen consumption by the Lymnaea stagnalis embryos. The rate of oxygen consumption increased consistently during embryogenesis. The volume specific rate of oxygen consumption increased initially from the early cleavage stages until the gastrula stage and then decreased gradually to the eclosion of snails. There are three periods in embryogenesis of L. stagnalis, which differ in the coefficients of allometric dependence between the rate of oxygen consumption and volume of embryos: (1) early embryogenesis, when the increase in the rate of oxygen consumption is not accompanied by the growth of volume of the embryos; (2) larval period (trochophore and veliger stages; exponential coefficient k = 0.514), and (3) postlarval period (exponential coefficient k = 0.206).     

Local oxygen gradients near isolated mitochondria.

The oxygen concentration in tissue can vary on several length scales. The basic scale of variation is determined by capillary spacing. It is this scale that is manifest in the simplest Krogh cylinder model. A second, smaller scale of variation is associated with the consumption of oxygen by mitochondria. This paper gives a theoretical analysis of these smaller-scale oxygen variations near an isolated mitochondrion. To illustrate the effects of shape, we have carried out the calculations for prolate spheroids as well as for spheres. The principal result is that the local drop in oxygen pressure around a consuming mitochondrion is of the order of (gamma/3K) (3V/4 pi)2/3, where gamma is the oxygen consumption rate per unit mitochondrial volume, K is the Krogh oxygen diffusivity of the surrounding tissue, and V is the mitochondrial volume. The theory is applied to skeletal muscle in vivo and to hepatocytes in cell suspension experiments. In both cases, we find that local oxygen variations produced by oxygen consumption are much smaller than the cell-wide variations produced by the collective effect of all the mitochondria. For example, in maximally consuming skeletal muscle, the drop in oxygen pressure around a consuming mitochondrion is only of the order of 0.03 Torr.     

Oxygen supply controls the onset of pristinamycins production by Streptomyces pristinaespiralis in shaking flasks

Antibiotics are secondary metabolites, generally produced during stationary phase of growth under different nutritional and hydrodynamic stresses. However, the exact mechanisms of the induction of antibiotics production are still not clearly established. In a previous study, the induction of pristinamycins production by Streptomyces pristinaespiralis as well as product concentrations were correlated with power dissipation per unit of volume (P/V) in shaking flasks. In this study, detailed kinetics of growth, substrate consumption, oxygen transfer rate and pristinamycins production under varying P/V conditions have been obtained and analyzed. Our results showed that higher P/V resulted in a higher concentration of biomass and promoted an earlier nutrient limitation and ultimately an earlier induction of pristinamycins production. The maximal specific growth rate, specific oxygen consumption rate and specific consumption rate of glutamate increased with P/V while influence was less marked with specific consumption rate of glucose, arginine, ammonium ions and phosphate. When oxygen uptake rate (OUR) was limited by free-surface oxygen transfer, pristinamycins production was not detected despite the occurrence of nitrogen and/or phosphate sources limitation. The threshold value for OUR observed was around 25 mmol L(-1) h(-1). This suggested that a limitation in nitrogen and/or phosphate alone was not sufficient to induce pristinamycins production by S. pristinaespiralis pr11. To induce this production, the oxygen transfer had to be non-limiting.     

The rate of oxygen consumption during embryogenesis of Lymnaea stagnalis (Gastropoda)

We studied the rate of oxygen consumption by the Lymnaea stagnalis embryos. The rate of oxygen consumption increased consistently during embryogenesis. The volume specific rate of oxygen consumption increased initially from the early cleavage stages until the gastrula stage and then decreased gradually to the eclosion of snails. There are three periods in embryogenesis of L. stagnalis, which differ in the coefficients of allometric dependence between the rate of oxygen consumption and volume of embryos: (1) early embryogenesis, when the increase in the rate of oxygen consumption is not accompanied by the growth of volume of the embryos; (2) larval period (trochophore and veliger stages; exponential coefficient k = 0.514), and (3) postlarval period (exponential coefficient k = 0.206).     

Effect of hydromechanical forces on the production of filamentous haemagglutinin and pertussis toxin ofBordetella pertussis

Summary The production ofBordetella pertussis extracytoplasmic filamentous haemagglutinin (FHA) and pertussis toxin (PT) in a bioreactor under stirring conditions was studied in order to investigate the effect of hydromechanical forces on yields of both antigens. It was shown that FHA loses its haemagglutinin activity when the power transmitted by the agitator and the aerator per unit volume increases, whereas PT production is not affected. The loss of FHA activity can be explained by the action of shear forces on the filamentous structure of this antigen.Nomenclature C^* dissolved oxygen saturation concentration - C₁ dissolved oxygen concentration - D impeller diameter - power transmitted by the agitator and the aerator per unit of liquid volume - E_m maximum local energy dissipation rate per unit of liquid volume - K_La volumetric oxygen transfer coefficient - N impeller speed - Pg power input in aerated system - qO₂m maximum specific oxygen consumption rate - R_e Reynold number (D²N /) - VVM volume of air per volume of fermentation broth per minute - Xm maximum of biomass concentration - o Kolmogorov-microscale - fermentation broth viscosity - fermentation broth kinematic viscosity - fermentation broth density - expt experiment     

The effects of the anaesthetic quinaldine on oxygen consumption in an intertidal teleost Blennius pholis (L.)

The effects of the anaesthetic quinaldine on oxygen consumption in an intertidal teleost Blennius pholis (L.) were investigated. Oxygen consumption generally decreases with increasing quinaldine concentration in environmental water. However, at low concentrations, oxygen consumption of smaller specimens is slightly increased. Generally, smaller specimens have their oxygen consumption affected less by a given quinaldine concentration than do larger specimens, as the former appear to be at less depressed stages of anaesthesia. This is thought to be due to smaller B. pholis becoming saturated with quinaldine more rapidly but simultaneously being afforded more rapid removal, because of their greater relative gill area per unit body volume. The reduction of oxygen consumption at high concentrations of quinaldine is great.     

The ejector-loop fermenter: Description and performance of the apparatus

A novel fermentation unit, the ejector-loop fermenter (ELF), consisting of an outer-loop tower fermenter, a centrifugal pump, a plate-heat exchanger, and a gas-liquid ejector, was designed and constructed. Aeration was achieved by continuously recirculating the fermentation medium through two different nozzle devices instead of using the traditional expensive air compressor. By carrying out a whey fermentation with Kluyveromyces fragilis as the test organism, either in the ELF or in conventional stirred fermenter, it was possible to confirm that the high sheat streses and mixing shock occurring in the ejector nozzle and diffuser sections did not affect microbial growth. Within the range of experimental power consumption per unit volume (-0.1-5 kW/m(3)), the oxygen transfer capability of the ELF per unit power input was found to vary from 1 to 2.5 kg O(2) kW(-1)h(-1). Moreover, it is shown that there is suficient room for improvement in the performance of the ELF unit by care fully designing the aeration device. In fact, at constant volumetric oxygen transfer coefficient, the power consumpotion per unit volume in a 4-mm nozzle was found to be about 40% less than that in a 6-mm nozzle.     

ON THE RATE OF OXYGEN CONSUMPTION BY FERTILIZED AND UNFERTILIZED EGGS : V. COMPARISONS AND INTERPRETATION

1. The rate of oxygen consumption by eggs may not merely undergo no change at fertilization, as in the case of the starfish, but it decreases to about half in Chaetopterus and in Cumingia. 2. The absolute rate of oxygen consumption in mm.³ O₂ per hour per 10 mm.³ eggs differs widely in several species of unfertilized eggs. It is very low in the sea urchin, intermediary in Nereis, and high in Chaetopterus and Cumingia. The range for these eggs is approximately 0.4 to 3.1 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C., in the ratio of about 1:8. 3. The absolute rates of oxygen consumption by the same fertilized eggs are much more nearly the same. They lie within the range 1.3 to 2.0 mm.³ O₂ per hour per 10 mm.³ eggs at 21°C., in the ratio of approximately 1:1.5. Within this same range lie the values obtained by a number of investigators using a variety of eggs of invertebrates from several phyla. Amoeba proteus and frog skin also are within this range (see Fig. 2). 4. The changes in rate of oxygen consumption at fertilization by the different species of eggs, differing both in direction and magnitude, appear to be such as to bring the rate, when development is initiated, to about the same rate, which is also the rate of other comparable normally growing cells. 5. The direction and magnitude of the change in rate at fertilization therefore appears in the cases cited to be primarily a function of the absolute rate of oxygen consumption by the unfertilized eggs, which are characterized in their peculiar inhibited condition, among other things, by a wide range of respiratory rates. 6. It is not to be supposed that this range of rates will apply at all universally to eggs, especially to eggs of extremes in proportional content of inert materials, such as large yolky eggs. Fish and amphibian eggs for example respire at a much lower rate per unit volume. The effect on surface: volume ratios attending extremes of cell size might also be expected to shift the absolute rate. 7. The absolute rate of oxygen consumption by the eggs of the alga Fucus vesiculosus is considerably higher than the rates of the animal eggs measured. It is of the same order of magnitude as the rates of several other small-celled algae, which respire at a greater rate per unit volume than most non-motile animal cells. 8. The comparatively high rates of oxygen consumption by the inhibited (unfertilized) eggs of Chaetopterus and Cumingia are not directly associated with nuclear or morphological activity of the cell since they continue at the high rate for hours after cessation of the brief initial nuclear activity, which takes place when the eggs are placed in sea water. 9. It is concluded that the rate of oxygen consumption is not necessarily and probably not generally the limiting factor which causes inhibition of the unfertilized egg. Increase in rate of oxygen consumption is not directly related to the initiation of development, in general, nor even necessarily concomitant. It is not improbable that the low rate of oxygen consumption is an immediate part of the cause of inhibition of the unfertilized sea urchin egg, but this is a special case. 10. This thesis, that the rate of oxygen consumption is not necessarily nor ordinarily the limiting factor in the inhibition of the unfertilized egg, and conversely that increase in the rate of oxygen consumption is not usually the essential feature of fertilization, is quite in agreement with the general relations between the rate of oxygen consumption on the one hand and anesthesia, growth, and development on the other in fertilized eggs and other organisms. 11. This conclusion is opposed to Loeb''s explanation of the essential feature of fertilization, as an increase in oxidation rate or more strictly to generalization of his hypothesis to include eggs other than those of the sea urchins (or of other similar special cases which may be discovered). It extends to fertilization (the initiation of development) his and Wasteney''s well established conclusion that "oxidation is not the independent variable in development." 12. It is suggested that the crux of the problem of fertilization lies in the nature of the inhibition of the unfertilized egg. Certain similarities between this condition, arrived at spontaneously in the case of the egg cell, and the condition of cells in narcosis or anesthesia are pointed out. 13. Although the rate of oxygen consumption by the unfertilized eggs of Chaetopterus and Cumingia cannot be regarded as the limiting factor which causes the inhibition of the eggs, in these and other cases with different absolute rates, it appears highly probable that the rate of oxygen consumption is in some way, at present obscure, tied up with or related to the condition of inhibition. This seems probable especially in view of the sharp change in rate which in most cases immediately attends cessation of the inhibition, but the relationship may be a non-causal one, as in narcosis. 14. It must be borne in mind that oxygen consumption is not necessarily a complete measure of oxidation, and that other measures such as of heat and metabolite production are necessary before the complete amount of oxidation is known. When these are completely worked out, if free energy relations are known, it is probable that more direct and inclusive relations may be found between oxidation, growth, development, and anesthesia. Generalization of Loeb''s hypothesis, using "oxidation" in the broad sense might then turn out to hold, with fertilization fitting into the general scheme, but there is no basis for it at the present time.     

Oxygen transfer kinetics of riboflavin fermentation by Ashbya gossypii in agitated fermentors

Effects of agitation and aeration rates on volumetric oxygen transfer coefficient and oxygen uptake rate of a riboflavin broth containing Ashbya gossypii were investigated in three batch, sparged, and agitated fermentors having the working volumes of 0.42, 0.85, and 2.5 l. The change of oxygen uptake rate with time at 250 rev min⁻¹ stirring and vvm aeration rates was shown. The volumetric oxygen transfer coefficients and maximum oxygen uptake rates obtained have been correlated to mechanical power inputs per unit volume of the fermentation broth and the superficial air velocities.     

Low Mitochondrial Free Radical Production Per Unit O2 Consumption Can Explain the Simultaneous Presence of High Longevity and High Aerobic Metabolic Rate in Birds

Birds are unique since they can combine a high rate of oxygen consumption at rest with a high maximum life span (MLSP). The reasons for this capacity are unknown. A similar situation is present in primates including humans which show MLSPs higher than predicted from their rates of O₂ consumption. In this work rates of oxygen radical production and O₂ consumption by mitochondria were compared between adult male rats (MLSP = 4 years) and adult pigeons (MLSP = 35 years), animals of similar body size. Both the O₂ consumption of the whole animal at rest and the O₂ consumption of brain, lung and liver mitochondria were higher in the pigeon than in the rat. Nevertheless, mitochondrial free radical production was 2-4 times lower in pigeon than in rat tissues. This is possible because pigeon mitochondria show a rate of free radical production per unit O₂ consumed one order of magnitude lower than rat mitochondria: bird mitochondria show a lower free radical leak at the respiratory chain. This result, described here for the first time, can possibly explain the capacity of birds to simultaneously increase maximum longevity and basal metabolic rate. It also suggests that the main factor relating oxidative stress to aging and longevity is not the rate of oxygen consumption but the rate of oxygen radical production. Previous inconsistencies of the rate of living theory of aging can be explained by a free radical theory of aging which focuses on the rate of oxygen radical production and on local damage to targets relevant for aging situated near the places where free radicals are continuously generated.     

The responses of photosynthesis and oxygen consumption to short-term changes in temperature and irradiance in a cyanobacterial mat (Ebro Delta, Spain)

We have evaluated the effects of short-term changes in incident irradiance and temperature on oxygenic photosynthesis and oxygen consumption in a hypersaline cyanobacterial mat from the Ebro Delta, Spain, in which Microcoleus chthonoplastes was the dominant phototrophic organism. The mat was incubated in the laboratory at 15, 20, 25 and 30 degrees C at incident irradiances ranging from 0 to 1,000 micromol photons m(-2) s(-1). Oxygen microsensors were used to measure steady-state oxygen profiles and the rates of gross photosynthesis, which allowed the calculation of areal gross photosynthesis, areal net oxygen production, and oxygen consumption in the aphotic layer of the mat. The lowest surface irradiance that resulted in detectable rates of gross photosynthesis increased with increasing temperature from 50 micromol photons m(-2) s(-1) at 15 degrees C to 500 micromol photons m(-2) s(-1) at 30 degrees C. These threshold irradiances were also apparent from the areal rates of net oxygen production and point to the shift of M. chthonoplastes from anoxygenic to oxygenic photosynthesis and stimulation of sulphide production and oxidation rates at elevated temperatures. The rate of net oxygen production per unit area of mat at maximum irradiance, J0, did not change with temperature, whereas, JZphot, the flux of oxygen across the lower boundary of the euphotic zone increased linearly with temperature. The rate of oxygen consumption per volume of aphotic mat increased with temperature. This increase occurred in darkness, but was strongly enhanced at high irradiances, probably as a consequence of increased rates of photosynthate exudation, stimulating respiratory processes in the mat. The compensation irradiance (Ec) marking the change of the mat from a heterotrophic to an autotrophic community, increased exponentially in this range of temperatures.     

Oxygen consumption and the composition of skeletal muscle tissue after training and inactivation in the European woodmouse (Apodemus sylvaticus)

Summary In European woodmice the amount and intensity of daily activity was compared to oxygen uptake and to the potential for oxidative metabolism of heart and skeletal muscle. One group of animals was inactivated by exposition to light during night time; another group of animals was trained by enforced running on a treadmill. The oxidative potential of the muscle tissue was assessed by morphometry of capillaries and mitochondria. A novel sampling technique was used which allowed us to obtain morphological data related to single muscles, to muscle groups, and finally to whole body muscle mass.Reducing the spontaneous activity by ten fold had no effect on oxygen uptake nor on capillaries or mitochondria in locomotory muscles. Mitochondrial volume was reduced, however, in heart and diaphragm. Enforced running increased the weight specific maximal oxygen uptake significantly. It also increased the mitochondrial volume in heart and diaphragm as well as in M. tibialis anterior. Capillary densities were neither affected by training nor by inactivation. A significant correlation was found between the capillary density and the volume density of mitochondria in all muscles analysed morphometrically. For the whole skeletal muscle mass of a European woodmouse the inner mitochondrial membranes were estimated to cover 30 m². The oxygen consumption per unit time and per unit volume of muscle mitochondrion was found to be identical in all groups of animals (4.9 ml O₂ min^–1 cm^–3).Symbols S _v (im,m) surface area of inner mitochondrial membranes per unit mitochondrial volume - V _v (mt, f) volume density of mitochondria (mitochondrial volume per fiber volume) - V (mt) total mitochondrial volume - V (f) muscle volume - N _A (c, f) capillary density - (f) mean fiber cross-sectional area     

Continuous microbial desulfurization of coal--application of a multistage slurry reactor and analysis of the interactions of microbial and chemical kinetics

Microbial desulfurization of coal by pyrite oxidizing bacterial enrichment cultures has been studied in air-agitated slurry reactors of 4- and 20-L volumes. Batch experiments showed that inoculation with an active bacterial culture is essential to minimize the lag phase, although a considerable number of pyrite oxidizing bacteria was found on the coal prior to desulfurization. For detailed investigations of kinetics, energy requirements, and technical applicability, a bioreactor equipment consisting of a cascade of eight stages was developed and operated continuously. Microbial desulfurization of coal-monitored by measuring the axial profile of dissolved iron concentration, real and maximum oxygen consumption rates, and cell concentration-at pulp densities to 30% was performed over a period of 200 days without any disturbances concerning the aeration system, fluidization, transport of solids and microbial growth. At a pulp density of 20%, a pyrite conversion of 68% was achieved after the third reactor stage at a total residence time of five days in the first three stages. The kinetics of pyrite degradation were found to be well described by a rate equation of first order in pyrite surface area concentration if the pyrite is directly accessible for microbial attack. Rate constants were determined to 0.48 mg pyrite/(cm(2) day) in the first and to 0.24 mg pyrite/(cm(2) day) in the following reactor stages. Kinetic models taking into account adsorption/desorption as well as growth kinetics failed to describe the observed reaction rates. However, a model treating pyrite degradation and microbial growth kinetics formalistically seems to be applicable when backmixing between the reactor stages can be avoided. The advantage of a multistage reactor in comparison to single-stage equipment was shown by calculation. To obtain a pyrite conversion of 68%, a three-stage reactor would require only 58% of the volume of single-stage equipment.Measurement of oxygen consumption rates proved to provide quickly and easily measurable parameters to observe microbial coal desulfurization in technical scale: the real oxygen consumption rate is correlated to the pyrite oxidation rate and the maximum oxygen consumption rate is correlated to the concentration of viable cells. The Y(o/s) coefficient for the amount of oxygen consumed per mass unit of pyrite oxygen was determined to approximately 0.33 in comparison to 1.0 which can be calculated from stoichiornetry. This could yet not be explained. Chemical leaching experiments as well as sulfur analyses of desulfurized coal samples showed that the microorganisms play the main role in degradation of pyrite from coal and that pyrite oxidation by ferric iron can be neglected.     

Effects of Flashes of Red or Blue Light on the Composition of Starved Chlorella pyrenoidosa

Autotrophically grown cells of Chlorella pyrenoidosa (211-8b) were starved 3 to 4 days in darkness, flashes of blue light, or flashes of red light. The blue flashes were sufficient to maintain the maximal rate of light-stimulated oxygen uptake during short term experiments. However, after 24 hours, the respiration rate in red flashes was equal to, or greater than, the rate in blue flashes. Starvation in darkness reduced the chlorophyll content by 11%, altered the blue absorbance of the nonsaponifiable material only 1 to 2%, and reduced the dry weight by 13%. Starvation in the presence of blue or red flashes reduced the dry weight by an additional 11 or 12% respectively. Protein per unit cell volume was not changed significantly during 3 to 4 days starvation in darkness or in blue flashes, even though dry weight per unit cell volume decreased 13% in darkness and 23% in blue flashes. In contrast, cells starved under red flashes showed a 20% decrease in protein per unit cell volume and a 24% decrease in dry weight per unit cell volume.     

Pulmonary diffusing capacity for nitric oxide during exercise in morbid obesity

Morbidly obese individuals may have altered pulmonary diffusion during exercise. The purpose of this study was to examine pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) during exercise in these subjects. Ten morbidly obese subjects (age = 38 +/- 9 years, BMI = 47 +/- 7 kg/m(2), peak oxygen consumption or VO(2peak) = 2.4 +/- 0.4 l/min) and nine nonobese controls (age = 41 +/- 9 years, BMI = 23 +/- 2 kg/m(2), VO(2peak) = 2.6 +/- 0.9 l/min) participated in two sessions: the first measured resting O(2) and VO(2peak) for determination of wattage equating to 40, 75, and 90% oxygen uptake reserve (VO(2)R). The second session measured pulmonary diffusion from single-breath maneuvers of 5 s each, as well as heart rate (HR) and VO(2) over three workloads. DLNO, DLCO, and pulmonary capillary blood volume were larger in obese compared to nonobese groups (P 0.10). The morbidly obese have increased pulmonary diffusion per unit increase in VA compared with nonobese controls which may be due to a lower rise in VA per unit increase in VO(2) in the obese during exercise.     

The scale-up of plant cell culture: Engineering considerations

The enormous versatility of plants has continued to provide the impetus for the development of plant tissue culture as a commercial production strategy for secondary metabolites. Unfortunately problems with slow growth rates and low products yields, which are generally non-growth associated and intracellular, have made plant cell culture-based processes, with a few exceptions, economically unrealistic. Recent developments in reactor design and control, elicitor technology, molecular biology, and consumer demand for natural products, are fuelling a renaissance in plant cell culture as a production strategy. In this review we address the engineering consequences of the unique characteristics of plant cells on the scale-up of plant cell culture.Abbreviations a gas-liquid interfacial area per volume - C dissolved oxygen concentration - C^* liquid phase oxygen concentration in equilibrium with the partial pressure of oxygen in the bulk gas phase - K_L overall mass transfer coefficient - k_L liquid film mass transfer coefficient - m_O2 cell maintenance coefficient for oxygen - OTR oxygen transfer rate - OUR oxygen uptake rate - pO₂ partial pressure of oxygen - STR stirred-tank reactor - v.v.m. volume of gas fed per unit operating volume of reactor per minute - X biomass concentration - Y_x/O2 biomass yield coefficient for oxygen - specific growth rate     

Lower temperature of the cauda epididymidis facilitates the storage of sperm by enhancing oxygen availability

The temperature coefficients for the oxygen consumption rate of sperm from the rat, mouse, bull, and sea urchin were measured to be within a range of 2.7 to 3.0. For a reduction in temperature from 37°C to 30°C, the respiration rate of mammalian sperm declined by a factor of approximately 2.1. Hence, the availability of oxygen to sustain these sperm substantially increased over this temperature range. In addition, the solubility of oxygen in cauda epididymidal fluid increased by 7.6% for a decline in temperature from 37°C to 30°C. The increased availability of oxygen to sperm at the lower temperature is related to the increased storage capacity of the cauda epididymidis in scrotal mammals. In this context, it is suggested that the evolutionary migration of the cauda epididymidis to a cooler, extra-abdominal location may have been influenced by the increased availability of oxygen to sperm and hence resulted in an increased capacity to sustain and thereby store more sperm per unit volume of duct.