Developmental Processes and Energetics (Concluded)

We investigated the effects of reduction of renal mass on rates of oxygen consumption, sodium transport, and indexes of oxidant stress in surviving nephrons. Rates of oxygen consumption in surviving nephrons were elevated by more than twofold compared with nephrons in intact kidneys in rats on standard protein intakes. Absolute rates of sodium reabsorption (TNa) in the surviving nephrons were increased with a lower ratio of TNa to oxygen consumption. To determine oxidant stress, we measured malondialdehyde (MDA) in the kidney and urine and the glutathione redox ratio in kidney tissue. MDA per nephron was increased in the subtotally nephrectomized model and was accompanied by increased absolute and fractional urinary excretion of MDA but not by an increase in kidney MDA per milligram protein. The glutathione redox ratios were similar. Since increased dietary protein intake worsens renal injury, we studied the effects of dietary protein manipulation (30 vs. 6%) on oxygen consumption, MDA levels, and the glutathione redox ratio. The kidneys of subtotally nephrectomized animals maintained on 30% protein diets exhibited increased rates of oxygen consumption. Increased dietary protein intake led to increased MDA per nephron, increased urinary excretion of MDA, and increased MDA per milligram protein in subtotally nephrectomized animals, and markedly increased the glutathione redox ratio. We conclude that, despite increased oxygen consumption, surviving nephrons compared with intact nephrons in rats on standard protein intake demonstrate no evidence of oxidant stress. Increased urinary clearance of MDA may provide a mechanism that prevents the buildup of lipid peroxidation. Subjecting the remnant nephron to increased protein increases oxygen consumption and imposes oxidant stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen consumption by eggs of European pond turtle was determined at two constant incubation temperatures of 25 and 28 degrees C during the second half of embryogenesis. During development at both temperatures, the rate of oxygen consumption initially increased to remain constant during the last quarter of embryogenesis. The difference between the rates of oxygen consumption at these temperatures decreased during the studied period. The coefficient Q10 for the rate of oxygen consumption decreased from 9 to 1.7. At an incubation temperature of 28 degrees C, the changes in the rate of oxygen consumption in response to a short-term temperature decrease to 25 degrees C or increase to 30 degrees C depended on the developmental stage and were most pronounced at the beginning of the studied period. During late embryonic and first 2.5 months of postembryonic development, the rate of oxygen consumption did not significantly differ after such temperature changes. The regulatory mechanisms formed during embryonic development are proposed to maintain the level of oxygen consumption during temperature changes.

Effects of oxygen diffusion and reaction kinetics in photodynamic therapy are considered in the context of a multicell tumour spheroid model. Steady-state measurements of oxygen made with a Clark-style microelectrode (4 mu m diameter tip) enable the authors to determine the rate of metabolic oxygen consumption and the oxygen diffusion coefficient in 500 mu m diameter EMT6/Ro spheroids. These values are 5.77 mu mol 1-1 s-1 and 1460 mu m2 s-1, respectively. Time-dependent electrode measurements of oxygen concentration during laser irradiation of individual Photofrin-sensitized spheroids are fitted to numerical solutions of a pair of diffusion-with-reaction equations. The analysis yields the rate of photodynamic oxygen consumption and a parameter that governs the oxygen sensitivity of photodynamic therapy. These experimentally derived quantities are used to calculate the temporal and spatial distributions of oxygen and the rate of oxygen consumption in a spheroid during irradiation at several fluence rates. The spatial distribution of photodynamic oxygen consumption is strongly fluence rate dependent. Using the experimental and theoretical results developed in this report, previously published survival data are analysed. The analysis indicates that the threshold dose of reacting singlet oxygen in the EMT6/Ro spheroid is 323+or-38 mu mol 1-1 (mean+or-SEM).

1. The average period of development of the Mud Turtle egg at 25.0 to 25.5° C. is 76 days; that of the Painted Turtle egg, 63 days; and that of the Snapping Turtle egg, 72 days. 2. Measurements of the carapace lengths of developing embryos of the Painted and Snapping Turtles indicated a relatively slow growth rate during early development, a rapid rise during the period between the thirtieth and sixtieth days, and almost no increase in length from the sixtieth day up to hatching. 3. The figures for the oxygen consumption of the developing eggs of the Mud Turtle, Painted Turtle and Three-toed Box Turtle agree closely and can be expressed by a single curve while those for the Snapping Turtle egg, though they give a fundamentally similar curve, show a significantly higher rate of metabolism. This is to be attributed to the greater bulk of the Snapper embryo. 4. During the first 50 days of development the oxygen consumption was a little less than doubled every 10 days; later on the curves flatten out. 5. While the increase in oxygen consumption is quite regular during the first 40 to 50 days of development irregular values were obtained at later stages, probably as a result of muscular activity of the embryos. 6. Young hatched turtles have about the same rate of oxygen consumption as do advanced embryos. The highest values for oxygen consumption were obtained from eggs studied while in the process of hatching. 7. The eggs of the Snapping Turtle, Painted Turtle and Three-toed Box Turtle showed a definite water intake during development as evidenced by a progressive weight increase but no such phenomenon was found in the case of the Mud Turtle egg. 8. The Snapping Turtle egg shows an average loss, during development, of 0.46 gram of dry substance. Fat is consumed in the amount of 61 mg. per egg. These data in conjunction with those on the oxygen consumption make it appear possible, though not yet certain, that large amounts of protein are catabolized during the development of this animal.

The combined effects of temperature and salinity on the rate of oxygen consuption by the estuarine crab Panopeus herbstii Milne-Edwards (Crustacea: Decapoda: Xanthidae) were studied. Crabs were acclimated to all combinations of 10° and 23°C and 5 and 30% S. The rate of oxygen consumption was measured at 10° and 25°C in experimental salinities of 5, 15, 30, and 40%. Following acclimation to 23°C and 5% S, the rate of oxygen consumption by female crabs was significantly lower than that of males. No other experimental treatments resulted in significant rate differences between males and females. The anticipated response of an increase in oxygen consumption upon exposure of this euryhaline crab to low salinity occurred. Similarly, compensatory adjustment to low temperature following acclimation was evidenced. However, unpredictable patterns of response were elicited by specific experimental manipulations of temperature and salinity. Thermal sensitivity of oxygen uptake as reflected by Q10 was also influenced by experimental conditions and further substantiated the occurrence of interactions between temperature and salinity.

Walking performance and aerobic and anaerobic metabolism of Carcinus maenas (L.) in sea water at 15°C

Acute injections of melanocortin (MC) agonist and antagonist are highly effective in reducing or increasing food take, respectively. Much less is known about how injection of MC receptor active substances affects metabolism, in particular during long term administration. Here we investigated the effect of 8 days continuous i.c.v. infusion of either MC receptor agonist MTII or the selective MC4 receptor antagonist HS024 on oxygen consumption, food intake and body weight in rats. We observed significant increase in oxygen consumption 2 days after the start of the MTII infusion. However, this increase had disappeared by day 4 of the study. No difference was observed in the oxygen consumption after injection of HS024. MTII substantially decreased the food intake during the first days, but then the feeding recovered and the body weight stabilised at a new level. The immediate effect of the MC receptor agonist on both food intake and metabolism was thus transient, even though the weight loss was maintained. The HS024 treated rats were hyperphagic throughout the test period, continuously gaining weight, resulting in increased fat pads and high leptin levels. This is the first study that describes long term effects of MC receptor agonist and antagonist on metabolism and energy balance.

Near-infrared spectroscopy (NIRS) allows for non-invasive measurement of oxy- and deoxy-hemoglobin content in skeletal muscle (SM) and can be used to measure SM oxygen consumption rate. However, scarce studies have evaluated the relationship between SM and whole-body O2 consumption rates. PURPOSE: The purpose of our study was to investigate the relationship between NIRS-derived SM O2 consumption rate (mVO2) and whole-body O2 consumption (wbVO2) at rest and while walking. METHODS: mVO2 was measured by placing a NIRS device on the belly of the medial gastrocnemius (MG) of the participant’s dominant leg (N = 26, 25 ± 8 years old). A pneumatic rapid inflation cuff was placed proximal to the testing site for occlusion of arterial blood flow. After a 5-minute rest while lying supine, average resting mVO2 was measured during three rounds of 30s arterial occlusion and 30s of rest. Ambulatory mVO2 was measured during a 10s arterial occlusion immediately following 6 minutes (group 1, N = 12) or 5 minutes (group 2, N = 14) of walking at usual gait speed over a 40 m course. In group 1, whole-body oxygen consumption (wbVO2) rate was measured during 15 minutes of rest by indirect calorimetry and during ambulation by portable indirect calorimetry. In group 2, wbVO2 rate was measured during rest (10 minutes) and ambulation by portable indirect calorimetry. The association between wbVO2 rate and mVO2 rate was modeled through linear regression analysis, adjusted for group and muscle tissue thickness. RESULTS: At rest, a significant positive association (β = 11.1, P < 0.001) was observed between mVO2 (mean: 0.27 ± 0.07%/s) and wbVO2 (mean:3.7 ± 0.8 mL/kg/min). Similarly, a significant positive association (β = 1.1, P < 0.05) was observed between walking mVO2 (mean: 6.7 ± 2.5%/s) and walking wbVO2 (mean: 13.9 ± 3.2 mL/kg/min). CONCLUSION: An association between whole-body and muscle oxygen consumption rate was detected both at rest and during ambulation. These findings suggest the use of NIRS to accurately assess SM metabolism and potential changes to SM metabolism that may occur as a result of disease, muscle damage, or training/rehabilitation. Supported by: Supported by Towson University College of Health Professions Summer Undergraduate Research Institute.

Oxygen consumption in unfertilized salmonid eggs: an indicator of egg quality?

1. Experiments measuring the rate of oxygen consumption of unanaesthetized new-born rabbits and the blood flow in brown adipose tissue of anaesthetized new-born rabbits are described.2. The increase in rate of oxygen consumption caused by I.V. infusion of noradrenaline, adrenaline and isoprenaline (2 mug/kg.min for 10 min) was blocked by propranalol (I.V. 1 mg/kg) but the increase caused by cold exposure was not. A larger dose of propranalol (5 mg) blocked the calorigenic response to cold exposure as well.3. Infusion of glucagon (I.V. 4 mug/kg.min for 10 min) caused a large increase in the rate of the rabbit's oxygen consumption and in blood flow through its brown adipose tissue. These responses, which reached a maximum within 10 min from the start of the infusion, were not blocked by propranalol (1 or 5 mg/kg).4. Infusion of corticotrophin (I.V. 1 i.u./kg.min for 10 min) also caused a large increase in the rate of oxygen consumption of new-born rabbits. The response reached a maximum about 20 min from the start of the infusion and it was not blocked by propranalol (5 mg/kg).5. These results support the conclusion that noradrenaline is released at sympathetic endings in brown adipose tissue and that the increase in blood flow caused by noradrenaline is secondary to its metabolic action on the tissue. They also suggest the possibility that glucagon and corticotrophin may act directly on brown adipose tissue and stimulate heat production during cold exposure.

1. Rectal temperature and the rate of oxygen consumption in the new-born pig were measured following the subcutaneous injection of L-thyroxine.2. Thyroxine stimulated oxygen consumption during the post-natal period; both immediate and latent increases were observed.3. The immediate effect occurred after thyroxine, 80 mug/kg, in suckled pigs aged 1-11 days; it was most marked at about 1-4 days of age with a peak increase (20%) in oxygen consumption and a rise in rectal temperature at about 4 hr following the injection.4. The peak increase (30%) in oxygen consumption associated with the latent effect of three successive daily injections of thyroxine, 300 mug/kg, occurred at 5-7 days of age, whether the pigs were first injected at 1 or at 4 days of age.5. It is concluded that there is a high sensitivity to thyroxine in the pig during the first week after birth, when the hormone is not bound to plasma proteins to the same degree as in the older animal.

Oxygen consumption rate (OCR) and generation of superoxide and nitric oxide (NO) in mouse aortic endothelial cells (MAECs) treated with lipopolysaccharide (LPS) were studied. The OCR was determined in cell suspensions at 37 degrees C by electron paramagnetic resonance (EPR) spectroscopy. LPS significantly altered the OCR in a dose and time-dependent fashion. The OCR was significantly elevated immediately following the treatment of MAECs with LPS (5 and 10 microg/ml) and NADPH (100 microM) whereas the same was depressed 1 h after exposure to similar conditions of incubation. Under similar experimental conditions, superoxide generation was also determined by EPR spectroscopy and cytochrome c reduction assays. A marginal increase in the superoxide production was observed when the cells were treated with LPS and NADPH alone whereas the same was further enhanced significantly when the cells were treated with LPS and NADPH together. The increase in oxygen consumption and superoxide production caused by LPS was inhibited by diphenyleneiodonium (DPI), suggesting the involvement of NAD(P)H oxidase. A significant increase in the NO production by MAECs was noticed 1 h after treatment with LPS and was inhibited by L-NAME, further suggesting the involvement of nitric oxide synthase (NOS). Thus, on a temporal scale, LPS-induced alterations in oxygen consumption by MAECs may be under the control of dual regulation by NAD(P)H oxidase and NOS.

Basal oxygen consumption of isolated photophores from Porichthys sp. at rest, i.e. without light emission, increased significantly from 0.101±0.021nmolmin−1 to 0.173±0.016nmolmin−1 in response to the addition of 5.5mmol l−1 glucose. 5.5mmol l−1 glucose pretreatment modified the time course of the two phases of adrenaline-induced luminescence; an increase in oxygen consumption was observed during the fast phase of light production but a decrease occurred during the slow phase of luminescence. Pretreatment of isolated photophores with 5.5mmol l−1 glucose totally inhibited the light emission induced by 1mmol l-1 potassium cyanide. With this treatment, the respiration rate decreased progressively and after 40min reached a value not significantly different from zero. Even after blockage of cellular respiration by cyanide, an increase in the rate of oxygen consumption was observed during the fast adrenaline-induced luminescence. Glucose utilisation by glycolysis or by oxidative metabolism may provide energy to an inhibitory mechanism that maintains the photophores in a non-luminescent state. We suggest that the oxygen consumed during the fast phase of adrenaline luminescence could represent the activity of an extramitochondrial oxidative pathway involved in the light reaction.

Sodium transport and oxygen consumption have been simultaneously studied in the short-circuited toad skin. A constant stoichiometric ratio was observed in each skin under control condition (NaCl-Ringer's solution bathing both sides of the skin) and after block of sodium transport by ouabain. During alterations of sodium transport by removal and addition of K to the internal solution the stoichiometric ratio is constant although having a value higher than that observed in other untreated skins. The coupling between active sodium transport and oxygen consumption was studied after a theoretical nonequilibrium thermodynamic model. Studies were made of the influence of Na chemical potential difference across the skin on the rates of Na transport and oxygen consumption. A linear relationship was observed between the rates of Na transport and oxygen consumption and the Na chemical potential difference. Assuming the Onsager relationship to be valid, the three phenomenological coefficients which describe the system were evaluated. Transient increases in the rate of sodium transport and oxygen consumption were observed after a transitory block of sodium transport by removal of Na from the external solution. Cyanide blocks completely the rate of oxygen consumption in less than 2 min and the short-circuit current measured after that time decays exponentially with time, suggesting a depletion of ATP from a single compartment.

Fishes undergo dramatic physiological changes upon consumption of a meal, including an increase in oxygen consumption to support the metabolic cost of digestion [specific dynamic action (SDA)] and an increase in the excretion of ammonia. Channel catfish (Ictalurus punctatus) and blue catfish (I. furcatus) are two species commonly used for commercial aquaculture production in the United States. Postprandial ammonia excretion and oxygen consumption of both channel and blue catfish were measured at 25 and 32°C. Rates of both ammonia excretion and oxygen consumption increased quickly after feeding and were significantly higher within 2 h postfeeding. Ammonia excretion of channel catfish peaked 6 h postfeeding at both 25 and 32°C, with peak ammonia excretion rates increasing 8.3‐ and 4.7‐fold higher than fasting rates at 25 and 32°C, respectively. Ammonia excretion of blue catfish at 25°C peaked 6.6‐fold higher than fasting rates at 12 h postfeeding and 5.5‐fold higher than fasting rates 6 h postfeeding at 32°C. Relative to fasting levels, postprandial oxygen consumption of channel catfish peaked 1.8‐ and 2.0‐fold higher at 25 and 32°C, respectively. Blue catfish oxygen consumption peaked 1.9‐ and 1.8‐fold higher at 25 and 32°C, respectively. Both channel and blue catfish rapidly increase ammonia excretion and oxygen consumption in response to feeding, with temperature mostly affecting changes in peak and minimum rates.