Quantitative aspects of oxygen and carbon dioxide exchange through the lungs in Ocypode ceratophthalmus (Crustacea: Decapoda) during rest and exercise in water and air

Ghost crabs Ocypode ceratophthalmus were exercised in air and water to measure CO₂ and O₂ exchange rates using the method of instantaneous measurements of oxygen consumption rate (MO₂) where applicable. Average heart rate increased from 100 to nearly 400 pulses per minute after five minutes of exercise on a treadmill at a run rate of 0.133 m s^?1. It took less than a minute for oxygen taken up through the lung epithelium from the air inside the branchial cavity to reach the maximal oxygen consumption rate of 26.1 mmol O₂ kg^?1 h^?1. Resting MO₂ was 4.06 mmol O₂ kg^?1 h^?1 in air, but decreased to 3.37 mmol O₂ kg^?1 h^?1 in seawater. Radioactive CO₂ from injected l-lactate is released linearly by the lung. The percent accumulated 14-CO₂ in exhaled air, plotted against time, intersects zero time on the x -axis, indicating rapid gas exchange at the lung surface. The P ₅₀ values for native haemocyanin of 4.89 mm Hg before exercise, and 8.99 mm Hg after exercise, are typical of a high-affinity haemocyanin usually associated with terrestrial crabs. The current notion that Ocypode ceratophthalmus drown when submerged in seawater was not substantiated by our experiments. MO₂ in seawater increased from 3.37 mmol O₂ kg^?1 h^?1 for resting crabs to 5.72 mmol O₂ kg^?1 h^?1 during exercise. When submerged by wave-seawater in the natural environment and during exercise in respirometer-seawater O. ceratophthalmus do not swim but, having a specific density of 1.044, float nearly weightless with a minimum of body movements.     

Ventilation and oxygen consumption in the hagfish, Myxine glutinosa L.

Ventilation was measured directly in the hagfish, Myxine glutinosa L., by means of an electro-magnetic blood flowmeter. Ventilatory flow and frequency increased from 0.86 ± 0.27 ml·min^?, and 18.2 ± 5.1·min^?, respectively, at 7°C to 1.70 ± 0.20 ml·min^?, and 70.1 ± 9.5·min^? at 15 ·C.Standard oxygen consumption,V?O₂, was measured in non-buried hagfish. V?O₂ was 0.57 ± 0.17μl O₂·g^?1·min^?1 at 7°C, and 0.85 ± 0.12μl O₂·g^?1·min^?1 at 15°C.     

Aerial and Aquatic Respiration in the River Crab Potamonautes Warreni Calman with Notes on Gill Structure

Summary

The oxygen consumption rate (?O₂) for Potamonauteus warreni Calman (= Potamon warreni (Calman) kept in 25 °C water was 34,4 μmol 1^?1 O₂ kg^?1 and after 72 hours in 98% R.H. air the rate was 31,9 μmol 1^?1 O₂ kg^?1 min^?1. The ?O₂ values for each of the two groups are not significantly different (P > 0,05). The partial oxygen tension of pre-branchial (v = venous) haemolymph (P_vCO₂) is 15,3 mm Hg in water and 13,0 mm Hg in air); partial carbon dioxide tension of pre-branchial (v) haemolymph (P_vCO₂) is 13,2 mm Hg in water and 13,0 mm Hg in air); the total carbon dioxide concentration in pre-branchial (v) haemolymph (C_vCO₂) tot. is 12,3 mmol 1^?1 in air and 13,9 mmol 1^?1 in water) are not significantly different for the two groups (P > 0,05). The haemolymph pH and the lactate concentration for crabs in water was found to be 7,51 and 0,38 mmol 1^?1 respectively. No significant differences were found in pre-branchial haemolymph oxygen tension, carbon dioxide tension, total carbon dioxide content, haemolymph pH, lactate level, chloride concentration, P₅₀ and haemocyanin-oxygen cooperativity in control crabs kept in water, and experimental crabs held in air for 72 hours. The chloride concentration, (327,0 mmol 1^?1) for crabs kept in water does not differ from that of crabs held in air for 72 hours but is at least 15% higher than the sodium concentration (255 mmol 1^?1) for crabs kept in water. The gill surface area is 520 mm² g^?1 wet body mass; on average 9,2 gill platelets (lamellae) can be found on a gill length of one millimetre. Each lamella is spaced 60–70 μm apart, each with a thickness of 30–40 μm. It is concluded that P. warreni may be described as a truly amphibious fresh-water crab.     

Soil nitrogen transformations under Populus tremuloides, Betula papyrifera and Acer saccharum following 3 years exposure to elevated CO2 and O3

Increases in atmospheric CO₂ and tropospheric O₃ may affect forest N cycling by altering plant litter production and the availability of substrates for microbial metabolism. Three years following the establishment of our free‐air CO₂–O₃ enrichment experiment, plant growth has been stimulated by elevated CO₂ resulting in greater substrate input to soil; elevated O₃ has counteracted this effect. We hypothesized that rates of soil N cycling would be enhanced by greater plant productivity under elevated CO₂, and that CO₂ effects would be dampened by O₃. We found that elevated CO₂ did not alter gross N transformation rates. Elevated O₃ significantly reduced gross N mineralization and microbial biomass N, and effects were consistent among species. We also observed significant interactions between CO₂ and O₃: (i) gross N mineralization was greater under elevated CO₂ (1.0 mg N kg^?1 day^?1) than in the presence of both CO₂ and O₃ (0.5 mg N kg^?1 day^?1) and (ii) gross NH₄⁺ immobilization was also greater under elevated CO₂ (0.8 mg N kg^?1 day^?1) than under CO₂ plus O₃ (0.4 mg N kg^?1 day^?1). We used a laboratory ¹⁵N tracer method to quantify transfer of inorganic N to organic pools. Elevated CO₂ led to greater recovery of NH₄⁺‐¹⁵N in microbial biomass and corresponding lower recovery in the extractable NO₃^? pool. Elevated CO₂ resulted in a substantial increase in NO₃^?‐¹⁵N recovery in soil organic matter. We observed no O₃ main effect and no CO₂ by O₃ interaction effect on ¹⁵N recovery in any soil pool. All of the above responses were most pronounced beneath Betula papyrifera and Populus tremuloides, which have grown more rapidly than Acer saccharum. Although elevated CO₂ has increased plant productivity, the resulting increase in plant litter production has yet to overcome the influence of the pre‐existing pool of soil organic matter on soil microbial activity and rates of N cycling. Ozone reduces plant litter inputs and also appears to affect the composition of plant litter in a way that reduces microbial biomass and activity.     

Heterogeneous Catalytic Oxidation of Phenanthrene by Hydrogen Peroxide in Soil Slurry: Kinetics,Mechanism, and Implication

The degradation of phenanthrene sorbed on soil has been carried out using a H₂O₂/goethite heterogeneous catalytic oxidation process. The effect of operating variables, such as the goethite concentration, pH, H₂O₂ concentration, soil organic matter, and bicarbonate ions has been investigated. The reaction followed pseudo-first order kinetics. The rate constants were evaluated and varied between 2.0×10^?4 and 1.1×10^?3?min^?1 depending on the H₂O₂ concentration. The highest rate of degradation of phenanthrene was observed at a H₂O₂ concentration of 5?M and 134.0?g/kg goethite. The intermediate product formed during the degradation of phenanthrene was identified to be salicylic acid that finally degraded to CO₂ and H₂O. H₂O₂ consumption continued as the OH radical attacked the salicylic acid. More than 80% consumption of the 5?M H₂O₂ took place within 30?min, and the degradation was almost complete after 3?h of reaction. Neutral pH was found to be effective in the removal of phenanthrene. Both soil organic matter (SOM) and bicarbonate ions in the soil inhibited the oxidation rate of phenanthrene.     

Measurements of aerobic metabolism of a school of horse mackerel at different swimming speeds

Oxygen consumption rates were measured in a school of 56 horse mackerel Trachurus trachurus while at rest and while swimming at steady sustained speeds. Resting values of 38.76 and 42.10mg O₂ kg^?1 h^?1 were measured in a sealed cylindrical tank (535 l) while observing that the fish school remained neutrally buoyant and inactive with only gentle pectoral fin movements and no swimming motion. The same school was trained to swim with projected light patterns within a 10-m diameter annular doughnut respirometer. The oxygen consumption increased from the resting level through 51 mg O₂ kg^?1 h^?1 at the slowest swimming speeds of 0.29 m s^?1 (0.95 L s^?1) to around 259 mg O₂ kg^?1 h^?1 at the higher measured swimming speed of 0.87 m s^?1 (2.82 L s^?1). The data fitted a curve where oxygen consumption rose in proportion to velocity to the power of 2.56 with the intercept at the resting level. The maximum sustained speed (80 min) of 1.12 m s^?1 (3.63 Ls^?1) was not achieved within the respirometer but corresponded to an estimated oxygen consumption of 458.33 mg O₂ kg^?1 h^?1 giving a scope for aerobic activity of 419.02 mg O₂ kg^?1 h^?1. At a speed of 0.87 m s^?1, there was a lower bound on the aerobic efficiency of at least 38% and at 1.12 m s^?1, the highest aerobic speed, of 40%. Sustained speeds swum in a curved path as here should be increased by 5% for a straight path giving a maximum sustained 80 min speed of 1.18 m s^?1.     

Metabolism,thermogenesis and daily rhythm of body temperature in the wood lemming,Myopus schisticolor

Wood lemmings (Myopus schisticolor) were captured during their autumnal migration in September and October. The animals were maintained at 12°C and under 12L:12D photoperiod. Basal metabolic rate and thermogenic capacity of the wood lemming were studied. Basal metabolic rate was 3.54 ml O₂·g^-1·h^-1, which is 215–238% of the expected value. The high basal metabolic rate seems to be typical of rodents living in high latitudes. The body temperature of the wood lemming was high (38.0–38.8°C), and did not fluctuate much during the 24-h recording. The high basal metabolic rate and the high body temperature are discussed with regard to behavioural adaptation to a low-quality winter diet. Thermogenic capacity, thermal insulation and non-shivering thermogenesis of the wood lemming displayed higher values than expected: 53.0 mW·g^-1, 0.53 mW·g^-1·C^-1 and 53.2 mW·g^-1, respectively. Brown adipose tissue showed typical thermogenic properties, although its respiratory property was fairly low, but mitochondrial protein content was high compared to other small mammals. The 24-h recording of body temperature and motor activity did not reveal whether the wood lemming is a nocturnal animal. Possibly, the expression of a circadian rhythm was masked by peculiar feeding behaviour. It is concluded that the wood lemming is well adapted to living in cold-temperature climates.Abbreviations BAT brown adipose tissue; bm, body mass - BMR basal metabolic rate - C conductance - Cox cytochrome-c-oxidase - HP heat production - HP_max maximum heat production - M metabolism - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - T _a anibient temperature - T _b body temperature - T _lc lower critical temperature - UCP uncoupling protein - vO₂ oxygen consumption - vO_{2 max} maximum oxygen consumption     

Bimodal oxygen uptake in a freshwater air-breathing fish,Notopterus chitala

Measurements of bimodal oxygen uptake have been made in a freshwater air-breathing fish,Notopterus chitala at 29.0±1(S.D.)°C. xhe mean oxygen uptake from continuously flowing water without any access to air, was found to be 3.58±0.37 (S.E.) ml O₂ · h^?1 and 56.84+4.29 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish weighing 66.92 + 11.27 (S.E.) g body weight. In still water with access to air, the mean oxygen uptake through the gills were recorded to be 2.49 ± 0.31 (S.E.) ml O₂ · h^?1 and 38.78 ± 1.92 (S.E.) ml O₂ · kg^?1 · h^?1 and through the accessory respiratory organs (swim-bladder) 6.04±0.87 (S.E.) ml O₂ · h^?1 and 92.32±2.91 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish averaging 66.92±11.27 (S.E.) g. Out of the total oxygen uptake (131.10 ml O₂ · kg^?1 · h^?1), about 70% was obtained through the aerial route and the remainder 30% through the gills.     

Direct evidence for the presence of a rotenone-resistant NADH dehydrogenase on the inner surface of the inner membrane of plant mitochondria

Submitochondrial particles (SMP) were produced from Jerusalem artichoke (Helianthus tuberosus L.) mitochondria by sonication and differential centrifugation. The SMP were about 50% inside-out as measured by the access of reduced cytochrome c to cytochrome c oxidase. Uncoupled NADH oxidation (1 mM NADH) by the SMP was 120 nmol O₂ min^?1mg^?1, which was reduced to 98 nmol O₂ min^?1 (mg mitochondrial protein)^?1 in the presence of EGTA. In contrast, the oxidation of NADH by intact mitochondria was completely inhibited by EGTA (from 182 to 14 nmol O₂ min^?1mg^?1). The EGTA-resistant NADH oxidation by the SMP is ascribed to the NADH dehydrogenase(s) on the inside of the inner membrane and exposed to the medium in the inside-out SMP. In the presence of EGTA it could be shown that two NADH dehydrogenase activities were present in the SMP. One had an apparent K_m of 7 μM for NADH, a V_max of 80 nmol NADH min^?1mg^?1, and was rotenone-sensitive. This dehydrogenase is equivalent to the mammalian Complex I NADH dehydrogenase. The other dehydrogenase, which was rotenone-resistant, had a K_m of 80 μM and a V_max of 131 nmol NADH min^?1mg^?1; it is probably responsible for the rotenone-resistant oxidation of organic acids often observed in plant mitochondria. The redox poise of the pyridine nucleotides had only a small effect on the relative rates of the two internal dehydrogenases. Electron flow through these dehydrogenases appears, therefore, to be regulated mainly by the concentration of NADH in the matrix of the mitochondria.     

The effect of feeding on CO2 production and energy expenditure in ponies measured by indirect calorimetry and the 13C-bicarbonate technique

Energy expenditure (EE) can be estimated based on respiratory gas exchange measurements, traditionally done in respiration chambers by indirect calorimetry (IC). However, the ¹³C-bicarbonate technique (¹³C-BT) might be an alternative minimal invasive method for estimation of CO₂ production and EE in the field. In this study, four Shetland ponies were used to explore the effect of feeding on CO₂ production and EE measured simultaneously by IC and ¹³C-BT. The ponies were individually housed in respiration chambers and received either a single oral or intravenous (IV) bolus dose of ¹³C-labelled sodium bicarbonate (NaH¹³CO₃). The ponies were fed haylage 3 h before (T₋₃), simultaneously with (T₀) or 3 h after (T₊₃) administration of ¹³C-bicarbonate. The CO₂ produced and O₂ consumed by the ponies were measured for 6 h with both administration routes of ¹³C-bicarbonate at the three different feeding times. Feeding time affected the CO₂ production (P<0.001) and O₂ consumption (P<0.001), but not the respiratory quotient (RQ) measured by IC. The recovery factor (RF) of ¹³C in breath CO₂ was affected by feeding time (P<0.01) and three different RF were used in the calculation of CO₂ production measured by ¹³C-BT. An average RQ was used for the calculations of EE. There was no difference between IC and ¹³C-BT for estimation of CO₂ production. An effect of feeding time (P<0.001) on the estimated EE was found, with higher EE when feed was offered (T₀ and T₊₃) compared with when no feed was available (T₋₃) during measurements. In conclusion, this study showed that feeding time affects the RF and measurements of CO₂ production and EE. This should be considered when the ¹³C-BT is used in the field. IV administration of ¹³C-bicarbonate is recommended in future studies with horses to avoid complex ¹³C enrichment-time curves with maxima and shoulders as observed in several experiments with oral administration of ¹³C-bicarbonate.     

Gas exchange and energy metabolism of the ostrich (Struthio camelus) embryo

We measured oxygen consumption ( ) and carbon dioxide emission ( ) rates, air-cell gas partial pressures of oxygen (P_AO₂) and CO₂ (P_ACO₂), eggshell water vapour conductance and energy content of the ostrich (Struthio camelus) egg, ‘true hatchling’ and residual yolk, and calculated RQ and total oxygen consumption ( ) for ostrich eggs incubated at 36.5°C and 25% relative humidity. The pattern showed a drop of approximately 5% before internal pipping. just prior to internal pipping agrees with allometric calculations. Despite the higher incubation temperature compared to other studies, and the resultant shorter incubation duration (42 days), (91.7 l kg⁻¹) was similar to a previously reported value. RQ values during the second half of incubation (approx. 0.68) were lower than expected for lipid catabolism. Prior to internal pipping, P_AO₂ and P_ACO₂ were 98 and 48.3 torr (13.1 and 6.4 kPa), respectively. The growth pattern of the ostrich embryo is different from the typical precocial pattern, showing a time delay in the rapid growth phase. As a result, the lowered overall energy expenditure for tissue maintenance, as compared to other species, is reflected in the low yolk utilization and high residual yolk fraction of the whole hatchling dry mass. These could also result from the relatively short incubation period of the ostrich egg, thereby evading desiccation by excess water loss.     

Design and Performance of Rechargeable Sodium Ion Batteries,and Symmetrical Li‐Ion Batteries with Supercapacitor‐Like Power Density Based upon Polyoxovanadates

The polyanion Li₇V₁₅O₃₆(CO₃) is a nanosized molecular cluster (≈1 nm in size), that has the potential to form an open host framework with a higher surface‐to‐bulk ratio than conventional transition metal oxide electrode materials. Herein, practical rechargeable Na‐ion batteries and symmetric Li‐ion batteries are demonstrated based on the polyoxovanadate Li₇V₁₅O₃₆(CO₃). The vanadium centers in {V₁₅O₃₆(CO₃)} do not all have the same V^IV/V redox potentials, which permits symmetric devices to be created from this material that exhibit battery‐like energy density and supercapacitor‐like power density. An ultrahigh specific power of 51.5 kW kg^?1 at 100 A g^?1 and a specific energy of 125 W h kg^?1 can be achieved, along with a long cycling life (>500 cycles). Moreover, electrochemical and theoretical studies reveal that {V₁₅O₃₆(CO₃)} also allows the transport of large cations, like Na⁺, and that it can serve as the cathode material for rechargeable Na‐ion batteries with a high specific capacity of 240 mA h g^?1 and a specific energy of 390 W h kg^?1 for the full Na‐ion battery. Finally, the polyoxometalate material from these electrochemical energy storage devices can be easily extracted from spent electrodes by simple treatment with water, providing a potential route to recycling of the redox active material.     

Acute effects of Cu on oxygen consumption and 96 hr-LC50 values in the freshwater fish Tilapia sparrmani (Teleostei: Cichlidae) in Mooi River hard water,South Africa

The median lethal copper (Cu) concentration (96 hr-LC₅₀) values for acute Cu toxicity for Tilapia sparrmanii (live mass: 30 ± 8g) in Mooi River hard water of dolomitic origin at 20 °C, pH 7.9, was 68.1 μmol l^?1. At this 96 hr-LC₅₀ value the specific oxygen consumption rate (∈ O₂) decreased by 44.2 (± 2.1) % from a non-exposed value of 6.6 (±0.32) mmol O₂ kg^?1 hr^?1 to 3.63 (±0.23) mmol O₂ kg ^?1 hr^?1. At 46.4 μmol Cu l^?1, 100% of the exposed T. sparrmanii were still alive after 96 hours, but the ∈ O₂ decreased by a mean value of 1.65 (± 0.16) mmol O₂ kg^?1 fish hr^?1 or 25% (± 2.4). Contrary to Pb and Cd, Cu as CuCl₂ 2H₂O was not precipitated in hard water four days after it was dissolved. Thus T. sparrmanii and other cichlids are shown to be more than an order of magnitude more resistant to Cu as a toxicant than most salmonids.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Daily Rhythms of Metabolic Rate and Body Temperature of Two Murids from Extremely Different Habitats

Daily circadian rhythms of body temperature (T_b) and oxygen consumption (VO₂) were measured in two murid species, which occupy extremely different habitats in Israel. The golden spiny mouse (Acomys mssalus) is a diurnal murid distributed in arid and hot parts of the great Syrio-African Rift Valley, while the broad-toothed field mouse (Apodeinns mystacinus) is a nocturnal species that inhabits the Mediterranean woodlands. In both species, the daily rhythms of T_b and VO₂ are entrained by the photoperiod. Under laboratory experimental conditions (ambient temperature T_a = 33^oC and photoperiod regime of 12L: 12D), Acomys russatus exhibits a tendency towards a nocturnal activity pattern, compared to the diurnal activity displayed by this species under natural conditions. Under the same photoperiod regime and at T_a = 28^oC, Apodemus mystacinus displays nocturnal activity, as observed under natural conditions. The maximal values of T_b were recorded in Acomys russatus at midnight (23:50 h), while the maximal values of VO₂ were recorded at the beginning of the dark period (18:20 h). In Apodemus mystacinus, the maximal values of T_b and VO₂ were recorded at 23:40 and 20:00 h, respectively. The ecophysiological significance of these results is discussed further.     

In situ plankton community respiration measurements show low respiratory quotients in a eutrophic lake

Planktonic community respiration is an important carbon cycling process, typically quantified by converting measured values of dissolved O₂ consumption rates into CO₂ production rates assuming a respiratory quotient of 1 (RQ = CO₂ per O₂ by moles). However, the true variability in planktonic RQs between different aquatic ecosystems is poorly understood. We conducted in situ RQ measurements in a eutrophic lake dominated by algal-derived substances and found that RQs were significantly below 1. In fact, many RQ values were extremely low (0.2–0.6), below theoretical RQs for oxidation of algal organic matter substrates (0.7–0.8), suggesting that other factors than substrate control need to be considered to understand the RQ. This view was further supported by lack of correlations between RQ and microbial variables known to be strongly substrate dependent, including bacterial growth efficiency and the functional capacity of the bacterioplankton community to degrade different compounds. Based on the measured dynamics in methane and nutrient pools, we discuss that methane oxidation and nitrification likely occurred in the lake, contributing to the unusually low RQs. Our findings demonstrate that planktonic RQs in productive lakes can systematically be below 1, suggesting that CO₂ emissions from these lakes may currently be overestimated.     

Simultaneous telemetric monitoring of the circadian changes in core and BAT temperature in rats: Endogenous vasopressin may contribute to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle

The purpose of the present study was to analyze simultaneously the temporal relationship between the changes of circadian rhythms of brown adipose tissue (BAT) thermogenesis and core temperature (T_c) by dual probe telemetric monitoring transmitters and to determine the role of endogenous arginine vasopressin (AVP) in the circadian rhythms of BAT temperature (T_BAT) and T_c in male rats. The key observations in this study are: (1) Increase in T_BAT commenced approximately 8 min before T_c increases at the start of transition from the light to dark phase. Whereas at the start of transition from the dark to light phase, decrease in T_BAT commenced approximately 3 min before T_c decreases. The data show that circadian changes of BAT thermogenesis do indeed play a significant role in the overall maintenance of the circadian rhythm of core temperature. (2) The plasma AVP level was significantly elevated when core temperature decreases during the light phase, suggesting that endogenous AVP is involved in thermoregulatory processes during the light phase. V1a receptor antagonist could elevate core and BAT temperature during the light period, suggesting that endogenous AVP, acting through V1a receptor, could be involved in tonic thermoregulatory processes.V1a receptor antagonist can increase the blood lipid metabolism, suggesting that the mechanism of endogenous AVP in tonic thermoregulatory processes during light period could involve the suppression of lipolysis in BAT and other peripheral tissues. In summary, this study demonstrated that endogenous vasopressin contributes to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle.     

Pulmonary diffusing capacity in reptiles (Relations to temperature and O2-uptake)

Summary Pulmonary CO-diffusing capacity (D l _CO), lung volume, pulmonary perfusion and O₂-uptake were measured by non-invasive techniques in the lizardsVaranus exanthematicus andTupinambis teguixin (mean body weight 2.2 kg for both species).The CO-diffusing capacity was at 25–27°C 0.059 mlstpd·kg^–1·min^–1·Torr^–1 inVaranus, which is 47% greater than the value of 0.040 mlstpd·kg^–1·min^–1·Torr^–1 inTupinambis. The lung volume ofVaranus was 36 ml·kg^–1 and that ofTupinambis 20 ml·kg^–1. At 35–37°C the diffusing capacity of lizard lungs are about 25% of those for mammals of comparable size.InVaranus pulmonary CO-diffusing capacity increased with temperature from 0.027 mlstpd·kg^–1·min^–1·Torr^–1 at 17–19 °C to 0.075 mlstpd·kg^–1·min^–1·Torr^–1 at 35–37 °C. This change closely matched a concomitant increase of O₂-uptake. Pulmonary perfusion increased from 27 ml·kg^–1·min^–1 to 55 ml·kg^–1·min^–1 within this temperature range.The study emphasizes that pulmonary diffusing capacity cannot be fully evaluated without information on pulmonary perfusion and O₂-uptake. In reptiles and other ectotherms diffusing capacity must be reported at specified body temperature.     

Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects

The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen uptake (V˙O_{2 max} ) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM). Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of the hand on the rim (−30°, 0° and +30°). The results indicate that paraplegic subjects reached a similar V˙O_{2 max} [1.23 (0.34) l · min⁻¹, 1.25 (0.38) l · min⁻¹, 1.22 (0.18) l · min⁻¹ for AC, TM and WE, respectively] and V˙O_{2 max} /body mass [19.7 (5.2) ml · min⁻¹ · kg⁻¹, 19.5 (6.14) ml · min⁻¹ · kg⁻¹, 19.18 (4.27) ml · min⁻¹ · kg⁻¹ for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f _{c max} during the last minute of AC (173 (17) beats · min⁻¹], TM [168 (14) beats · min⁻¹], and WE [165 (16) beats · min⁻¹], were correlated, but f _{c max} was significantly higher for AC than for TM (P<0.03). There were significant correlations between MVF and LAV (P<0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1 (71) N, at −30°, 0° and +30°, respectively]. There was no correlation between V˙O_{2 max} and LAV or MVF. The relatively low values of f _{c max} suggest that V˙O_{2 max} was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the lack of a significant correlation between V˙O_{2 max} and MVF or muscle mass was not in favour of muscle strength being the main factor limiting V˙O_{2 max} in our subjects. Accepted: 31 January 1997