Energy requirements of Adélie penguin (Pygoscelis adeliae) chicks

Summary The energy requirements of Adélie penguin (Pygoscelis adeliae) chicks were analysed with respect to body mass (W, 0.145–3.35 kg, n=36) and various forms of activity (lying, standing, minor activity, locomotion, walking on a treadmill). Direct respirometry was used to measure O₂ consumption ( ) and CO₂ production. Heart rate (HR, bpm) was recorded from the ECG obtained by both externally attached electrodes and implantable HR-transmitters. The parameters measured were not affected by hand-rearing of the chicks or by implanting transmitters. HR measured in the laboratory and in the field were comparable. Oxygen uptake ranged from in lying chicks to at maximal activity, RQ=0.76. Metabolic rate in small wild chicks (0.14–0.38 kg) was not affected by time of day, nor was their feeding frequency in the colony (Dec 20–21). Regressions of HR on were highly significant (p< 0.0001) in transmitter implanted chicks (n=4), and two relationships are proposed for the pooled data, one for minor activities ( ), and one for walking ( ). Oxygen consumption, mass of the chick (2–3 kg), and duration of walking (T, s) were related as , whereas mass-specific O₂ consumption was related to walking speed (S, m·s^-1) as .Abbreviations bpm beats per minute - D distance walked (m) - ECG electrocardiogram - HR heart rate (bpm) - ns number of steps - RQ respiratory quotient - S walking speed (m·s^-1) - T time walked (s) - W body mass (kg)     

Thermoregulation,gas exchange,and ventilation in Adelie penguins (Pygoscelis adeliae)

Summary Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (T _a) in their natural habitat. We examined body temperature (T _b), oxygen consumption ( ), carbon dioxide production ( ), evaporative water loss ( ), and ventilation atT _a from –20 to 30 °C. Body temperature did not change significantly between –20 and 20°C (meanT _b=39.3°C).T _b increased slightly to 40.1 °C atT _a=30°C. Both and were constant and minimal atT _a between –10 and 20°C, with only minor increases at –20 and 30°C. The minimal of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g·min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at allT _a. Values of were low at lowT _a, but increased to 0.21 g/min at 30°C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between –20 and 30°C. Evaporative heat loss (EHL) comprised about 5% of MHP at lowT _a, rising to 47% of MHP atT _a=30°C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [I], and oxygen extraction [ ]) were fairly stable between –20 and 10°C (VT did not change significantly over the entireT _a range). However, there was considerable inter- and intra-individual variation in ventilation patterns. AtT _a=20–30°C,f increased 7-fold over the minimal value of 7.6 breaths/min, and I showed a similar change. fell from 28–35% at lowT _a to 6% atT _a=30°C.Abbreviations C thermal conductance - EHL evaporative heat loss - oxygen extraction - f respiratory frequency - MHP metabolic heat production - evaporative water loss - LCT lower critical temperature - RE respiratory exchange ratio - T _a ambient temperature - T _b body temperature - rate of oxygen consumption - rate of carbon dioxide production - I inspiratory minute volume - VT tidal volume     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

Adaptive variations in heat production within Gerbils (genus Gerbillus) from different habitats

Summary Species of the genus Gerbillus are very common among the rodent fauna inhabiting arid zones and dune habitats in the palaearctic region. In Israel G. nanus is distributed in extreme arid areas, while G. allenbyi is common in coastal plain dune habitats, of mesic and semi-arid areas. Therefore, their distribution pattern is considered allopatric.Heat production, estimated by the oxygen consumption (Vo2), and body temperature (T _b) at various ambient temperatures were measured in both gerbils. The thermoneutral zone for G. allenbyi is between T _a=28–35° C ( T _b=36.3–38.3° C) and for G. nanus is at T _a=33±1° C ( , T _b=38.8° C). The values at thermoneutrality are 75.7% and 50.6% respectively of the calculated values for rodents with a mean body weight of 35.3 g and 28.4 g.Nonshivering thermogenesis (NST) was measured in both species as the maximal response to an injection of noradrenaline (2.0 mg/Kg s.c.). NST magnitude was the same for both species.The results show that both gerbils are adapted to arid environments. The difference in the thermoneutral zones of the two species is discussed in terms of its adaptive nature.     

Growth yields and saturation constant of Desulfovibrio vulgaris in chemostat culture

Desulfovibrio vulgaris (strain Marburg) was grown on H₂ and sulfate as sole energy source in a chemostat limited by the sulfate supply. The biomass concentration and the sulfate concentration in the culture were determined as a function of the dilution rate. From the data a K _S (saturation constant) for sulfate of 10 M, a _max of 0.23 h^–1, and a of 13 g/mol were calculated. The organism was also grown in chemostat culture on H₂ and sulfite, H₂ and thiosulfate, and pyruvate (without sulfate). was found to be 35 g/mol, 36 g/mol, and Y _pyr ^max 10 g/mol. The growth yields are discussed with respect to ATP gains in dissimilatory sulfate reduction.     

Water relations of buried eggs of mound building birds

Summary Eggs of the brush turkey (BT) and mallee fowl (MF) are incubated in mounds of soil and plant litter. Humidity in BT mounds is always near saturation (>99% RH), but in MF mounds it drops to lower values in summer (x=77% RH). Despite these high humidities, the eggs lose an average of 9.5% (BT) and 12.0% (MF) of their initial mass by evaporation before hatching. The rate of evaporation increases during incubation several-fold due to large changes in water vapor conductance of the shell and embryonic heat production. Values of in fully incubated eggs in mound material are about 3–6 times higher than values obtained from unincubated eggs in desiccators. This effect depends on two factors: (1) increases with ambient humidity, especially above 80% RH, possibly because the effective site of evaporation moves out along the walls of the pores in the eggshell. (2) Structural changes of the pores due to calcium absorption by the embryo directly increase . The first factor is most important in BT eggs and the second is dominant in MF eggs. Production of metabolic heat by the embryo increases the vapor pressure difference across the shell and further increases , especially in mounds of high humidity. The changes in pore structure are adaptive because they produce high conductances to respiratory gases and cause normal gas tensions within the egg at the end of development, yet is low enough in early development to prevent excessive water loss. Water not lost by evaporation or taken up by the embryo is stored and released during hatching. A small amount of mass is lost during incubation by respiratory gas exchange.Abbreviations BT brush turkey - MF mallee fowl - RH relative humidity     

A comparative study of the mechanism of Na+ and Cl? excretion by the gill ofMugil capito andFundulus heteroclitus: Effects of Stress

Summary In seawater (SW)-adaptedMugil andFundulus, gill effluxes of Na⁺ and of Cl^– and the simultaneously recorded transgill potential (P.D.) differ according to whether they are measured in stressed or rested animals.In rested animals of the two species, transfer to Ringer's solution considerably reduces the P.D. but not . InFundulus, is also decreased. Transfer of the two species from SW to fresh water (FW) reduces and by 75 to 85% and leads to a large inversion of P.D. When K⁺ is added to FW, a gill depolarization occurs, as well as a large increase of and .These results suggest that: 1) the P.D. originates primarily from the diffusion of cations, the gill permeability to Na⁺ ( ) being greater than that to Cl^– ( ), 2) a Cl^–/Cl^– exchange independent of P.D. is associated with the Cl^– pump; 3) Cl^– pump activity is linked to Na⁺/K⁺ exchange which in turn is associated to a Na⁺/Na⁺ exchange diffusion mechanism.In stressed individuals of the two species, the P.D. in SW, as well as the P.D. changes observed during transfer experiments, are considerably reduced. The decrease of and observed after transfer from SW to FW are also minimised. Changes are smaller inFundulus. The decrease of P.D. characterizing stressed animals may be at least in part due to a 3 to 4 fold increase of which becomes equal to in both species.As a result of stress, the K⁺-activated Na⁺ and Cl^– excretion mechanisms are totally inhibited inFundulus and partially so inMugil.Stress response seems more intense inFundulus and recovery from stress faster inMugil.     

Carbonic anhydrase activity in the blood and the gills of rainbow trout during long-term hypercapnia in hard,bicarbonate-rich freshwater

Summary Carbonic anhydrase (CA) activities in gills and venous blood, acid-base balance, and haematological variables were studied during environmental hypercapnia in rainbow trout (Salmo gairdneri). Batches of 8–10 fish were exposed to about 3 or 13 mmHg in flow-through tests of various duration from 4 h to 80 days.After initial acidosis, blood pH rose above pre-experimental values. At 3 mmHg it became normal again within 21 days, while at 13 mmHg the overshoot lasted for 80 days. In fish acclimated for 3 weeks or more to 13 mmHg , blood HCO ₃ ^– increased four to five times while plasma Cl^– levels were lower and K⁺ higher. Na⁺ levels did not show any consistent trend associated with exposure to hypercapnia. After an initial acidaemia, Hct, Hb, and RBC remained relatively constant.Patterns of change in CA activity differed between gills and erythrocytes. Initially, blood CA decreased at both levels. It then began rising after about 3 weeks and tended to reach pre-experimental values by 80 day's hypercapnia. At 13 mmHg , gill CA increased to twice the pre-experimental level. Compared with blood CA, gill CA appeared to be more specifically involved in fish acclimation to hypercapnia, which demands an increase in blood bicarbonate to provide a sufficient buffering capacity. Increased CA indicates that the gill enzyme may play a more important role than blood CA in acid-base regulation in fish during hypercapnia.Abbreviations CA carbonic anhydrase - Hb haemoglobin - Hct haematocrit value - RBC red blood cells     

Physiological mechanisms for underwater endurance: Canada goose (Branta canadensis) versus Pekin duck (Anas platyrhynchos)

Maximum submergence time of Canada geese was 18% of that of similarly sized Pekin ducks. Due to a smaller respiratory system volume the oxygen store of Canada geese was 82% of that of Pekin ducks, accounting for approximately 33% of the difference in underwater survival times. The respiratory properties and volume of the blood were similar in both species. Both species utilised approximately 79% of the respiratory oxygen store and 90% of the blood oxygen store. Therefore, most of the species difference in survival times was due to a less effective oxygen-conserving cardiovascular response (bradycardia, peripheral vasoconstriction) in Canada geese. Duck cardiac chronotropic sensitivity to hypoxia during submergence was twice that observed in geese. Furthermore, a lower hypoxic ventilatory response was observed in geese than in ducks. Density of monoamine varicosities in hindlimb artery walls was lower in geese than ducks. However, electrical stimulation of the hindlimb muscles did not cause ascending vasodilation during submergence in either species, perhaps due to higher levels of catecholamines in submerged geese. We conclude that the major difference between species is higher oxygen chemosensitivity in ducks which effects a much more rapid and efficacious oxygen-conserving response during forced submergence.Abbreviations ATPS · BTPS · STPD CNS central nervous system - EEG electroencephalogram - ECG electrocardiogram - EDTA ethylenediaminetetra-acetic acid - HPLC high performance liquid chromatography - fractional oxygen concentration of inspired air - pre-immersion fractional concentration of oxygen in the respiratory system - pre-emersion fractional concentration of oxygen in the respiratory system - [Hb] haemoglobin concentration - Hct haematocrit - HR heart rate - M _B body mass - M _b brain mass - M _h heart mass - partial pressure of carbon dioxide in arterial blood - partial pressure of oxygen in arterial blood - SPG sucrose-potassium phosphate-glyoxylic acid - t _d maximum underwater survival time - respiratory minute volume - V _pl plasma volume - V _rs respiratory system volume - accessible respiratory system oxygen store - total non-myoglobin-bound oxygen store - V _tb blood volume - blood oxygen store     

Effects of variation in total and regional shell conductance on air cell gas tensions and regional gas exchange in chicken eggs

Summary Gas conductance of the shell, rates of O₂ consumption, CO₂ production and air cell gas tensions were measured in pre-internal pipping, 19 day-old chicken eggs that were selected for a wide range in shell conductance. Regional conductance was measured in eggs with partially waxed shells.Surface-specific shell conductance was not uniform over the egg; it was over 3-fold higher at the poles than at the equator. Conductance was about 59% higher over the air cell than over the chorioallantoic part of the egg. Surface-specific perfusion was 12% higher in the air cell. Therefore the in the air cell was higher, and the lower, than values calculated for the whole egg. The mean difference in between the air cell and the chorioallantoic part of the egg was 14.8 Torr, and that of , was 7.0 Torr. These differences were somewhat dependent on total conductance. Respiratory gas exchange ratio ( ) was higher in the air cell (R=0.82) and lower in the chorioallantoic region (R=0.67) than for the whole egg (R=0.70). Air cell R increased slightly in eggs of higher total conductance.Mismatching of regional shell conductance and chorioallantoic perfusion contributes to a functional venous shunt that is partly responsible for nonequilibrium between the air cell and the blood in the chorioallantoic veins.Symbols and abbreviations D gas diffusity - F _A fractional surface area - F _G fractional conductance - G conductance - G _diff diffusion conductance - G _perf perfusion conductance - PA average gas pressure (O₂ or CO₂) - Pac gas pressure in air cell - PE gas pressure in respiratory chamber - Pca gas pressure over chorioallantois - perfusion     

Water economy in bird nests

Summary Nest humidity ( ) under an incubating bantam hen was measured at ambient ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest and ambient were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest increased linearly with ambient in a way predictable on the assumption that the water vapour conductance ( ) of brood patch skin, plumage and eggs were constant and independent of ambient . Nest was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest at varying ambient . Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations water vapur pressure - water vapur conductance - water flux     

Effects of long scotophase and cold acclimation on heat production in two diurnal rodents

Summary Heat production of two diurnal rodents,Rhabdomys pumilio andLemniscomys griselda was measured in long scotophase-LS (8L: 16D; 25°C) acclimated and long scotophase and cold — LSAC (8L: 16D; 6°C) acclimated animals and compared to a control group (12L: 12D; 25°C).LS increased in both species. Further acclimation of LSAC increased inR. pumilio and decreased inL. griselda. LS increased body temperature (T _b) inL. griselda only. LS increased overall thermal conductance in both species. LSAC caused a further increase in this parameter inR. pumilio.A singificant (P<0.001) increase in the magnitude of maximal nonshivering thermogenesis (NST) was observed in both species due to LS acclimation. LSAC did not change this maximal NST but increased its obligatory part (minimal , P<0.05, inL. griselda, andP<0.001, inR. pumilio).The results of this study show that winter acclimatization of heat production mechanisms, in both species, may be due to extension of scotophase.Abbreviations LS long scotophase - LSAC long scotophase and cold - NA noradrenaline - NST nonshivering thermogenesis - RMR resting metabolic rate     

The effect of ambient temperature on the relationship between ventilation and metabolism in a small parrot (Agapornis roseicollis)

Summary Values for basal metabolism, standard tidal volume (V _T), standard minute volume ( ), and mean extraction efficiency (EO₂) in the thermal neutral zone (TNZ) inAgapornis roseicollis (1.84 ml·min^–1; 0.95 ml·br^–1, STPD; and 33.3 ml·min^–1, STPD; and 22.5%; respectively) were all very similar to values for these parameters previously measured inBolborhynchus lineola, a similarly sized, closely related species from a distinctly different habitat.Having both a lower critical temperature (T_lc) below and an upper critical temperature (T_uc) above those ofB. lineola, the TNZ ofA. roseicollis extended from 25° to at least 35°C. The thermal conductance below the TNZ ofA. roseicollis was 14% less than that ofB. lineola. Therefore, at 5°C the standard metabolic rate (SMR) of the former is 17% less than that of the latter, and at 35°C it is 20% less. At 5°CA. roseicollis has a lower EO₂ and at 35°C a higher EO₂ than that ofB. lineola. The patterns of resting energy metabolism and of ventilation ofA. roseicollis and ofB. lineola are consistent with the former species being better suited to living in a more variable thermal environment than the latter.MeanV _T has a weak positive correlation with the rate of oxygen consumption ( ) at a constant ambient temperature (T _a) but a much stronger correlation when resting increases in response to a decrease inT _a.V _t is the only ventilatory parameter which is linearly correlated toT _a from 35° to –25°C. The data suggest thatT _a may have a regulatory effect onV _T somewhat independent of or .     

Contributions of aerobic and anaerobic energy production during swimming in the bivalve molluscLimaria fragilis (family limidae)

Summary Oxygen consumption rates ( ) and a number of possible anaerobic end products were determined forLimaria fragilis at rest, and following active swimming. increased up to 8-fold (=4) during swimming. Swimming did not change the concentrations ofl-lactate, alanine or arginine phosphate in the single striated fast adductor muscle. Octopine, succinate andd-lactate were not detected in the adductor muscles of resting or active animals (<0.2 moles/g wet weight).It is concluded that the slow sustained swimming displayed byLimaria utilises predominantly aerobic mechanisms of ATP production.     

Prediction of individual oxygen uptake on-step transients from frequency responses

Power-oxygen uptake ( ) frequency responses can be used to predict responses to arbitrary exercise intensity patterns. It is still an open question for which range of exercise intensities such computed response patterns yield valid predictions. In the present study, we determined the power- frequency response of nine sports students by means of pseudo-randomised switching between 20 W and 80 W during upright and supine cycle exercise. Starting from a baseline of 20 W each subject also performed sustained step increases to 40 W, 80 W, 120 W, and 160 W in both positions. The individual step responses were then compared with the expected time-courses predicted on the basis of the individual frequency responses. The comparison showed a close agreement for the 20 W–40 W and 20 W–80 W steps in both positions. With larger step amplitudes the kinetics became increasingly slower than the predicted time course in both positions. During additional ramp tests (10 W · 30 s^–1) whole blood lactic acid concentration [1a^–]_b tended to be higher in the supine position at exercise intensities higher than 160 W. The mean power at 4 mmol · 1^–1 [la^–]_b amounted to 234 (SD 32) W and 253 (SD 44) W (P<5%) in the supine and the upright position, respectively. The maximal oxygen uptake relative to body mass was not found to be significantly different [upright, mean 57 (SD 10) ml · (min · kg)^–1;supine, mean 54 (SD 10) ml · (min · kg)]. These findings would suggest that for a range of mild exercise intensities kinetics are not appreciably influenced by the step amplitude or by cardiovascular changes associated with the upright and the supine position.     

Water pH and aluminum chemistry in the gill micro-environment of rainbow trout during acid and aluminum exposures

Summary Rainbow trout (Salmo gairdneri) were exposed to acidic soft water (pH_in4.2–6.3) in the presence (93 g·l^–1) or absence of Al. Fish were fitted with latex masks and opercular catheters to measure ventilation , pH changes at the gills, O₂ consumption , ammonia excretion , and Al extraction. During 2–3-h exposures, was generally higher in Al-exposed fish over the pH_in range 4.7–6.3. Alkalinization of expired water was about 0.3 pH units less in Al-exposed fish than in acid-only exposed fish at pH_in 4.5–5.2, an effect attributable to both increased and to buffering by Al. During 44-h exposures to pH_in 5.2 and 4.8 plus Al, increased greatly and expired water pH (pH_ex) decreased with time. There was a small increase in over 44 h at pH 4.4 plus Al, and no changes in pH_ex. In contrast, during 44-h exposures to pH 5.2, 4.8, and 4.4 in the absence of Al, such changes were much smaller or absent. During both short- and longerterm exposures, measured Al accumulation on the gills was only 5–18% of that calculated from cumulative Al extraction from the water, suggesting considerable sloughing of Al. In free-swimming trout, gill Al accumulation was greatest during exposure (2h) to Al at pH 5.2, lower at pH 4.8, and least at pH 4.4 and 4.0. Our results suggest that Al deposition occurs at the gills, causing respiratory and ionoregulatory toxicity, because the pH in the branchial micro-environment is raised above that in the acidic inspired soft water. Higher pH at fish gills may result in Al precipitation due to loss of solubility, or Al accumulation because of shifts in Al species to Al-hydroxide forms which more readily adsorb to the gills.Abbreviations pH _ex expired pH - pH _in inspired pH     

Nitrate reductase in needles,roots and trunk wood of spruce trees [Picea abies (L.) Karst.]

Summary Nitrate reductase (EC 1.6.6.2) activity (NRA), as measured by an in vivo assay, is present in needle leaves and mycorrhizal fine root tips of adult Norway spruce [Picea abies (L.) Karst.] in at least equal amounts on a fresh weight basis, in both adult and 5-year-old trees. NRA could also be demonstrated in trunk wood of deroted trees after fertilization with 5 mM , exhibiting a longitudinal profile in the trunk. Inducibility in needles can more efficiently be achieved by NO₂ (100 g·m^-3) than by 5 mM nitrate, which is effective only in root-amputated trees. A remarkably high level of needle-NRA in unfertilized trees, which are characterized by a very low level of nitrate in the xylem sap, suggests that NRA in spruce needles may in part be constitutive. Organic-N is a major nitrogen source for the needles even in root-amputated trees, indicating pronounced exchange processes between ray parenchyma and trunk xylem, which in turn are modified by the nitrogen source fed to the trunk stump. Intact trees exhibit a very similar amino acid composition of the xylem sap, regardless of whether or has been fed. The amino acid pattern of the needles is not thrown out of balance by flooding with and , which occurs in fertilized derooted trees. This indicates a distinct potential for homoeostasis of nitrogen entrance-metabolism (i.e. NRA and glutamine synthetase activity) in the needles. In the ectomycorrhiza/fine root-system (EMC), marked differences in NRA were observed depending on root-tip diameter and along the longitudinal profile of the fine roots. EMC-nitrate reductase is strongly enhanced by . Needle-NRA exhibits a circannual rhythm. An early summer maximum is followed by a December minimum. This activity pattern matches well the transitory increase of soluble nitrogen in spring and the total protein maximum in winter. In an indirect way assimilatory NRA may well contribute to nitrogen overfertilization (by consumption of NO_X) as one possible cause of the contemporary decline of spruce populations.     

Beta-adrenergic control of blood oxygen affinity in acutely hypoxia exposed rainbow trout

Summary Acute exposure of rainbow trout to hypoxic water ( =40 mmHg, 15 °C) caused a significant (P<0.01) increase in blood O₂ affinity, from the normoxicP ₅₀ value (at pH_e 7.93) of 23.2±1.1 mmHg to about 19 mmHg, within 5 min. Specimens injected with the -antagonist propranolol showed no change in bloodP ₅₀, despite a more pronounced reduction of arterial during the hypoxic exposure.The change in bloodP ₅₀ coincided with an increase in plasma catecholamines, notably noradrenaline. There was no change in the molar ratios of ATPHb₄ and GTPHb₄. The altered bloodP ₅₀, however, correlated with an alkalinization and an increased sodium concentration of the red cells. This red cell alkalinization can be explained by -adrenergic stimulation of a membrane bound Na⁺/H⁺ antiporter.Propranolol injection into normoxic resting trout caused a significant decrease in and increase in indicating -adrenergic control of gas exchange in the gills.     

A method for determining the maximal steady state of blood lactate concentration from two levels of submaximal exercise

The aim of this study was to estimate the characteristic exercise intensity _CL which produces the maximal steady state of blood lactate concentration (MLSS) from submaximal intensities of 20 min carried out on the same day and separated by 40 min. Ten fit male adults [maximal oxygen uptake _max 62 (SD 7) ml · min^–1 · kg^–1] exercisOed for two 30-min periods on a cycle ergometer at 67% (test 1.1) and 82% of _max (test 1.2) separated by 40 min. They exercised 4 days later for 30 min at 82% of _max without prior exercise (test 2). Blood lactate was collected for determination of lactic acid concentration every 5 min and heart rate and O₂ uptake were measured every 30 s. There were no significant differences at the 5th, 10th, 15th, 20th, 25th, or 30th min between , lactacidaemia, and heart rate during tests 1.2 and 2. Moreover, we compared the exercise intensities _CL which produced the MLSS obtained during tests 1.1 and 1.2 or during tests 1.1 and 2 calculated from differential values of lactic acid blood concentration ([1a^–]_b) between the 30th and the 5th min or between the 20th and the 5th min. There was no significant difference between the different values of _CL [68 (SD 9), 71 (SD 7), 73 (SD 6),71 (SD 11) % of _max (ANOVA test,P<0.05). Four subjects ran for 60 min at their _CL determined from periods performed on the same day (test 1.1 and 1.2) and the difference between the [la^–]_b at 5 min and at 20 min ( ([la^–]_b)) was computed. The [la^–]_b remained constant during exercise and ranged from 2.2 to 6.7 mmol · l^–1 [mean value equal to 3.9 (SD 1) mmol · l^–1]. These data suggest that the _CL protocol did not overestimate the exercise intensity corresponding to the maximal fractional utilization of _max at MLSS. For half of the subjects the _CL was very close to the higher stage (82% of _max where an accumulation of lactate in the blood with time was observed. It can be hypothesized that _CL was very close to the real MLSS considering the level of accuracy of [la^–]_b measurement. This study showed that exercise at only two intensities, performed at 65% and 80% of _max and separated by 40 min of complete rest, can be used to determine the intensity yielding a steady state of [la^–1]_b near the real MLSS workload value.     

Gas exchange in the incubation mounds of megapode birds

Summary The brush turkey (Alectura lathami) and mallee fowl (Leipoa ocellata) are megapode birds that incubate their eggs by burying them in mounds. Respiratory gas exchange between the buried eggs and the atmosphere occurs mainly by diffusion through about 60 cm of decomposing forest litter (brush turkey) or sand (mallee fowl).Gas fluxes in the brush turkey mound are greatly influenced by the respiration of thermophilic microorganisms which consume O₂ at rates over eight times that of all of the eggs. The respiratory exchange ratio ( ) of the microorganisms is 0.75 and theQ ₁₀ for metabolism is 2.56. Fermentation and nitrogen fixation do not occur in the mounds.If the mound becomes too wet, gas tensions near the eggs can become critical because water increases rates of microbial respiration and impedes gas diffusion. However, field mounds are relatively dry, possibly because the adult bird modifies the shape of the mound and affects the entry of rain water. At egg level in field mounds, and are about 132 and 21 Torr, respectively, in both species. Embryonic respiration decreases and increases about 5 Torr in the immediate environment of individual eggs in late development. Due to a high eggshell gas conductance, which increases during incubation, the gas tensions within the shell of late embryos ( ca. 108 Torr, ca. 47 Torr) are not far from the mean values found in species that nest above ground.