Measurement of maximum oxygen consumption in Guinea fowl Numida meleagris indicates that birds and mammals display a similar diversity of aerobic scopes during running

Judgement of exercise performance in birds has been hampered by a paucity of data on maximal aerobic capacity. We measured the maximal rate of oxygen consumption (Vo2,max) in running guinea fowl Numida meleagris, a bird that has been used in several previous studies of avian running. Mean Vo2,max during level treadmill running was 97.5+/-3.7 mL O(2) kg(-1) min(-1) (mean+/-SEM, N=5). Vo2,max was on average 6% higher when the birds ran uphill compared with the value during level running (paired t-test, P=0.041, N=5). The mean basal rate of oxygen consumption (Vo2,bmr) of the same individuals was 7.9+/-0.5 mL O(2) kg(-1) min(-1). Mean factorial aerobic scope based on individually measured values of Vo2,max and Vo2,bmr was 13.2+/-0.6 (mean+/-SEM, N=5). This value was considerably lower than the factorial aerobic scope previously measured during running in Rhea americana, a large flightless ratite. The difference in factorial scope between these two running birds likely reflects the effects of body size as well as size-independent differences in the ability to deliver and use oxygen. These data confirm a previous prediction that birds have a diversity of factorial aerobic scopes similar to that exhibited by mammals.     

Inspiratory muscle training lowers the oxygen cost of voluntary hyperpnea

The purpose of this study was to determine if inspiratory muscle training (IMT) alters the oxygen cost of breathing (Vo(2RM)) during voluntary hyperpnea. Sixteen male cyclists completed 6 wk of IMT using an inspiratory load of 50% (IMT) or 15% placebo (CON) of maximal inspiratory pressure (Pi(max)). Prior to training, a maximal incremental cycle ergometer test was performed to determine Vo(2) and ventilation (V(E)) at multiple workloads. Pre- and post-training, subjects performed three separate 4-min bouts of voluntary eucapnic hyperpnea (mimic), matching V(E) that occurred at 50, 75, and 100% of Vo(2 max). Pi(max) was significantly increased (P < 0.05) by 22.5 ± 8.7% from pre- to post-IMT and remained unchanged in the CON group. The Vo(2RM) required during the mimic trial corresponded to 5.1 ± 2.5, 5.7 ± 1.4, and 11.7% ± 2.5% of the total Vo(2) (Vo(2T)) at ventilatory workloads equivalent to 50, 75, and 100% of Vo(2 max), respectively. Following IMT, the Vo(2RM) requirement significantly decreased (P < 0.05) by 1.5% (4.2 ± 1.4% of Vo(2T)) at 75% Vo(2 max) and 3.4% (8.1 ± 3.5% of Vo(2T)) at 100% Vo(2 max). No significant changes were shown in the CON group. IMT significantly reduced the O(2) cost of voluntary hyperpnea, which suggests that a reduction in the O(2) requirement of the respiratory muscles following a period of IMT may facilitate increased O(2) availability to the active muscles during exercise. These data suggest that IMT may reduce the O(2) cost of ventilation during exercise, providing an insight into mechanism(s) underpinning the reported improvements in whole body endurance performance; however, this awaits further investigation.     

Relation of heart rate to percent VO2 peak during submaximal exercise in the heat.

We tested the hypothesis that elevation in heart rate (HR) during submaximal exercise in the heat is related, in part, to increased percentage of maximal O(2) uptake (%Vo(2 max)) utilized due to reduced maximal O(2) uptake (Vo(2 max)) measured after exercise under the same thermal conditions. Peak O(2) uptake (Vo(2 peak)), O(2) uptake, and HR during submaximal exercise were measured in 22 male and female runners under four environmental conditions designed to manipulate HR during submaximal exercise and Vo(2 peak). The conditions involved walking for 20 min at approximately 33% of control Vo(2 max) in 25, 35, 40, and 45 degrees C followed immediately by measurement of Vo(2 peak) in the same thermal environment. Vo(2 peak) decreased progressively (3.77 +/- 0.19, 3.61 +/- 0.18, 3.44 +/- 0.17, and 3.13 +/- 0.16 l/min) and HR at the end of the submaximal exercise increased progressively (107 +/- 2, 112 +/- 2, 120 +/- 2, and 137 +/- 2 beats/min) with increasing ambient temperature (T(a)). HR and %Vo(2 peak) increased in an identical fashion with increasing T(a). We conclude that elevation in HR during submaximal exercise in the heat is related, in part, to the increase in %Vo(2 peak) utilized, which is caused by reduced Vo(2 peak) measured during exercise in the heat. At high T(a), the dissociation of HR from %Vo(2 peak) measured after sustained submaximal exercise is less than if Vo(2 max) is assumed to be unchanged during exercise in the heat.     

The respiratory system in varanid lizards: determinants of O(2) transfer

Varanids in general exhibit greater aerobic capacities than other lizards. In a similar approach to the extensive investigations undertaken in mammals, the respiratory system in varanids is examined in terms of oxygen transfer from the air to the blood during rest and sustained locomotory activity. The parameters controlling the transfer of O(2) through the various steps of the respiratory system are appropriate to meet the maximum demands for oxygen with one possible exception, circulatory convection. Ventilatory convection is maintained during maximal aerobic locomotion ensuring adequate pulmonary ventilation and the protection of alveolar P(O(2)). Little evidence exists to indicate a mechanically imposed constraint to breathe and the possibility of a gular pump acting to assist ventilation, as a general feature of varanids remains to be determined. Alterations in the relative contributions of the ventilation-perfusion ratio, pulmonary diffusion, diffusion equilibrium and right-left shunts preserved the alveolar-arterial P(O(2)) difference, ensuring that arterial oxygenation was maintained. In those species where increases in cardiac output were limited, maximum O(2) transfer was achieved through increased extraction of oxygen at the tissues. Overall, the interrelationship of adjacent steps in the respiratory system ensures that one step cannot become limiting. Compensatory changes occur in various parameters to offset those parameters that are 'limited'. The high aerobic activity of varanid lizards would not be achievable without a compensated circulatory convection.     

Factorial aerobic scope is independent of temperature and primarily modulated by heart rate in exercising Murray cod (Maccullochella peelii peelii)

Several previous reports, often from studies utilising heavily instrumented animals, have indicated that for teleosts, the increase in cardiac output (Vb) during exercise is mainly the result of an increase in cardiac stroke volume (V(S)) rather than in heart rate (fH). More recently, this contention has been questioned following studies on animals carrying less instrumentation, though the debate continues. In an attempt to shed more light on the situation, we examined the heart rates and oxygen consumption rates (Mo2; normalised to a mass of 1 kg, given as Mo2kg) of six Murray cod (Maccullochella peelii peelii; mean mass+/-SE = 1.81+/-0.14 kg) equipped with implanted fH and body temperature data loggers. Data were determined during exposure to varying temperatures and swimming speeds to encompass the majority of the biological scope of this species. An increase in body temperature (Tb) from 14 degrees C to 29 degrees C resulted in linear increases in Mo2kg (26.67-41.78 micromol min(-1) kg(-1)) and fH (22.3-60.8 beats min(-1)) during routine exercise but a decrease in the oxygen pulse (the amount of oxygen extracted per heartbeat; 1.28-0.74 micromol beat(-1) kg(-1)). During maximum exercise, the factorial increase in Mo2kg was calculated to be 3.7 at all temperatures and was the result of temperature-independent 2.2- and 1.7-fold increases in fH and oxygen pulse, respectively. The constant factorial increases in fH and oxygen pulse suggest that the cardiovascular variables of the Murray cod have temperature-independent maximum gains that contribute to maximal oxygen transport during exercise. At the expense of a larger factorial aerobic scope at an optimal temperature, as has been reported for species of salmon and trout, it is possible that the Murray cod has evolved a lower, but temperature-independent, factorial aerobic scope as an adaptation to the largely fluctuating and unpredictable thermal climate of southeastern Australia.     

Scaling the amplitudes of the circadian pattern of resting oxygen consumption, body temperature and heart rate in mammals

We questioned whether the amplitudes of the circadian pattern of body temperature (T(b)), oxygen consumption (V (O(2))) and heart rate (HR) changed systematically among species of different body weight (W). Because bodies of large mass have a greater heat capacitance than those of smaller mass, if the relative amplitude (i.e., amplitude/mean value) of metabolic rate was constant, one would expect the T(b) oscillation to decrease with the increase in the species W. We compiled data of T(b), V (O(2)) and HR from a literature survey of over 200 studies that investigated the circadian pattern of these parameters. Monotremata, Marsupials and Chiroptera, were excluded because of their characteristically low metabolic rate and T(b). The peak-trough ratios of V (O(2)) (42 species) and HR (35 species) averaged, respectively, 1.57+/-0.08, and 1.35+/-0.07, and were independent of W. The daily high values of T(b) did not change, while the daily low T(b) values slightly increased, with the species W; hence, the high-low T(b) difference (57 species) decreased with W (3.3 degrees C.W(-0.13)). However, the decrease in T(b) amplitude with W was much less than expected from physical principles, and the high-low T(b) ratio remained significantly above unity even in the largest mammals. Thus, it appears that in mammals, despite the huge differences in physical characteristics, the amplitude of the circadian pattern is a fixed (for V (O(2)) and HR), or almost fixed (for T(b)), fraction of the 24-h mean value. Presumably, the amplitudes of the oscillations are controlled parameters of physiological significance.     

Estimating the rate of oxygen consumption during submersion from the heart rate of diving animals

How animals manage their oxygen stores during diving and other breath-hold activities has been a topic of debate among physiologists for decades. Specifically, while the behavior of free-ranging diving animals suggests that metabolism during submersion must be primarily aerobic in nature, no studies have been able to determine their rate of oxygen consumption during submersion (Vo(2)d) and hence prove that this is the case. In the present study, we combine two previously used techniques and develop a new model to estimate Vo(2)d accurately and plausibly in a free-ranging animal and apply it to data for macaroni penguins (Eudyptes chrysolophus) as an example. For macaroni penguins at least, Vo(2)d can be predicted by measuring heart rate during the dive cycle and the subsequent surface interval duration. Including maximum depth of the dive improves the accuracy of these predictions. This suggests that energetically demanding locomotion events within the dive combine with the differing buoyancy and locomotion costs associated with traveling to depth to influence its cost in terms of oxygen use. This will in turn effect the duration of the dive and the duration of the subsequent recovery period. In the present study, Vo(2)d ranged from 4 to 28 ml.min(-1).kg(-1), indicating that, at least as far as aerobic metabolism was concerned, macaroni penguins were often hypometabolic, with rates of oxygen consumption usually below that for this species resting in water (25.6 ml.min(-1).kg(-1)) and occasionally lower than that while resting in air (10.3 ml.min(-1).kg(-1)).     

Changes in cardiac output during swimming and aquatic hypoxia in the air-breathing Pacific tarpon

Pacific tarpon (Megalops cyprinoides) use a modified gas bladder as an air-breathing organ (ABO). We examined changes in cardiac output (V(b)) associated with increases in air-breathing that accompany exercise and aquatic hypoxia. Juvenile (0.49 kg) and adult (1.21 kg) tarpon were allowed to recover in a swim flume at 27 degrees C after being instrumented with a Doppler flow probe around the ventral aorta to monitor V(b) and with a fibre-optic oxygen sensor in the ABO to monitor air-breathing frequency. Under normoxic conditions and in both juveniles and adults, routine air-breathing frequency was 0.03 breaths min(-1) and V(b) was about 15 mL min(-1) kg(-1). Normoxic exercise (swimming at about 1.1 body lengths s(-1)) increased air-breathing frequency by 8-fold in both groups (reaching 0.23 breaths min(-1)) and increased V(b) by 3-fold for juveniles and 2-fold for adults. Hypoxic exposure (2 kPa O2) at rest increased air-breathing frequency 19-fold (to around 0.53 breaths min(-1)) in both groups, and while V(b) again increased 3-fold in resting juvenile fish, V(b) was unchanged in resting adult fish. Exercise in hypoxia increased air-breathing frequency 35-fold (to 0.95 breaths min(-1)) in comparison with resting normoxic fish. While juvenile fish increased V(b) nearly 2-fold with exercise in hypoxia, adult fish maintained the same V(b) irrespective of exercise state and became agitated in comparison. These results imply that air-breathing during exercise and hypoxia can benefit oxygen delivery, but to differing degrees in juvenile and adult tarpon. We discuss this difference in the context of myocardial oxygen supply.     

Effects of temperature on metabolism,ventilation, and oxygen extraction in the southern brown bandicoot Isoodon obesulus (Marsupialia: Peramelidae)

The effects of ambient temperatures (T(a)) from 10 degrees to 35 degrees C on metabolism, ventilation, and oxygen extraction were examined for the southern brown bandicoot (Isoodon obesulus). Oxygen consumption (VO2) followed the pattern typical for endotherms, decreasing with increasing T(a) from 10 degrees to 25 degrees C. It did not significantly change between Ta=25 degrees and 35 degrees C (the thermoneutral zone). VO2 was approximately 2.4 times higher at Ta=10 degrees C (0.967 mL O(2) g(-1) h(-1)) compared with basal (0.410 mL O(2) g(-1) h(-1)) at Ta=30 degrees C. While the metabolic rates of the bandicoots were basal at Ta=30 degrees C, respiratory frequency (f(R)) was 24.6 breaths min(-1), tidal volume (V(T)) was 7.79 mL, minute volume (V(I)) was 191.3 mL min(-1), and oxygen extraction efficiency (EO2) was 26.8%. Increased VO2 at Ta< or =25 degrees C was associated with a large increase in V(I) due to increases in V(T) and f(R). A greater proportion of the change was due to the increase in tidal volume. EO2 was constant at approximately 26% for all T(a) up to and including 30 degrees C. At Ta=35 degrees C, EO2 decreased to 17.7%, f(R) increased to 35.6 breaths min(-1), and V(T) decreased to 7.22 mL. The metabolic and ventilatory physiology of the southern brown bandicoot are typical of an unspecialized medium-sized marsupial.     

Comparative study of field and laboratory tests for the evaluation of aerobic capacity in soccer players

The purpose of this study was to evaluate the maximal oxygen uptake (Vo(2)max) values in soccer players as assessed by field and laboratory tests. Thirty-five elite young soccer players were studied (mean age 18.1 +/- 1.0 years, training duration 8.3 +/- 1.5 years) in the middle of the playing season. All subjects performed 2 maximal field tests: the Yo-Yo endurance test (T(1)) for the estimation of Vo(2)max according to normogram values, and the Yo-Yo intermittent endurance test (T(2)) using portable telemetric ergospirometry; as well as 2 maximal exercise tests on the treadmill with continuous (T(3)) and intermittent (T(4)) protocols. The estimated Vo(2)max values of the T(1) test (56.33 ml.kg(-1).min(-1)) were 10.5%, 11.4%, and 13.3% (p < or = 0.05) lower than those of the T(2) (62.96 ml.kg(-1).min(-1)), T(3) (63.59 ml.kg(-1).min(-1)) and T(4) (64.98 ml.kg(-1).min(-1)) tests, respectively. Significant differences were also found between the intermittent exercise protocols T(1) and T(3) (p < or = 0.001) and the continuous exercise protocols T(2) and T(4) (p < or = 0.001). There was a high degree of cross correlation between the Vo(2)max values of the 3 ergospirometric tests (T(2) versus T(3), r = 0.47, p < or = 0.005; T(2) versus T(4), r = 0.59, p < or = 0.001; T(3) versus T(4) r = 0.79, p < or = 0.001). It is necessary to use ergospirometry to accurately estimate aerobic capacity in soccer players. Nevertheless, the Yo-Yo field tests should be used by coaches because they are easy and helpful tools in the training program setting and for player follow-up during the playing season.     

Greater rate of decline in maximal aerobic capacity with age in endurance-trained than in sedentary men.

To determine the relation between habitual endurance exercise status and the age-associated decline in maximal aerobic capacity [i.e., maximal O(2) consumption (Vo(2 max))] in men, we performed a well-controlled cross-sectional laboratory study on 153 healthy men aged 20-75 yr: 64 sedentary and 89 endurance trained. Vo(2 max) (ml. kg(-1). min(-1)), measured by maximal treadmill exercise, was inversely related to age in the endurance-trained (r = -0.80) and sedentary (r = -0.74) men but was higher in the endurance-trained men at any age. The rate of decline in Vo(2 max) with age (ml. kg(-1). min(-1)) was greater (P < 0.001) in the endurance-trained than in the sedentary men. Whereas the relative rate of decline in Vo(2 max) (percent decrease per decade from baseline levels in young adulthood) was similar in the two groups, the absolute rate of decline in Vo(2 max) was -5.4 and -3.9 ml. kg(-1). min(-). decade(-1) in the endurance-trained and sedentary men, respectively. Vo(2 max) declined linearly across the age range in the sedentary men but was maintained in the endurance-trained men until approximately 50 yr of age. The accelerated decline in Vo(2 max) after 50 yr of age in the endurance-trained men was related to a decline in training volume (r = 0.46, P < 0.0001) and was associated with an increase in 10-km running time (r = -0.84, P < 0.0001). We conclude that the rate of decline in maximal aerobic capacity during middle and older age is greater in endurance-trained men than in their sedentary peers and is associated with a marked decline in O(2) pulse.     

The relationship of the heart rate deflection point to the ventilatory threshold in trained cyclists

The purpose of this study was to assess the relationship of the heart rate deflection point (HRDP) to the ventilatory threshold (VT) in trained cyclists. Twenty-one endurance-trained cyclists (mean +/- SD: Vo(2)max = 67.6 +/- 4.7 ml x kg x min(-1)) completed a maximal cycle ergometer test of volitional fatigue using a ramped protocol. Ventilatory variables (Ve, Vo(2), Vco(2)) and power were measured online with averages reported every 20 seconds. Heart rate (HR) was recorded every 20 seconds using a Polar monitor. VT was calculated using the excess CO(2) elimination curve. The first derivative of a logistic growth curve fit to the HR-power data produced the HRDP. No significant differences (p > 0.01) existed between HR values at HRDP (171.7 +/- 9.6 b x min(-1)) and VT (169.8 +/- 9.9 b x min(-1)) or between Vo(2) values at HRDP (53.6 +/- 4.2 ml x kg x min(-1)) and VT (52.2 +/- 4.8 ml x kg x min(-1)). But power values at HRDP (318.7 +/- 30.7 W) were significantly different (p < 0.01) from those at VT (334.8 +/- 36.7 W). There were significant relationships between HRDP and VT for the physiological variables of HR (r = 0.92, p < 0.001), Vo(2) (r = 0.72, p < 0.001), and power (r = 0.77, p < 0.001). These findings indicate that HR and Vo(2) at HRDP are not significantly different from the values at VT in trained cyclists. HR values derived from HRDP may be used to set parameters for training intensity. Variability in the speed/power-HRDP relationship across detrained/trained states may be used to evaluate training programs.     

Metabolism and thermoregulation during fasting in king penguins, Aptenodytes patagonicus, in air and water

We measured oxygen consumption rate (Vo(2)) and body temperatures in 10 king penguins in air and water. Vo(2) was measured during rest and at submaximal and maximal exercise before (fed) and after (fasted) an average fasting duration of 14.4 +/- 2.3 days (mean +/- 1 SD, range 10-19 days) in air and water. Concurrently, we measured subcutaneous temperature and temperature of the upper (heart and liver), middle (stomach) and lower (intestine) abdomen. The mean body mass (M(b)) was 13.8 +/- 1.2 kg in fed and 11.0 +/- 0.6 kg in fasted birds. After fasting, resting Vo(2) was 93% higher in water than in air (air: 86.9 +/- 8.8 ml/min; water: 167.3 +/- 36.7 ml/min, P < 0.01), while there was no difference in resting Vo(2) between air and water in fed animals (air: 117.1 +/- 20.0 ml O(2)/min; water: 114.8 +/- 32.7 ml O(2)/min, P > 0.6). In air, Vo(2) decreased with M(b), while it increased with M(b) in water. Body temperature did not change with fasting in air, whereas in water, there were complex changes in the peripheral body temperatures. These latter changes may, therefore, be indicative of a loss in body insulation and of variations in peripheral perfusion. Four animals were given a single meal after fasting and the temperature changes were partly reversed 24 h after refeeding in all body regions except the subcutaneous, indicating a rapid reversal to a prefasting state where body heat loss is minimal. The data emphasize the importance in considering nutritional status when studying king penguins and that the fasting-related physiological changes diverge in air and water.     

Breath-by-breath assessment of alveolar gas stores and exchange.

The volume of O(2) exchanged at the mouth during a breath (Vo(2,m)) is equal to that taken up by pulmonary capillaries (Vo(2,A)) only if lung O(2) stores are constant. The latter change if either end-expiratory lung volume (EELV), or alveolar O(2) fraction (Fa(O(2))) change. Measuring this requires breath-by-breath (BbB) measurement of absolute EELV, for which we used optoelectronic plethysmography combined with measurement of O(2) fraction at the mouth to measure Vo(2,A) = Vo(2,m) - (DeltaEELV x Fa(O(2)) + EELV x DeltaFa(O(2))), and divided by respiratory cycle time to obtain BbB O(2) consumption (Vo(2)) in seven healthy men during incremental exercise and recovery. To synchronize O(2) and volume signals, we measured gas transit time from mouthpiece to O(2) meter and compared Vo(2) measured during steady-state exercise by using expired gas collection with the mean BbB measurement over the same time period. In one subject, we adjusted the instrumental response time by 20-ms increments to maximize the agreement between the two Vo(2) measurements. We then applied the same total time delay (transit time plus instrumental delay = 660 ms) to all other subjects. The comparison of pooled data from all subjects revealed r(2) = 0.990, percent error = 0.039 +/- 1.61 SE, and slope = 1.02 +/- 0.015 (SE). During recovery, increases in EELV introduced systematic errors in Vo(2) if measured without taking DeltaEELV x Ca(O(2))+EELV x DeltaFa(O(2)) into account. We conclude that optoelectronic plethysmography can be used to measure BbB Vo(2) accurately when studying BbB gas exchange in conditions when EELV changes, as during on- and off-transients.     

Similar level of impairment in exercise performance and oxygen uptake kinetics in middle-aged men and women with type 2 diabetes

The present study tested the hypothesis that the magnitude of the type 2 diabetes-induced impairments in peak oxygen uptake (Vo(2)) and Vo(2) kinetics would be greater in females than males in middle-aged participants. Thirty-two individuals with type 2 diabetes (16 male, 16 female), and 32 age- and body mass index (BMI)-matched healthy individuals (16 male, 16 female) were recruited. Initially, the ventilatory threshold (VT) and peak Vo(2) were determined. On a separate day, subjects completed four 6-min bouts of constant-load cycling at 80% VT for the determination of Vo(2) kinetics using standard procedures. Cardiac output (CO) (inert gas rebreathing) was recorded at rest, 30, and 240 s during two additional bouts. Peak Vo(2) (ml·kg(-1)·min(-1)) was significantly reduced in men and women with type 2 diabetes compared with their respective nondiabetic counterparts (men, 27.8 ± 4.4 vs. 31.1 ± 6.2 ml·kg(-1)·min(-1); women, 19.4 ± 4.1 vs. 21.4 ± 2.9 ml·kg(-1)·min(-1)). The time constant (s) of phase 2 (τ(2)) and mean response time (s) of the Vo(2) response (MRT) were slowed in women with type 2 diabetes compared with healthy women (τ(2), 43.3 ± 9.8 vs. 33.6 ± 10.0 s; MRT, 51.7 ± 9.4 vs. 43.5 ± 11.4s) and in men with type 2 diabetes compared with nondiabetic men (τ(2), 43.8 ± 12.0 vs. 35.3 ± 9.5 s; MRT, 57.6 ± 8.3 vs. 47.3 ± 9.3 s). The magnitude of these impairments was not different between males and females. The steady-state CO responses or the dynamic responses of CO were not affected by type 2 diabetes among men or women. The results suggest that the type 2 diabetes-induced impairments in peak Vo(2) and Vo(2) kinetics are not affected by sex in middle aged participants.     

Pharmacokinetics of flumequine and in vitro activity against bacterial pathogens of gilthead sea bream Sparus aurata

The present study investigated the kinetic profile of flumequine (FLU) in gilthead sea bream Sparus aurata (170 g) held at 19 degrees C and evaluated its in vitro efficacy against important bacterial diseases in Mediterranean mariculture. Following a single intravascular injection (10 mg kg(-1) fish), the distribution half-life (t1/2alpha) and the half-life of the terminal phase of elimination (t1/2gamma) of the drug were 0.2 and 30 h respectively. Tissue penetration of FLU was low, since both the apparent distribution volume of the drug at steady-state (Vd(SS)) and the apparent volume of the central compartment (Vc) were small (0.57 and 0.15 l kg(-1)). The mean residence time (MRT) was short (11 h) and the total clearance (CL(T)) of the drug was slow (0.05 l kg(-1) h(-1)). Following oral administration (20 mg kg(-1)), the bioavailability (F %) of FLU was 29% and the maximum plasma concentration was 1.7 microg ml(-1). The minimum inhibitory concentration (MIC) of the drug in distilled water supplemented with 2% NaCl against Vibrio anguillarum Serotype 1b, Photobacterium damsela ssp. piscicida, V. alginolyticus, V. damsela and V. fluvialis was 0.15, 0.3, 1.2, 0.019 and 0.15 microg ml(-1) respectively. The addition however of 10 mM Ca2+ and 55 mM Mg2+ to the medium resulted in an 8- to >120-fold reduction in FLU activity. The results indicate that FLU has an adequate kinetic profile in gilthead sea bream and that marine cations induce a significant impact on the activity of FLU, rendering its use against bacterial pathogens questionable.     

Non-standard O(2) consumption-temperature curves during rest and isometric exercise in human skeletal muscle

The present work was aimed at measuring intramuscular oxygen consumption (O(2)) as a function of temperature (T), in human forearm, during rest and aerobic isometric exercise (4% of the maximal voluntary contraction, MVC). Based upon results from in vitro experiments performed on isolated mitochondria of animal species, it was hypothesised that, during isometric exercise, the O(2)-T curve should display a maximum for some 'optimal' T. Intramuscular T and measurements were performed using a combined deep body temperature/near infrared probe during muscle cooling. At rest, O(2) increased non-linearly and monotonically as a function of T (n=8). O(2) increased approximately 2 times when going from 26 to 36 degrees C. A log(O(2))-T plot or a log(O(2))-1/T did not linearise the data. During isometric contraction, O(2) values at 26.8+/-0.6, 28.6+/-0.9, 31.9+/-0.9 and 35.9+/-0.9 degrees C were 3.04+/-1.26, 7.60+/-1.64, 4.43+/-1.95, and 6.64+/-1.37 micromol 100 g(-1) min(-1), respectively (n=6). The O(2) value at 28.6 degrees C was significantly higher (P<0.05) than that at 26.8 and 31.9 degrees C. The 'sudden' O(2) change at 28.6 degrees C is compatible with the phenomenon observed at the mitochondrial level.     

A novel cardiopulmonary exercise test protocol and criterion to determine maximal oxygen uptake in chronic heart failure

Cardiopulmonary exercise testing for peak oxygen uptake (Vo(2peak)) can evaluate prognosis in chronic heart failure (CHF) patients, with the peak respiratory exchange ratio (RER(peak)) commonly used to confirm maximal effort and maximal oxygen uptake (Vo(2max)). We determined the precision of RER(peak) in confirming Vo(2max), and whether a novel ramp-incremental (RI) step-exercise (SE) (RISE) test could better determine Vo(2max) in CHF. Male CHF patients (n = 24; NYHA class I-III) performed a symptom-limited RISE-95 cycle ergometer test in the format: RI (4-18 W/min; ～10 min); 5 min recovery (10 W); SE (95% peak RI work rate). Patients (n = 18) then performed RISE-95 tests using slow (3-8 W/min; ～15 min) and fast (10-30 W/min; ～6 min) ramp rates. Pulmonary gas exchange was measured breath-by-breath. Vo(2peak) was compared within patients by unpaired t-test of the highest 12 breaths during RI and SE phases to confirm Vo(2max) and its 95% confidence limits (CI(95)). RER(peak) was significantly influenced by ramp rate (fast, medium, slow: 1.21 ± 0.1 vs. 1.15 ± 0.1 vs. 1.09 ± 0.1; P = 0.001), unlike Vo(2peak) (mean n = 18; 14.4 ± 2.6 ml·kg(-1)·min(-1); P = 0.476). Group Vo(2peak) was similar between RI and SE (n = 24; 14.5 ± 3.0 vs. 14.7 ± 3.1 ml·kg(-1)·min(-1); P = 0.407); however, within-subject comparisons confirmed Vo(2max) in only 14 of 24 patients (CI(95) for Vo(2max) estimation averaged 1.4 ± 0.8 ml·kg(-1)·min(-1)). The RER(peak) in CHF was significantly influenced by ramp rate, suggesting its use to determine maximal effort and Vo(2max) be abandoned. In contrast, the RISE-95 test had high precision for Vo(2max) confirmation with patient-specific CI(95) (without secondary criteria), and showed that Vo(2max) is commonly underestimated in CHF. The RISE-95 test was well tolerated by CHF patients, supporting its use for Vo(2max) confirmation.     

Oxygen limitation of thermal tolerance in cod, Gadus morhua L., studied by magnetic resonance imaging and on-line venous oxygen monitoring

The hypothesis of an oxygen-limited thermal tolerance due to restrictions in cardiovascular performance at extreme temperatures was tested in Atlantic cod, Gadus morhua (North Sea). Heart rate, changes in arterial and venous blood flow, and venous oxygen tensions were determined during an acute temperature change to define pejus ("getting worse") temperatures that border the thermal optimum range. An exponential increase in heart rate occurred between 2 and 16 degrees C (Q(10) = 2.38 +/- 0.35). Thermal sensitivity was reduced beyond 16 degrees C when cardiac arrhythmia became visible. Flow-weighted magnetic resonance imaging (MRI) measurements of temperature-dependent blood flow revealed no exponential but a hyperbolic increase of blood flow with a moderate linear increase at temperatures >4 degrees C. Therefore, temperature-dependent heart rate increments are not mirrored by similar increments in blood flow. Venous Po(2) (Pv(O(2))), which reflects the quality of oxygen supply to the heart of cod (no coronary circulation present), followed an inverse U-shaped curve with highest Pv(O(2)) levels at 5.0 +/- 0.2 degrees C. Thermal limitation of circulatory performance in cod set in below 2 degrees C and beyond 7 degrees C, respectively, characterized by decreased Pv(O(2)). Further warming led to a sharp drop in Pv(O(2)) beyond 16.1 +/- 1.2 degrees C in accordance with the onset of cardiac arrhythmia and, likely, the critical temperature. In conclusion, progressive cooling or warming brings cod from a temperature range of optimum cardiac performance into a pejus range, when aerobic scope falls before critical temperatures are reached. These patterns might cause a shift in the geographical distribution of cod with global warming.     

GABA(A) and GABA(B) receptors differentially modulate volume and frequency in ventilatory compensation in obese Zucker rats.

The aim of this study was to investigate whether GABA(A) and/or GABA(B) receptor-mediated mechanisms contribute to the impaired ventilatory response and reduced maximal aerobic exercise capacity in obese Zucker rats. Ten lean and 10 obese Zucker rats were studied at 12 wk of age. Minute ventilation (Ve), tidal volume (Vt), and breathing frequency (f) during room air breathing and in response to 10 min of hypercapnia (8% CO(2)) and 30 min of hypoxia (10% O(2)) were measured by the barometric method, and peak oxygen consumption (Vo(2 peak)) was measured by an enclosed metabolic treadmill following the randomized blinded subcutaneous administration of equal volumes of DMSO (vehicle), bicuculline (selective GABA(A) receptor antagonist, 1 mg/kg), and phaclofen (selective GABA(B) receptor antagonist, 1 mg/kg). Administration of bicuculline and phaclofen to lean animals had no effect on Ve and Vo(2 peak). Similarly, phaclofen failed to alter Ve and Vo(2 peak) in obese rats, although it did significantly increase f after 5-20 min of hypoxia. In contrast, bicuculline increased Ve and Vt relative to DMSO during room air breathing and after 10-30 min of hypoxic exposure in obese rats, but it did not increase Ve at 5 min of hypoxemia. Bicuculline increased Vo(2 peak) relative to DMSO in obese Zucker rats. We conclude that endogenous GABA acting on GABA(A) receptors can modulate Ve and Vo(2 peak) in obese but not in lean Zucker rats, whereas endogenous GABA acting on GABA(B) receptors modulates f during hypoxia (5-20 min) in obese rats in a very different manner from that when acting on GABA(A) receptors.