Role of the left aortic arch and blood flows in embryonic American alligator (<Emphasis Type="Italic">Alligator mississippiensis</Emphasis>)

All embryonic and fetal amniotes possess a ductus(i) arteriosus(i) that allows blood to bypass the pulmonary circulation and the non-functional lungs. The central hemodynamic of embryonic reptiles are unique, given the additional systemic aorta that allows pulmonary circulatory bypass, the left aorta (LAo). The LAo exits in the right ventricle or ‘pulmonary side’ of reptilian hearts in both embryos and adults, but its functional significance in ovo is unknown. This study investigated the role of the LAo in embryonic American alligators by surgically occluding the LAo and measuring oxygen consumption and, in addition, measured hemodynamic responses to hypoxia in embryonic alligators. We measured systemic cardiac output and primary chorioallantoic membrane (CAM) artery blood flow for normoxic and hypoxic-incubated (10% O₂) American alligator embryos (Alligator mississippiensis). Chronic blood flow (1–124 h) in the primary CAM artery for hypoxic-incubated embryos (92 ± 26 ml min⁻¹ kg⁻¹) was elevated when compared with normoxic-incubated embryos (29 ± 14 ml min⁻¹ kg⁻¹, N = 6; P = 0.039). For hypoxic-incubated embryos, acute LAo blood flow (49.6 ± 24.4 ml min⁻¹ kg⁻¹) was equivalent to the combined flow of the three systemic great vessels that arise from the left ventricle, the right aorta, common carotid and subclavian arteries (43.6 ± 21.5 ml min⁻¹ kg⁻¹, N = 5). Similarly, for normoxic-incubated embryos, LAo blood flow (27.3 ± 6.6 ml min⁻¹ kg⁻¹) did not statistically differ from the other three vessels (18.4 ± 4.9 ml min⁻¹ kg⁻¹, N = 5). This study contains the first direct test of LAo function and the first measurements of blood flow in an embryonic reptile. These data support the hypotheses that embryonic alligators utilize the LAo to divert a significant amount of right ventricular blood into the systemic circulation, and that CAM blood flow increases following chronic hypoxic conditions. However, surgical occlusion of the LAo did not affect egg [(V)\dot]_\textO2, \dot{V}_{{\text{O}}_{2}}, supporting the hypothesis that the LAo of reptiles is not critical to maintain in ovo oxygen consumption.     

Metabolic rates in an anadromous clupeid, the American shad (Alosa sapidissima)

To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s⁻¹, 13–24 °C). Metabolic rate (M_O2) was logarithmically related to swimming speed (Bl s⁻¹; r ² = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min⁻¹; r ² = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r ² = 0.41) with a Q₁₀ of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide, ranged from 2.2–6.2 mmolO₂ kg⁻¹ h⁻¹ and scaled with mass (W) such that SMR = 4.0 (±0.03)W^{0.695(±0.15)}. Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates (M_O2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among anadromous fishes that may be important to understanding the relative success of different migratory species under varying environmental conditions. Accepted: 3 March 1999     

The Antarctic notothenioid fish <Emphasis Type="Italic">Pagothenia borchgrevinki</Emphasis> is thermally flexible: acclimation changes oxygen consumption

Antarctic marine organisms are considered to have extremely limited ability to respond to environmental temperature change. However, here we show that the Antarctic notothenioid fish Pagothenia borchgrevinki is an exception to this theory. P. borchgrevinki was able to acclimate its resting metabolic rate and resting ventilation frequency after a 5°C rise in temperature. Acute exposure to 4°C resulted in an elevation in metabolic rate (57.8 ± 4.79 mg O₂ kg⁻¹ h⁻¹) and resting ventilation rate (40.38 ± 1.61 breaths min⁻¹) compared with fish at −1°C (metabolic rate 34.45 ± 3.12 mg O₂ kg⁻¹ h⁻¹; ventilation rate 29.88 ± 3.72 breaths min⁻¹). However, after a 1-month acclimation period, there was no significant difference in the metabolic rate (cold fish 29.52 ± 3.01; warm fish 31.13 ± 2.30 mg O₂ kg⁻¹ h⁻¹), or the resting ventilation rate (cold fish 28.75 ± 0.98; warm fish 34.25 ± 2.28 breaths min⁻¹) of cold and warm acclimated fish. Acclimation changes to the rate of oxygen consumption following exhaustive exercise were complex. The pattern of oxygen consumption during recovery from exhaustive exercise was not significantly different in either cold or warm acclimated fish.     

Effects of temperature on metabolic rate and lower dissolved oxygen tolerance of juvenile speckled peacock bass Cichla temensis

The speckled peacock bass Cichla temensis is a popular sport and food fish that generates substantial angling tourism and utilitarian harvest within its range. Its popularity and value make this species important for management and a potential aquaculture candidate for both fisheries enhancement and food fish production. However, little is known of optimal physiochemical conditions in natural habitats, which also are important for the development of hatchery protocols for handling, spawning and grow-out. Speckled peacock bass have been documented to have high sensitivity to extreme temperatures, but the metabolic underpinnings have not been evaluated. In this study, the effects of temperature (25, 30 and 35°C) on the standard metabolic rate (SMR) and lower dissolved oxygen tolerance (LDOT) of juvenile speckled peacock bass (mean ± standard error total length 153 ± 2 mm and wet weight 39.09 ± 1.37 g) were evaluated using intermittent respirometers after an acclimation period of 2 weeks. Speckled peacock bass had the highest SMR at 35°C (345.56 ± 19.89 mgO₂ kg⁻¹ h⁻¹), followed by 30°C (208.16 ± 12.45 mgO₂ kg⁻¹ h⁻¹) and 25°C (144.09 ± 10.43 mgO₂ kg⁻¹ h⁻¹). Correspondingly, the Q₁₀, or rate of increase in aerobic metabolic rate (MO₂) relative to 10°C, for 30–35°C was also greater (2.76) than from 25 to 30°C (2.08). Similarly, speckled peacock bass were the most sensitive to hypoxia at the warmest temperature, with an LDOT at pO₂ of 90 mmHg (4.13 mg l⁻¹) at 35°C compared to pO₂ values of 45 mmHg (2.22 mg l⁻¹) and 30 mmHg (1.61 mg l⁻¹) at 30 and 25°C, respectively. These results indicate that speckled peacock bass are sensitive to temperatures near 35°C, therefore we recommend managing and rearing this species at 25–30°C.     

Aerobic swimming performance of juvenile Schizothorax chongi (Pisces, Cyprinidae) in the Yalong River, southwestern China

Schizothorax chongi (locally known as Xilian Yu), a fish species commonly found in Yalong River, has been declining quickly in recent years. One of the important factors, among many, is the interruption of the free flowing river by dams. To obtain data that can be applied to the design of a fishway for S. chongi and other species in the community, a laboratory study of juvenile S. chongi’s swimming energetics and kinematics was conducted in a flume-type respirometer equipped with a high speed video camera system to record swimming behavior. The aerobic metabolic rate, tail beat frequency (TBF) and tail beat amplitude (TBA) were measured during steady swimming at varying flow rates for fish of similar mass. A power function accurately describes the relationship between oxygen consumption rate (MO₂) and swimming speed (U). The estimated standard metabolic rate (SMR) calculated from the power function was 445.34 mg O₂ kg⁻¹ h⁻¹, similar to the experimental result of 431.5 mg O₂ kg⁻¹ h⁻¹. The relationship between cost of transport (COT) and U was, characteristically, inverse bell-shaped, with COT_min = 44.6 J kg⁻¹ m⁻¹ at U _opt = 5.5 body lengths per second (bl s⁻¹). There was a significant positive linear correlation between TBF and U. The slope of the correlation (0.33) was lower than for many other species, implying that S. chongi swim efficiently. The TBA, ranging from 0.15 to 0.2 bl, was found to be independent of U. Kinematic analyses indicates that S. chongi primarily depends on the caudal fin to generate forward thrust and employs three velocity-dependent swimming gaits. This investigation provides data on the swimming ability of S. chongi that will add to the basic science required for fishway design.     

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     

Validation of annulus in otolith and estimation of growth rate for Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> in tropical southern Taiwan

The age of Japanese eels (Anguilla japonica) is often estimated from otoliths, but this method has not been fully validated, particularly in tropical areas where the annulus in otolith is considered to be less distinct than in temperate areas. To validate the annuli in Japanese eel otoliths from southern Taiwan, known-age (2 year-old) cultured eels from an eel farm and wild eels from Kao-Ping River were collected. It was found that 26 out of 31 cultured eels (83.9%) showed two clear annuli and the remained 5 eels showed either one or three annuli. The mean (± SD) age of the cultured eels was 1.97 ± 0.4 years. Meanwhile, a clear peak in the mean monthly marginal increment ratio of the otolith in wild yellow and silver eels occurred once a year during winter (November to March). The annual deposition of presumed annuli in otoliths of Japanese eel was validated and the age and growth rate estimation for Japanese eels in the tropical southern Taiwan is deemed feasible. The growth rate of cultured eels was significantly faster than that of wild eels, but it did not differ significantly between sexes for wild silver, yellow or cultured eels. The von Bertalanffy Growth Function parameters (K, and t ₀ ) of the wild eels were estimated as 0.114 ± 0.028 year⁻¹, 1178 ± 171 mm and −0.8 ± 0.2 years, respectively.     

Biogeochemical conditions and ice algal photosynthetic parameters in Weddell Sea ice during early spring

Physical, biogeochemical and photosynthetic parameters were measured in sea ice brine and ice core bottom samples in the north-western Weddell Sea during early spring 2006. Sea ice brines collected from sackholes were characterised by cold temperatures (range −7.4 to −3.8°C), high salinities (range 61.4–118.0), and partly elevated dissolved oxygen concentrations (range 159–413 μmol kg⁻¹) when compared to surface seawater. Nitrate (range 0.5–76.3 μmol kg⁻¹), dissolved inorganic phosphate (range 0.2–7.0 μmol kg⁻¹) and silicic acid (range 74–285 μmol kg⁻¹) concentrations in sea ice brines were depleted when compared to surface seawater. In contrast, NH₄ ⁺ (range 0.3–23.0 μmol kg⁻¹) and dissolved organic carbon (range 140–707 μmol kg⁻¹) were enriched in the sea ice brines. Ice core bottom samples exhibited moderate temperatures and brine salinities, but high algal biomass (4.9–435.5 μg Chl a l⁻¹ brine) and silicic acid depletion. Pulse amplitude modulated fluorometry was used for the determination of the photosynthetic parameters F _v/F _m, α, rETR_max and E _k. The maximum quantum yield of photosystem II, F _v/F _m, ranged from 0.101 to 0.500 (average 0.284 ± 0.132) and 0.235 to 0.595 (average 0.368 ± 0.127) in the sea ice internal and bottom communities, respectively. The fluorometric measurements indicated medium ice algal photosynthetic activity both in the internal and bottom communities of the sea ice. An observed lack of correlation between biogeochemical and photosynthetic parameters was most likely due to temporally and spatially decoupled physical and biological processes in the sea ice brine channel system, and was also influenced by the temporal and spatial resolution of applied sampling techniques.     

Effects of acute temperature changes on the swimming abilities and oxygen consumption of Ptychobarbus kaznakovi from the Lancang River

Water temperature is known to be a particularly important environmental factor that affects fish swimming performance, but it is unknow how acute temperature changes affect the fish performance of Ptychobarbus kaznakovi. P. kaznakovi in the Lancang River have declined quickly in recent years, and this species was used to examine the effects of acute temperature changes on swimming abilities and oxygen consumption in a Brett‐type swimming tunnel respirometer. The standard metabolic rate (SMR) and routine metabolic rate (RMR) showed 216% and 134% increases, respectively, at 22°C (an acute increase from 17 to 22°C) compared to those at 12°C (an acute decrease from 17 to 12°C). Moreover, the RMR was approximately 1.7, 1.6 and 1.3 times the value of the SMR at 12°C, 17°C and 22°C, respectively. The critical swimming speed (U_crit) of P. kaznakovi at 22°C was 5.45 ± 0.45BL/S, which was 45% higher than that at 12°C (3.77 ± 0.92BL/S). The oxygen consumption rates (MO₂) reached their maximum values at swimming speeds near the U_crit for all the temperature treatments. The maximum metabolic rate (MMR) values at 12°C, 17°C and 22°C were 274.53 ± 142.60 (mgO₂ kg^?1 hr^?1), 412.85 ± 216.34 (mgO₂ kg^?1 hr^?1) and 1,095.73 ± 52.50 (mgO₂ kg^?1 hr^?1), respectively. Moreover, there was a narrow aerobic scope at 12°C compared to that at 17°C and 22°C. The effect of acute temperature changes on the swimming abilities and oxygen consumption of P. kaznakovi indicated that water temperature changes caused by dam construction could directly affect energy consumption during the upstream migration of fish.     

The influence of chronic anaemia on catecholamine secretion in the rainbow trout (Oncorhynchus mykiss)

The effect of long-term (7 day) anaemia on catecholamine release was examined in rainbow trout (Oncorhynchus mykiss) in vivo during acute exposure to hypoxia and in situ using a perfused post-cardinal vein preparation. The first goal was to distinguish among reductions in blood O₂ partial pressure, O₂ concentration and haemoglobin percentage saturation as potential stimuli for, or correlates of, catecholamine secretion during hypoxia. The second goal was to elucidate the role of these factors in promoting enhanced chromaffin cell responsiveness in trout subjected to chronic hypoxia (Montpetit and Perry 1998). Anaemic fish (haematocrit lowered from 28.4±2.4% to 11.9±1.6%) displayed a marked reduction in haemoglobin-O₂ binding affinity [P ₅₀ (P _aO₂ at 50% Hb-O₂ saturation) was increased from 14.7 mm Hg to 24.3 mm Hg]. Upon exposure to hypoxia, the anaemic fish released catecholamines into their circulation at higher values of arterial O₂ partial pressure (∼52 mm Hg versus ∼18 mm Hg) and haemoglobin O₂ saturation (<70% versus <55%) than did control fish. In addition, anaemic fish achieved significantly greater circulating levels of total catecholamines (noradrenaline plus adrenaline) during acute hypoxia (294.8±67.3 versus 107.0±35.6 nmol l⁻¹). These results do not support the view that catecholamine release is triggered by a reduction in haemoglobin O₂ saturation or arterial PO₂, per se. Nor are they consistent with the idea that catecholamine release occurs at a threshold value of arterial PO₂ corresponding to a critical reduction in blood O₂ concentration. The effects of the non-selective cholinergic receptor carbachol on catecholamine secretion from chromaffin tissue were assessed using perfused posterior cardinal vein preparations derived from control or anaemic fish. For adrenaline secretion, there was no statistically significant change in the ED₅₀ (dose eliciting 50% response). For noradrenaline secretion however, preparations originating from anaemic fish displayed an enhanced responsiveness to carbachol as indicated by a significant 4.5-fold reduction in the carbachol ED₅₀ value from 2.53 × 10⁻⁶ mol kg⁻¹ to 5.67 × 10⁻⁷ mol kg⁻¹. These results demonstrate that anaemia-induced hypoxaemia, in the absence of any lowering of PO₂, is able to modulate the responsiveness of chromaffin cells to cholinergic stimulation. Accepted: 21 April 1999     

Soil particle accumulation in termite (Macrotermes bellicosus) mounds and the implications for soil particle dynamics in a tropical savanna Ultisol

This study investigated the influence of mound-building termites on soil particle dynamics on the land surface and in soil-forming processes by examining the amount of soil particles in mound structures of Macrotermes bellicosus in a highly weathered Ultisol of tropical savanna. Soil particle turnover via the mounds was estimated using particle stock data and soil turnover data from previous studies. A 4-ha study plot with six mounds of relatively uniform shape and size was investigated. Soil mass constituting the mounds was 6,166 ± 1,581 kg mound⁻¹ within which the mound wall and nest body accounted for 5,002 ± 1,289 and 1,164 ± 293 kg, respectively. The mound wall contained a significantly larger amount of clay (252 ± 9.97 g kg⁻¹) balanced with a lower sand content (676 ± 26.5 g kg⁻¹) than in the adjacent surface (Ap1) horizon, (46.4 ± 12.8 g clay kg⁻¹; 866 ± 83.2 g sand kg⁻¹); the nest body had much higher clay content (559 ± 51.0 g kg⁻¹) but less sand (285 ± 79.2 g kg⁻¹) than the mound wall. As a result, the mounds of M. bellicosus accumulated clay of 2,874 ± 781 kg ha⁻¹ (corresponding to 2.52% of clay stock in the Ap1 horizon) along with an estimated clay turnover rate of 169 kg ha⁻¹ year⁻¹. These findings suggest a positive feedback effect from termite mound-building activity on soil particle dynamics in tropical savanna ecosystems: M. bellicosus preferentially use subsoil material for mound construction, resulting in relocation of illuvial clay in the subsoil to the land surface where clay eluviation from the surface soil and its illuviation in the subsoil are major soil-forming processes.     

Quadrupedal locomotor performance in two species of arboreal squirrels: predicting energy savings of gliding

Gliding allows mammals to exploit canopy habitats of old-growth forests possibly as a means to save energy. To assess costs of quadrupedal locomotion for a gliding arboreal mammal, we used open-flow respirometry and a variable-speed treadmill to measure oxygen consumption and to calculate cost of transport, excess exercise oxygen consumption, and excess post-exercise oxygen consumption for nine northern flying squirrels (Glaucomys sabrinus) and four fox squirrels (Sciurus niger). Our results indicate that oxygen consumption during exercise by flying squirrels was 1.26–1.65 times higher than predicted based on body mass, and exponentially increased with velocity (from 0.84 ± 0.03 ml O₂ kg⁻¹ s⁻¹ at 0.40 m s⁻¹ to 1.55 ± 0.03 ml O₂ kg⁻¹ s⁻¹ at 0.67 m s⁻¹). Also, cost of transport in flying squirrels increased with velocity, although excess exercise oxygen consumption and excess post-exercise oxygen consumption did not. In contrast, oxygen consumption during exercise for fox squirrels was similar to predicted, varying from 0.51 (±0.02) ml O₂ kg⁻¹ s⁻¹ at 0.63 m s⁻¹ to 0.54 (±0.03) ml O₂ kg⁻¹ s⁻¹ at 1.25 m s⁻¹. In addition, the cost of transport for fox squirrels decreased with velocity, while excess exercise oxygen consumption and excess post-exercise oxygen consumption did not. Collectively, these observations suggest that unlike fox squirrels, flying squirrels are poorly adapted to prolonged bouts of quadrupedal locomotion. The evolution of skeletal adaptations to climbing, leaping, and landing and the development of a gliding membrane likely has increased the cost of quadrupedal locomotion by >50% while resulting in energy savings during gliding and reduction in travel time between foraging patches.     

Fluxes of greenhouse gases from Andosols under coffee in monoculture or shaded by <Emphasis Type="Italic">Inga densiflora</Emphasis> in Costa Rica

The objective of this study was to evaluate the effect of N fertilization and the presence of N₂ fixing leguminous trees on soil fluxes of greenhouse gases. For a one year period, we measured soil fluxes of nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄), related soil parameters (temperature, water-filled pore space, mineral nitrogen content, N mineralization potential) and litterfall in two highly fertilized (250 kg N ha⁻¹ year⁻¹) coffee cultivation: a monoculture (CM) and a culture shaded by the N₂ fixing legume species Inga densiflora (CIn). Nitrogen fertilizer addition significantly influenced N₂O emissions with 84% of the annual N₂O emitted during the post fertilization periods, and temporarily increased soil respiration and decreased CH₄ uptakes. The higher annual N₂O emissions from the shaded plantation (5.8 ± 0.3 kg N ha⁻¹ year⁻¹) when compared to that from the monoculture (4.3 ± 0.1 kg N ha⁻¹ year⁻¹) was related to the higher N input through litterfall (246 ± 16 kg N ha⁻¹ year⁻¹) and higher potential soil N mineralization rate (3.7 ± 0.2 mg N kg⁻¹ d.w. d⁻¹) in the shaded cultivation when compared to the monoculture (153 ± 6.8 kg N ha⁻¹ year⁻¹ and 2.2 ± 0.2 mg N kg⁻¹ d.w. d⁻¹). This confirms that the presence of N₂ fixing shade trees can increase N₂O emissions. Annual CO₂ and CH₄ fluxes of both systems were similar (8.4 ± 2.6 and 7.5 ± 2.3 t C-CO₂ ha⁻¹ year⁻¹, −1.1 ± 1.5 and 3.3 ± 1.1 kg C-CH₄ ha⁻¹ year⁻¹, respectively in the CIn and CM plantations) but, unexpectedly increased during the dry season.     

The development of an isokinetic squat device: reliability and relationship to functional performance

The aims of the present study were: (1) to assess aerobic metabolism in paraplegic (P) athletes (spinal lesion level, T4–L3) by means of peak oxygen uptake (V˙O_2peak) and ventilatory threshold (VT), and (2) to determine the nature of exercise limitation in these athletes by means of cardioventilatory responses at peak exercise. Eight P athletes underwent conventional spirographic measurements and then performed an incremental wheelchair exercise on an adapted treadmill. Ventilatory data were collected every minute using an automated metabolic system: ventilation (l · min⁻¹), oxygen uptake (V˙O₂, l · min⁻¹, ml · min⁻¹ · kg⁻¹), carbon dioxide production (V˙CO₂, ml · min⁻¹), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats · min⁻¹) was collected with the aid of a standard electrocardiogram. V˙O_2peak was determined using conventional criteria. VT was determined by the breakpoint in the V˙CO₂−V˙O₂ relationship, and is expressed as the absolute VT (V˙O₂, ml · min⁻¹ · kg⁻¹) and relative VT (percentage of V˙O_2peak). Spirometric values and cardioventilatory responses at rest and at peak exercise allowed the measurement of ventilatory reserve (VR), heart rate reserve (HRr), heart rate response (HRR), and O₂ pulse (O₂ P). Results showed a V˙O_2peak value of 40.6 (2.5) ml · min⁻¹ · kg⁻¹, an absolute VT detected at 23.1 (1.5) ml · min⁻¹ · kg⁻¹ V˙O₂ and a relative VT at 56.4 (2.2)% V˙O_2peak. HRr [15.8 (3.2) beats · min⁻¹], HRR [48.6 (4.3) beat · l⁻¹], and O₂ P [0.23 (0.02) ml · kg⁻¹ · beat⁻¹] were normal, whereas VR at peak exercise [42.7 (2.4)%] was increased. As wheelchair exercise excluded the use of an able-bodied (AB) control group, we compared our V˙O_2peak and VT results with those for other P subjects and AB controls reported in the literature, and we compared our cardioventilatory responses with those for respiratory and cardiac patients. The low V˙O_2peak values obtained compared with subject values obtained during an arm-crank exercise may be due to a reduced active muscle mass. Absolute VT was somewhat comparable to that of AB subjects, mainly due to the similar muscle mass involved in wheelchair and arm-crank exercise by P and AB subjects, respectively. The increased VR, as reported in patients with chronic heart failure, suggested that P athletes exhibited cardiac limitation at peak exercise, and this contributed to the lower V˙O_2peak measured in these subjects. Accepted: 22 April 1997     

Identification and characterization of 4-hexylbenzoic acid and 4-nonyloxybenzoic acid as substrates of CYP102A1

CYP102A1 is an efficient medium- to long-chain fatty acid hydroxylase that is able to accept a wide range of non-natural substrates which bear no resemblance to the natural ones. 4-Hexylbenzoic acid (HBA) and 4-nonyloxybenzoic acid (NOBA) were identified as CYP102A1 substrates via screening studies using the BD Oxygen Biosensor System. Spectroscopic binding studies showed that these two substrates bind in the active site of CYP102A1 with K _d values of 2.6 ± 0.1 μM for HBA and 1.9 ± 0.2 μM for NOBA. NADPH consumption rates in the presence of HBA and NOBA were 45 ± 1 min⁻¹ and 61 ± 1 min⁻¹, respectively. The coupling efficiency for NADPH was 57% for NOBA, while it was 77% for HBA. During whole-cell biotransformations, HBA was converted into ω−1- and ω−2-hydroxyhexylbenzoic acid, whereas NOBA was oxidized to ω−2-hydroxynonyloxybenzoic acid and ω−2,ω−4-dihydroxynonyloxybenzoic acid. HBA was used as a fatty acid mimic to compare whole-cell biotransformations with cell-free extracts. Whole-cell biotransformations carried out in a biphasic system resulted in 86% conversion of 5 mM HBA, producing 3.8 mM ω−2- and 0.5 mM ω−1-hydroxyhexylbenzoic acid in 4 h with a turnover number of 4.1 min⁻¹, whereas 100% conversion of 5 mM HBA was obtained in 1 h with crude cell extracts and a cofactor regeneration system, giving a turnover number of 10.5 min⁻¹.     

Effect of intense interval workouts on running economy using three recovery durations

The purposes of this study were to determine whether running economy (RE) is adversely affected following intense interval bouts of 10 × 400-m running, and whether there is an interaction effect between RE and recovery duration during the workouts. Twelve highly trained male endurance athletes [maximal oxygen consumption; V˙O_{2 max} =72.5 (4.3) ml·kg⁻¹·min⁻¹; mean (SD)] performed three interval running workouts of 10 × 400 m with a minimum of 4 days between runs. Recovery duration between the repetitions was randomly assigned at 60, 120 or 180 s. The velocity for each 400-m run was determined from a treadmill V˙O_{2 max} test. The average running velocity was 357.9 (9.0) m · min⁻¹. Following the workout, the rating of perceived exertion (RPE) increased significantly (P < 0.01) as recovery duration between the 400-m repetitions decreased (14.4, 16.1, and 17.7 at 180s, 120s, and 60 s recovery, respectively). Prior to and following each workout, RE was measured at speeds of 200 and 268 m · min⁻¹. Changes in RE from pre- to post-workout, as well as heart rate (HR) and respiratory exchange ratio (R) were similar for the three recovery conditions. When averaged across conditions, oxygen consumption (V˙O₂) increased significantly (P < 0.01) from pre- to post-test (from 38.5 to 40.5 ml · kg⁻¹ · min⁻¹ at 200 m · min⁻¹, and from 53.1 to 54.5 ml · kg⁻¹ · min⁻¹ at 268 m · min⁻¹, respectively). HR increased (from 124 to 138, and from 151 to 157 beats · min⁻¹ respectively) and R decreased (from 0.90 to 0.78, and from 0.93 to 0.89, respectively) at 200 and 268 m · min⁻¹, respectively (P < 0.01). This study showed that RE can be perturbed after a high-intensity interval workout and that the changes in V˙O₂, HR and R were independent of the recovery duration between the repetitions. Accepted: 23 June 1997     

Effects of warm acclimation on serum osmolality,cortisol and hematocrit levels in the Antarctic fish, <Emphasis Type="Italic">Trematomus bernacchii</Emphasis>

Antarctic fish, such as the Trematomus bernacchii, living at −1.9°C maintain a serum osmolality of around 600 mOsm kg⁻¹, nearly twice that of temperate fish. Upon warm acclimation, Antarctic fish significantly lower their serum osmolality. It has been suggested that this response to warm acclimation is due to stress. The purpose of this study was to determine, whether upon warm acclimation there was a change in the levels of the stress hormone cortisol and hematocrit associated with the decrease in serum osmolality. T. bernacchii were warm acclimated up to 4 weeks and serum osmolality, cortisol and hematocrit were measured. Upon warm acclimation to +1.6 and +3.8°C over the course of 4 weeks, T. bernacchii significantly lowered their serum osmolality (from 547 ± 4 mOsm kg⁻¹ to 494 ± 6 and 489 ± 4 mOsm kg⁻¹, respectively), yet did not alter their serum cortisol (29 ± 6 nl ml⁻¹) or hematocrit (22 ± 1%) levels. These results suggest that warm acclimation does not induce a stress response in T. bernacchii.     

A new manganese superoxide dismutase identified from Beauveria bassiana enhances virulence and stress tolerance when overexpressed in the fungal pathogen

A superoxide dismutase (SOD) was characterized from Beauveria bassiana, a fungal entomopathogen widely applied to insect control. This 209-aa enzyme (BbSod2) showed no more than 71% sequence identity to other fungal Mn-SODs, sharing all conserved residues with the Mn-SOD family and lacking a mitochondrial signal. The SOD activity of purified BbSod2 was significantly elevated by Mn²⁺, suppressed by Cu²⁺ and Zn²⁺ but inhibited by Fe³⁺. Overexpressing the enzyme in a BbSod2-absent B. bassiana strain enhanced its SOD activity (107.2 ± 6.1 U mg⁻¹ protein) by 4–10-fold in different transformants analyzed. The best BbSod2-transformed strain with the SOD activity of 1,157.9 ± 74.7 U mg⁻¹ was 93% and 61% more tolerant to superoxide-generating menadione in both colony growth (EC₅₀ = 2.41 ± 0.03 versus 1.25 ± 0.01 mM) and conidial germination (EC₅₀ = 0.89 ± 0.06 versus 0.55 ± 0.07 mM), and 23% more tolerant to UV-B irradiation (LD₅₀ = 0.49 ± 0.02 versus 0.39 ± 0.01 J cm⁻²). Its virulence to Spodoptera litura larvae was enhanced by 26% [LT₅₀ = 4.5 (4.2–4.8) versus 5.7 (5.2–6.4) days]. Our study highlights for the first time that the Mn²⁺-cofactored, cytosolic BbSod2 contributes significantly to the virulence and stress tolerance of B. bassiana and reveals possible means to improving field persistence and efficacy of a fungal formulation by manipulating the antioxidant enzymes of a candidate strain.     

Running economy deteriorates following 60?min of exercise at 80% V˙O2max

Fifteen young adult Singaporean male physical education students maximum oxygen consumption [(V˙O_2max) = 56 (4.7) ml · kg⁻¹ · min⁻¹] performed three prolonged runs in a counterbalanced design. The running bouts varied in time (40 vs 60 min) and intensity (70% vs 80% V˙O_{2 max} ). Each prolonged run was separated by 7 days. The running economy (RE) at 10.8 km · h⁻¹ during 10-min running bouts was measured before (RE1) and after (RE2) each prolonged run. A control study involved monitoring RE at 10.8 km · h⁻¹ before and after 60 min rest. There were no differences between RE1 and RE2 values during the control run. However, there were differences between RE1 and RE2 values when separated by a prolonged run. For example, the mean (SD) changes in oxygen consumption (ml · kg⁻¹ · min⁻¹) values were 38.2 (2.5) versus 40.1 (2.6) (40 min at 80% V˙O_{2 max} ), 38.9 (2.8) versus 41.5 (2.6) (60 min at 70% V˙O_{2 max} ), and 39.0 (3.1) versus 42.7 (2.9) (60 min at 80% V˙O_{2 max} ; P < 0.01). The results of this investigation support the hypothesis that RE deteriorates during prolonged running, and that the magnitude of the deterioration in RE increases with both increasing exercise intensity and duration. Accepted: 14 July 1997     

Measurement of activity concentrations of <Superscript>40</Superscript>K, <Superscript>226</Superscript>Ra and <Superscript>232</Superscript>Th for assessment of radiation hazards from soils of the southwestern region of Nigeria

Activity concentrations of the selected radionuclides ⁴⁰K, ²²⁶Ra and ²³²Th were measured in surface soil samples collected from 38 cities in the southwest region of Nigeria by means of gamma spectroscopy with a high-purity germanium detector. Measured activity concentration values of ⁴⁰K varied from 34.9 ± 4.4 to 1,358.6 ± 28.5 Bq kg⁻¹ (given on a dry mass (DM) basis) with a mean value of 286.5 ± 308.5 Bq kg⁻¹; that of ²²⁶Ra varied from 9.3 ± 3.7 to 198.1 ± 13.8 Bq kg⁻¹ with a mean value of 54.5 Bq kg⁻¹ and a standard deviation of 38.7 Bq kg⁻¹, while that of ²³²Th varied from 5.4 ± 1.1 to 502.0 ± 16.5 Bq kg⁻¹ with a mean value of 91.1 Bq kg⁻¹ and standard deviation of 100.9 Bq kg⁻¹. The mean activity concentration values obtained for ²²⁶Ra and ²³²Th are greater than the world average values reported by the United Nations Scientific Committee on Effects of Atomic Radiation for areas of normal background radiation. Radiological indices were estimated for the radiation/health hazards of the natural radioactivity of all soil samples. Estimated absorbed dose rates in air varied from 12.42 ± 2.25 to 451.33 ± 19.06 nGy h⁻¹, annual outdoor effective dose rates from 0.015 ± 0.003 to 0.554 ± 0.023 mSv year⁻¹, internal hazard index from 0.10 ± 0.03 to 3.02 ± 0.16, external hazard index from 0.07 ± 0.01 to 2.60 ± 0.11, representative level index from 0.19 ± 0.03 to 6.84 ± 0.29, activity index from 0.09 ± 0.02 to 3.42 ± 0.15, and radium equivalent activity from 26.95 ± 5.04 to 963.15 ± 41.87 Bq kg⁻¹. Only the mean value of the representative level index exceeds the limit for areas of normal background radiation. All other indices show mean values that are lower than the recommended limits.