Stroke volume response to progressive exercise in athletes engaged in different types of training

Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

A reduced core to skin temperature gradient,not a critical core temperature,affects aerobic capacity in the heat

The purpose of this study was to determine the impact of the core to skin temperature gradient during incremental running to volitional fatigue across varying environmental conditions. A secondary aim was to determine if a “critical” core temperature would dictate volitional fatigue during running in the heat. 60 participants (n=49 male, n=11 female; 24±5 yrs, 177±11 cm, 75±13 kg) completed the study. Participants were uniformly stratified into a specific exercise temperature group (18 °C, 26 °C, 34 °C, or 42 °C) based on a 3-mile run performance. Participants were equipped with core and chest skin temperature sensors and a heart rate monitor, entered an environmental chamber (18 °C, 26 °C, 34 °C, or 42 °C), and rested in the seated position for 10 min before performing a walk/run to volitional exhaustion. Initial treadmill speed was 3.2 km h⁻¹ with a 0% grade. Every 3 min, starting with speed, speed and grade increased in an alternating pattern (speed increased by 0.805 km h⁻¹, grade increased by 0.5%). Time to volitional fatigue was longer for the 18 °C and 26 °C group compared to the 42 °C group, (58.1±9.3 and 62.6±6.5 min vs. 51.3±8.3 min, respectively, p<0.05). At the half-way point and finish, the core to skin gradient for the 18 °C and 26 °C groups was larger compared to 42 °C group (halfway: 2.6±0.7 and 2.0±0.6 vs. 1.3±0.5 for the 18 °C, 26 °C and 42 °C groups, respectively; finish: 3.3±0.7 and 3.5±1.1 vs. 2.1±0.9 for the 26 °C, 34 °C, and 42 °C groups, respectively, p<0.05). Sweat rate was lower in the 18 °C group compared to the 26 °C, 34 °C, and 42 °C groups, 3.6±1.3 vs. 7.2±3.0, 7.1±2.0, and 7.6±1.7 g m⁻² min⁻¹, respectively, p<0.05. There were no group differences in core temperature and heart rate response during the exercise trials. The current data demonstrate a 13% and 22% longer run time to exhaustion for the 18 °C and 26 °C group, respectively, compared to the 42 °C group despite no differences in beginning and ending core temperatures or baseline 3-mile run time. This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.     

Elevated atmospheric CO2 does not affect per se the preference for symbiotic nitrogen as opposed to mineral nitrogen of Trifolium repens L.

The objective of this investigation was to examine the effect of an elevated atmospheric CO₂ partial pressure ( p CO₂) on the N-sink strength and performance of symbiotic N₂ fixation in Trifolium repens L. cv. Milkanova. After initial growth under ambient p CO₂ in a nitrogen-free nutrient solution, T. repens in the exponential growth stage was exposed to ambient and elevated p CO₂ (35 and 60 Pa) and two levels of mineral N (N-free and 7·5 mol m^–3 N) for 36 d in single pots filled with silica sand in growth chambers. Elevated p CO₂ evoked a significant increase in biomass production from day 12 after the start of CO₂ enrichment. For plants supplied with 7·5 mol m^–3 N, the relative contribution of symbiotically fixed N (%N_sym) as opposed to N assimilated from mineral sources (¹⁵N-isotope-dilution method), dropped to 40%. However, in the presence of this high level of mineral N, %N_sym was unaffected by atmospheric p CO₂ over the entire experimental period. In plants fully dependent on N₂ fixation, the increase in N yield reflects a stimulation of symbiotic N₂ fixation that was the result of the formation of more nodules rather than of higher specific N₂ fixation. These results are discussed with regard to physiological processes governing symbiotic N₂ fixation and to the response of symbiotic N₂ fixation to elevated p CO₂ in field-grown T. repens .     

Elevated temperature reduces survivorship and settlement of the larvae of the Caribbean scleractinian coral, Favia?fragum (Esper)

The effect of elevated seawater temperatures, such as those plaguing tropical seas during the summers of anomalously warm years, on early life stages of reef corals remains poorly studied. To redress this situation, survivorship of larvae of the brooding coral, Favia fragum, was studied in the laboratory, using both short term (48 h) and long term (156–191 h) exposures to 28, 29, and 31°C. Ability to settle when presented with induction substrates and survival after settlement, at the same exposure temperature and after reciprocal transfers to the other experimental temperatures, were also measured. No significant effect of temperature on survivorship was detected after 48 h of exposure, but larvae incubated for 156 h at the highest temperature (31°C) exhibited a 13% reduced survivorship compared to larvae at 28°C. Induction of settlement further increased mortality at the highest temperature (31°C); survivorship after settlement at 31°C was 27% lower than when larvae were simply maintained at the elevated temperature. These results indicate that elevated temperatures are more detrimental to coral larvae undergoing the developmentally complex settlement process than to the swimming planula stage. This may bode poorly for Caribbean corals with late summer reproductive seasons. Communicated by Ecology Editor Prof. Peter Mumby     

Elevated seasonal temperature disrupts prooxidant-antioxidant homeostasis and promotes cellular apoptosis in the American oyster,Crassostrea virginica,in the Gulf of Mexico: a field study

One of the major impacts of climate change has been the marked rise in global temperature. Recently, we demonstrated that high temperatures (1-week exposure) disrupt prooxidant-antioxidant homeostasis and promote cellular apoptosis in the American oyster. In this study, we evaluated the effects of seasonal sea surface temperature (SST) on tissue morphology, extrapallial fluid (EPF) conditions, heat shock protein-70 (HSP70), dinitrophenyl protein (DNP, an indicator of reactive oxygen species, ROS), 3-nitrotyrosine protein (NTP, an indicator of RNS), catalase (CAT), superoxide dismutase (SOD) protein expressions, and cellular apoptosis in gills and digestive glands of oysters collected on the southern Texas coast during the winter (15 °C), spring (24 °C), summer (30 °C), and fall (27 °C). Histological observations of both tissues showed a notable increase in mucus production and an enlargement of the digestive gland lumen with seasonal temperature rise, whereas biochemical analyses exhibited a significant decrease in EPF pH and protein concentration. Immunohistochemical analyses showed higher expression of HSP70 along with the expression of DNP and NTP in oyster tissues during summer. Intriguingly, CAT and SOD protein expressions exhibited significant upregulation with rising seasonal temperatures (15 to 27 °C), which decreased significantly in summer (30 °C), leaving oysters vulnerable to oxidative and nitrative damage. qRT-PCR analysis revealed a significant increase in HSP70 mRNA levels in oyster tissues during the warmer seasons. In situ TUNNEL assay showed a significant increase in apoptotic cells in seasons with high temperature. These results suggest that elevated SST induces oxidative/nitrative stress through the overproduction of ROS/RNS and disrupts the antioxidant system which promotes cellular apoptosis in oysters.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12192-021-01232-2.     

An experimental test of the role of environmental temperature variability on ectotherm molecular, physiological and life-history traits: implications for global warming

Global climate change is one of the greatest threats to biodiversity; one of the most important effects is the increase in the mean earth surface temperature. However, another but poorly studied main characteristic of global change appears to be an increase in temperature variability. Most of the current analyses of global change have focused on mean values, paying less attention to the role of the fluctuations of environmental variables. We experimentally tested the effects of environmental temperature variability on characteristics associated to the fitness (body mass balance, growth rate, and survival), metabolic rate (VCO(2)) and molecular traits (heat shock protein expression, Hsp70), in an ectotherm, the terrestrial woodlouse Porcellio laevis. Our general hypotheses are that higher values of thermal amplitude may directly affect life-history traits, increasing metabolic cost and stress responses. At first, results supported our hypotheses showing a diversity of responses among characters to the experimental thermal treatments. We emphasize that knowledge about the cellular and physiological mechanisms by which animals cope with environmental changes is essential to understand the impact of mean climatic change and variability. Also, we consider that the studies that only incorporate only mean temperatures to predict the life-history, ecological and evolutionary impact of global temperature changes present important problems to predict the diversity of responses of the organism. This is because the analysis ignores the complexity and details of the molecular and physiological processes by which animals cope with environmental variability, as well as the life-history and demographic consequences of such variability.     

Hardness does not affect the physiological responses of wild and domestic strains of diploid and triploid rainbow trout Oncorhynchus mykiss to short‐term exposure to pH 9.5

This study examined the effects of water hardness on the physiological responses associated with high pH exposure in multiple strains of diploid and triploid rainbow trout Oncorhynchus mykiss. To accomplish this, three wild strains and one domesticated strain of diploid and triploid O. mykiss were abruptly transferred from control soft water (City of Vancouver dechlorinated tap water; pH 6·7; [CaCO₃] < 17·9 mg l^?1) to control soft water (handling control), high pH soft water (pH 9·5; [CaCO₃] < 17·9 mg l^?1), or high pH hard water (pH 9·5; [CaCO₃] = 320 mg l^?1) followed by sampling at 24 h for physiological measurements. There was a significant effect of ploidy on loss of equilibrium (LOE) over the 24 h exposure, with only triploid O. mykiss losing equilibrium at high pH in both soft and hard water. Furthermore, exposure to pH 9·5 resulted in significant decreases in plasma sodium and chloride, and increases in plasma and brain ammonia with no differences between soft and hard water. There was no significant effect of strain on LOE, but there were significant differences between strains in brain ammonia and plasma cortisol. Overall, there were no clear protective effects of hardness on high pH exposure in these strains of O. mykiss.     

Response of cold-acclimated,farmed South African abalone (Haliotis midae) to short-term and long-term changes in temperature

In its natural environment, the South African abalone, Haliotis midae, occurs at average monthly water temperatures between 12 and 21 °C. In the present study we aimed to describe selected physiological and molecular responses of winter acclimated, cultured H. midae after acute and chronic exposure to 16, 19 and 22 °C.     

Behavioral and mortality responses of the bivalves Scrobicularia plana and Cerastoderma edule to temperature,as indicator of climate change's potential impacts

Temperature is one of the most important abiotic factors affected by climate change. It determines physiological processes, ecological patterns and establishes the limits of geographic distribution of species. The induced thermal stress frequently results in physiological and behavioral responses and, in extreme cases, may lead to mortality episodes. Scrobicularia plana and Cerastoderma edule behavioral and mortality responses to temperature were evaluated. Specimens were sampled in the Mondego estuary (Portugal), acclimated and exposed to different temperature treatments (5–35 °C). Individual activity and mortality were registered during 120 h laboratory assays. Both species showed a thermal optimum for their activity (S. plana: 15–23 °C; C. edule: 20–23 °C), and survival was mainly affected by high temperature (S. plana: LC50_120 h = 28.86 °C; C. edule: LC50_120 h = 28.01 °C), with 100% mortality above critical values (≥32 °C). Results further indicated that both species are more affected the higher the temperature and the longer the exposure time. This study indicates that the occurrence of extreme climatic events, especially heat waves, may be particularly impairing for these species.     

Stress‐driven increase in proline levels,and not proline levels themselves,correlates with the ability to withstand excess salt in a group of 17 Italian rice genotypes

• In most plant species, a rapid increase in free proline content occurs following exposure to hyperosmotic stress conditions. However, inconsistent results were reported concerning the role of such an increase on the plant response to water shortage or excess salt. Therefore, the possibility that proline accumulation may help the cell to withstand stress conditions, or that it simply represents a stress marker, is still a matter of debate. A possible relationship between proline accumulation and salt tolerance was investigated in a set of 17 Italian rice varieties.
• Rice seedlings were exposed to increasing salt concentrations during germination and early growth. The resulting levels of free proline were measured separately in shoots and roots and compared to those in untreated controls. Results were related to the corresponding ability of a given genotype to tolerate stress conditions.
• Neither absolute proline levels in untreated or in salt‐stressed seedlings showed a straightforward relationship to the relative tolerance to salt, estimated as conductivity values able to reduce growth by 10 or 50%. Conversely, a highly significant correlation was found between the increase in proline levels in shoots and the ability to withstand stress.
• The results strengthen a recent hypothesis suggesting than an increase in proline metabolic rates, more than the resulting proline content, may help the cell to counteract the effects of abiotic stress conditions.

     

Involvement of cortisol and sirtuin1 during the response to stress of hypothalamic circadian system and food intake-related peptides in rainbow trout,Oncorhynchus mykiss

Stress is conditioning animal welfare by negatively affecting a wide range of physiological and behavioral functions. This may be applied to circadian physiology and food intake. Cortisol, the stress-related hormone, may mediate such effect of stress, but other indirect mediators might be considered, such as sirtuin1. Then, either the independent modulatory effect or the existence of any interaction between mediators may be responsible. The circadian system is the main modulator of several integrative mechanisms at both central and peripheral levels that are rhythmically presented, thus influencing different processes such as food intake. In this way, food intake is controlled by the circadian system, as demonstrated by the persistence of such rhythms of food intake in the absence of environmental external cues. Our study aimed to evaluate the daily profile of hypothalamic mRNA abundance of circadian clock genes (clock1a, bmal1, per1 and rev-erbβ-like), and food intake regulators (crf, pomc-a1, cart, and npy) in rainbow trout (Oncorhynchus mykiss), the impact of stress on such rhythms, and the involvement of cortisol and sirtuin1 as mediators. Four cohorts of trout were subjected to 1) normal stocking density (control group), 2) high stocking density for 72 hours (stress group), 3) normal stocking density and implanted with mifepristone, a glucocorticoid receptors antagonist, and 4) mifepristone administered and stressed for 72 hours. Fish from each group were sampled every 4-h along the 24-h LD cycle, and cortisol, glucose and lactate plasma levels were evaluated. Hypothalamic mRNA abundance of clock genes, food intake regulators, glucocorticoid receptors and sirtuin1 were qPCR assayed. Our results reveal the impact of stress on most of the genes assayed, but different mechanisms appear to be involved. The rhythm of clock genes displayed decreased amplitude and averaged levels in stressed trout, with no changes of the acrophase being observed. This effect was not prevented by mifepristone. On the contrary, the effect of stress on the daily profile of crf, pomc-a1, and npy was totally prevented by mifepristone administration. Accordingly, cortisol appears to mainly mediate the effect of stress on food intake regulators through binding to specific glucocorticoid receptors within trout hypothalamus, whereas sirtuin1 is apparently mediating such effects on the circadian system in the same brain region. Further research must be performed to clarify those mechanisms through which stress influences food intake and the circadian oscillator within the same brain region, hypothalamus, in rainbow trout, and the interaction among them all.     

Exposure to exogenous egg cortisol does not rescue juvenile Chinook salmon body size,condition, or survival from the effects of elevated water temperatures

Climate change is leading to altered temperature regimes which are impacting aquatic life, particularly for ectothermic fish. The impacts of environmental stress can be translated across generations through maternally derived glucocorticoids, leading to altered offspring phenotypes. Although these maternal stress effects are often considered negative, recent studies suggest this maternal stress signal may prepare offspring for a similarly stressful environment (environmental match). We applied the environmental match hypothesis to examine whether a prenatal stress signal can dampen the effects of elevated water temperatures on body size, condition, and survival during early development in Chinook salmon Oncorhynchus tshawytscha from Lake Ontario, Canada. We exposed fertilized eggs to prenatal exogenous egg cortisol (1,000 ng/ml cortisol or 0 ng/ml control) and then reared these dosed groups at temperatures indicative of current (+0°C) and future (+3°C) temperature conditions. Offspring reared in elevated temperatures were smaller and had a lower survival at the hatchling developmental stage. Overall, we found that our exogenous cortisol dose did not dampen effects of elevated rearing temperatures (environmental match) on body size or early survival. Instead, our eyed stage survival indicates that our prenatal cortisol dose may be detrimental, as cortisol‐dosed offspring raised in elevated temperatures had lower survival than cortisol‐dosed and control reared in current temperatures. Our results suggest that a maternal stress signal may not be able to ameliorate the effects of thermal stress during early development. However, we highlight the importance of interpreting the fitness impacts of maternal stress within an environmentally relevant context.     

Metabolic and ventilatory responses to hypoxia in two altitudinal populations of the toad, Bufo bankorensis

Effects of hypoxia on resting oxygen consumption ( ), lung ventilation, and heart rate at different ambient P_O2 were compared between lowland and high altitude populations of the toad, Bufo bankorensis. Resting decreased significantly in mild hypoxia (P_O2=120 mm Hg) at 10°C and in moderate hypoxia (P_O2=80 mm Hg) at 25°C in both altitudinal populations; however, resting did not differ significantly between the two populations. Numbers of lung ventilation periods (VP) and total inspired volume (V_L) did not change with P_O2 at 10°C, but did increase at moderate and severe hypoxia (40 mm Hg), respectively, at 25°C. Resting heart rates did not change during hypoxia and did not differ between altitude populations. The results suggest (1) the effect of P_O2 change on should be considered in future studies involving transfer of anurans to a different altitude; and (2) the metabolic and ventilatory physiology in B. bankorensis does not compensate for the low temperature and P_O2 at high altitude.     

急性心肌梗死患者心电图碎裂QRS波与左心室收缩功能、心率变异性及心脏事件的关系研究

目的:探讨急性心肌梗死患者心电图碎裂QRS(f QRS)波与左心室收缩功能、心率变异性及心脏事件的关系。方法:收集2018年1月～2020年1月期间于本院进行治疗的急性心肌梗死患者124例,对患者行心电图检查,根据患者心电图是否出现f QRS波分成f QRS组(59例)和无f QRS组(65例),采用多普勒超声诊断仪对两组患者的左心室收缩功能进行检测对比,并对两组患者进行24h动态心电图检查,对两组患者的心率变异性指标进行统计对比。对两组患者进行为期3个月的随访观察,统计对比两组患者随访期间心脏事件的发生率。结果:f QRS组患者的左室射血分数(LVEF)低于无f QRS组,左心室舒张末期容积(LVEDV)、左心室舒张末期内径(LVEDD)均高于无f QRS组(P0.05)。f QRS组患者总标准差(SDNN)、两个相邻RR间期互差(PNN50)、差值均方根(RMSSD)均低于无f QRS组(P0.05)。随访期间f QRS组患者的心脏事件发生率为35.59%(21/59),高于无f QRS组患者的13.85%(9/65)(P0.05)。结论:伴有心电图f QRS波急性心肌梗死患者的左心室收缩功能降低,心率变异性指标降低,且心脏不良事件发生率增加,心电图f QRS波在一定程度上可作为急性心肌梗死患者心功能、心率变异性及心脏事件发生的监测手段。     

Atmospheric CO2, plant nitrogen status and the susceptibility of plants to an acute increase in temperature

Abstract. Elevated levels of CO₂ in the atmosphere are expected to affect plant performance and may alter global temperature patterns. Changes in mean air temperatures that might be induced by rising levels of CO₂ and other greenhouse gases could also be accompanied by increased variability in daily temperatures such that acute increases in air temperature may be more likely than at present. Consequently, we investigated whether plants grown in a CO₂ enriched atmosphere would be differently affected by a heat shock than plants grown at ambient CO₂ levels. Plants of a C₃ annual (Abutilon theophrasti), a C₃ annual crop (Sinapis alba) and a C₄ annual (Amaranthus retroflexus) were grown from seed in growth chambers under either 400 or 700cm³ m^?3 CO₂, and were fertilized with either a high or low nutrient regime. Young seedlings of S. alba, as well as plants of all species in either the vegetative or reproductive phase of growth were exposed to a 4-h heat shock in which the temperature was raised an additional 14–23°C (depending on plant age). Total biomass and reproductive biomass were examined to determine the effect of CO₂, nutrient and heat shock treatments on plant performance. Heat shock, CO₂, and nutrient treatments, all had some significant effects on plant performance, but plants from both CO₂ treatments responded similarly to heat shocks. We also found, as expected, that plants grown under high CO₂ had dramatically decreased tissue N concentrations relative to plants grown under ambient conditions. We predicted that high-CO₂-grown plants would be more susceptible to a heat shock than ambient-CO₂-grown plants, because the reduced N concentrations of high-CO₂ grown plants could result in the reduced synthesis of heat shock proteins and reduced thermotolerance. Although we did not examine heat shock proteins, our results showed little relationship between plant nitrogen status and the ability of a plant to tolerate an acute increase in temperature.     

Over-expression of chloroplast-targeted Mn superoxide dismutase in cotton (Gossypium hirsutum L., cv. Coker 312) does not alter the reduction of photosynthesis after short exposures to low temperature and high light intensity

Transgenic cotton plants from several independently-transformed lines expressing a chimeric gene encoding a chloroplast-targeted Mn superoxide dismutase (SOD) from tobacco exhibit a three-fold increase in the total leaf SOD activity, strong Mn SOD activity associated with isolated chloroplasts, and a 30% and 20% increase in ascorbate peroxidase and glutathione reductase activities, respectively. The Mn SOD plants did exhibit a slightly enhanced protection against light-mediated, paraquat-induced cellular damage but only at 0.3 µM paraquat. In addition, photosynthetic rates at 10°C and 15°C were similar to those of controls, and the immediate recovery of photosynthesis after a 35-min exposure to 5°C and full sun was only slightly better than that for wild-type plants. The recovery for longer exposure times was comparable for both genotypes as was the deactivation of the H₂O₂-sensitive, Calvin-cycle enzyme, stromal fructose 1,6-bisphosphatase (FBPase). Compared to the controls, Mn SOD plant leaves in full sun prior to chilling stress had a lower activation of FBPase, a higher ratio of oxidized to reduced forms of ascorbate, and a higher total glutathione content. After 35 min at 5°C in full sunlight, total glutathione had risen in control leaves to 88% of the Mn SOD plant values, and oxidized to reduced ascorbate ratios were higher for both genotypes. However, an 80% increase in the ratio of oxidized to reduced glutathione occurred for Mn SOD plant leaves with no change for controls. This increased demand on the ascorbate-glutathione cycle is circumstantial evidence that high Mn SOD activity in the chloroplast leads to increased H₂O₂ pools that could, in some manner, affect photosynthetic recovery after a stress period. We postulate that the pool sizes of reduced ascorbate and glutathione may restrict the ability of the ascorbate-glutathione cycle to compensate for the increased activity of SOD in cotton over-producing mitochondrial Mn SOD in chloroplasts during short-term chilling/high light stress.