Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

Most small mammalian hibernators spend the hibernation season cycling between bouts of torpor (with low body temperature (T_b) approximating ambient temperature (T_a), depressed heart and oxygen consumption rates as low as 1% active rates) and interbout arousals (IBA) where animals will spontaneously and rapidly arouse from torpor and resume most physiological functions. Kidneys are involved in numerous physiological functions including filtering the blood of metabolic waste. Due to the dramatic metabolic depression experienced during torpor and previous limitations in methods, studies inadequately addressed filtration during torpor. Here, we directly monitored clearance of sinistrin from ground squirrel circulation for up to 45 h during torpor bouts using transdermal fluorometry. In active squirrels (both summer active and interbout aroused), clearance by the kidneys was rapid with a clearance half-life (t_1/2) of 47.8 ± 5.4 and 73.4 ± 7.9 min, respectively. In contrast, clearance by the kidneys in torpid squirrels held at T_a= 4 °C was greatly reduced, but measurable, with t_1/2 of 7,103 ± 1,073 min (~ 97 to 149-fold increase in clearance time vs. active squirrels). Consistent with predictions based on metabolism, clearance by the kidneys during torpor at T_a=12 °C resulted in much faster clearance times than at T_a = 4 °C (T_1/2= 2,761 ± 375 min; 2.57-fold increase vs. 4 °C; Q₁₀ = 3.26). We demonstrate that hibernators do not completely cease excretion functions during torpor but that clearance quickly commences even at low temperatures as soon as the squirrel begins to arouse.

Deep metabolic transitions promoted by anoxia and diapause are tolerated for years by embryos of the brine shrimp, Artemia franciscana, whereas even short metabolic disruptions in mammals are accompanied by bursts of reactive oxygen species (ROS) that cause tissue damage during ischemia-reperfusion. We hypothesized mitochondria from these embryos are mechanistically poised to avoid ROS bursts and the associated oxidative stress during metabolic recovery. Isolated mitochondria that exhibited robust functional coupling were exposed to anoxia-reoxygenation (A/R) or continuous normoxia. H₂O₂ efflux was statistically identical between A/R versus normoxia groups (p = 0.221). Addition of auranofin and dinitrochlorobenzene, inhibitors of ROS scavenging pathways, promoted a five-fold increase in H₂O₂ release for the normoxic mitochondria, which confirmed that scavenging mechanisms substantially suppress routine ROS efflux. Yet when these same inhibitors were added to the A/R group, maximum H₂O₂ efflux was no greater than for normoxia. Treatment with rotenone, an inhibitor of Complex I and reverse electron transport (RET), produced only a modest decrease in H₂O₂ efflux. This result indicates that RET, a major contributor to ROS bursts in mammalian mitochondria, is not stimulated by A/R in A. franciscana. Lack of aconitase inactivation, protein carbonyl accumulation, and lipid hydroperoxide production demonstrate that bouts of A/R do not cause significant oxidative damage in A. franciscana mitochondria. Finally, the capacity to downregulate Complex I activity through active-deactive conformations was tested and is not operative. These data collectively suggest that Complex I from A. franciscana may not possess the capacity for RET and the associated ROS surge.

Climate change is predicted to continue elevating regional sea surface temperatures (SST) and increase the frequency and severity of localized heating events, phenomena which may threaten the biodiversity, integrity, and function of tropical coral reef ecosystems. The primary objective of this study was to determine physiological and behavioral responses to elevated SST in a Hawaiian surgeonfish, the yellow tang, Zebrasoma flavescens. We assessed standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS), and swimming performance, as well as temperature preference (T_pref) in this ecologically and economically important coral reef fish. The Z. flavescens were acclimated to either the current maximum monthly summer SST around O'ahu, 27 °C, or an elevated SST, 31 °C. Acclimation temperature had no significant effect on SMR, MMR, AS, or swimming performance. Temperature preference was tested over a 24-hour period in an annular preference chamber with a gradient ranging from 24 to 34 °C. Our study found that Z. flavescens in both acclimation temperatures had a similar T_pref (median) of 27 °C with first and third quartiles of 25.7 to 29 °C. Analysis of relative use of available temperatures (compositional analysis) indicated a preference for the lowest available temperatures of 24 to 26 °C in both acclimation groups. These findings indicate that Z. flavescens can completely compensate AS and swimming ability to the elevated SST conditions, although T_pref remains near or below the current summer SST, suggesting other factors explain behavioral temperature preference.

Fish face a functional trade-off at the gills between minimizing ion movement and maximizing oxygen uptake - the osmorespiratory compromise, but the extent of this trade-off remains poorly understood in elasmobranchs. Using the Pacific dogfish shark, we assessed the impacts of progressive hypoxia in animals acclimated to 25, 30 and 36 ppt for 4 days at 12 °C. Plasma osmolality increased with water osmolality at 36 ppt (osmoconformation) and decreased at 25 ppt. Plasma urea decreased at 25 ppt, though to a lesser extent than plasma Cl^-, while plasma urea increased to a greater extent than plasma Cl^- at 36 ppt. In normoxia, oxygen consumption rate (MO₂) was elevated by 60% at 36 ppt, and ventilatory index (frequency x amplitude) was elevated by 70%, reflecting increases in both components of ventilation, but these parameters remained unchanged in sharks exposed to 25 ppt. During progressive hypoxia, MO₂ and ventilation exhibited different patterns at the three salinities, but in all three, MO₂ fell linearly below a water PO₂ of ~ 80 Torr (10.7 kPa), indicating oxyconformation. Under hypoxia (45 to 5 Torr; 6.0 to 0.7 kPa) MO₂ was the same at all salinities, while ventilatory amplitude was elevated at both 25 and 30 ppt. At 36 ppt, frequency decreased during hypoxia. Ventilatory index increased during hypoxia only at 30 ppt and not at the other salinities. From these data it is clear that dogfish sharks face an osmorespiratory compromise balancing the needs for urea retention against those of O₂ uptake.

Limited freshwater availability and increasing salinisation of inland water bodies pose significant challenges to sustainable aquaculture. In the context of climate change, the use of inland saline water (ISW) offers a practical alternative, enabling the expansion of aquaculture into water-scarce and non-arable regions. The combined effects of elevated temperature and salinity on genetically improved farmed tilapia fingerlings (initial weight: 2.73 ± 0.02 g) were evaluated after a 60-day experimental trial. Fish were distributed across six treatments in triplicates (n = 15/tank): Control (T_28.5 X FW), T1 (T_28.5 × 10), T2 (T_28.5 × 15), T3 (T_33.5 X FW), T4 (T_33.5 × 10), T5 (T_33.5 × 15 ), representing combinations of temperature (28.5-33.5 °C) and salinity (Freshwater, 10 ppt, or 15 ppt). Growth and physiological parameters were assessed after 60-day rearing in the designated treatments. Results revealed significant interactive effects on growth, with control achieving the highest final body weight (18.26 g) while T5 showed a 47% reduction. Hepatosomatic index showed no significant response to either factor, while the viscero-somatic index increased from 7.54% in control to 8.43% at 15 ppt. Haematological parameters increased with stressors, with T5 treatment showing a 32% increase in WBC count compared to the control. Serum protein profiles showed complex responses, with total protein in T_33.5 × 10 (10.82 g/dL) being higher than in the control (~ 2.7 times). Branchial LDH activity remained unchanged across treatments, while hepatic LDH activity in T_33.5 × 15 was 3-fold higher than that of the control. Aminotransferases (AST, ALT) and serum lipids also showed a similar trend, peaking at T5. Branchial NKA enzyme activity increased 5-fold in T5 compared to the control. Hepatic igf1 expression was downregulated with increasing salinity (70% reduction at 15 ppt) and temperature. These findings demonstrate that combined exposure to elevated temperature and salinity impairs growth and physiological alterations in GIFT tilapia, with implications for inland saline aquaculture under climate change scenarios.

Oxidative damage and inflammation are mechanisms proposed to contribute to physiological senescence. Variation in oxidative damage and inflammation may reflect differential allocation of resources to reproduction and survival, contributing to differences in species-typical longevity and resulting from distinct, evolved life-history strategies. To investigate the link between molecular processes and physiological senescence, we compared urinary biomarkers of oxidative stress (8-isoprostane and 8-OHdG) and inflammation (neopterin) in a cross-sectional sample of two species that differ in life-history schedules: the relatively fast-paced ring-tailed lemur (Lemur catta; n = 41; ages = 1-32 years) and slow-paced Coquerel's sifaka (Propithecus coquereli; n = 49; ages = 1-27 years). Consistent with a faster life-history pace, ring-tailed lemurs showed significantly higher average levels of DNA damage than did sifakas (8-OHdG: ring-tailed lemur mean: 18.6 ± 10.3 ng/mg Cr, sifaka mean 8.0 ± 9.0 ng/mg Cr, p = 0.001). Species differences in lipid damage and inflammatory biomarkers were not significant (8-isoprostane: ring-tailed lemur mean: 0.5 ± 0.3 ng/mg Cr, sifaka mean: 0.3 ± 0.2 ng/mg Cr, p = 0.11), although sifakas tended to show greater inflammation (neopterin: ring-tailed lemur mean: 0.01 ± 0.02 ng/mg Cr, sifaka mean: 0.02 ± 0.02 ng/mg Cr; p = 0.14), which may reflect health challenges faced by this species in captivity. Contrary to our predictions, neither species showed age-related change in either marker of oxidative stress. Thus, although lemurs appear not to experience an increase in the rate of oxidative damage incurred with age, we cannot exclude the possibility that accumulated damage contributes to aging. Neither lemur species exhibited age-related change in inflammation; if anything, contrary to our prediction, ring-tailed lemurs showed marginal declines in inflammation with age. This finding, consistent with a few recent studies of other non-human primates, suggests that lemurs avoid the phenomenon of "inflammaging" widely observed in humans.

East Pacific green turtles (Chelonia mydas) inhabit tropical and subtropical waters along the western coast of the Americas. This population uses the Gulf of California, Mexico, as a primary area for feeding and refuge, where they face various stressors. This study aimed to establish hematological reference intervals for healthy green turtles in this area (n = 326), as well as evaluate seasonal variations in blood parameters and compare values between healthy turtles and individuals affected by fibropapillomatosis (n = 25). Reference intervals for hematological analytes were estimated following the American Society for Veterinary Clinical Pathology guidelines. Seasons significantly influenced hemoglobin, hematocrit and heterophils, which were lower during the cold season, while monocytes and eosinophils were significantly higher. These variations were attributed to physiological effects of cooler water temperatures, shorter photoperiods, reduced food intake, and immune response to seasonal stressors during the colder months. Turtles with visible fibropapillomatosis tumors were mildly affected, with tumor sizes not exceeding 5-cm diameter (tumor score 1). While significant alterations were observed in some hematological analytes (i.e., lower hemoglobin and hematocrit, and higher WBC, lymphocytes and heterophil: lymphocyte ratio), these values remained within the reference intervals estimated for healthy turtles. Additionally, no abnormalities commonly associated with severe fibropapillomatosis were observed, suggesting minimal structural or functional damage at tumor score 1 stage. This baseline information will help evaluate intra-population trends, assess potential impacts from future ecosystem changes, and develop effective conservation strategies for this threatened population.

Hibernation is an adaptive strategy that conserves energy in response to environmental challenges. While mitochondrial proteomic adaptations are well-documented in deep hibernators, the proteomic changes underlying daily torpor remain less clear. We investigated mitochondrial proteomic adaptations in the liver of a daily hibernator, the Djungarian hamster (Phodopus sungorus), across different hibernation phases. Hamsters were maintained under long-day (summer) or short-day photoperiods (winter), to induce torpor. Livers from summer, torpor, and interbout euthermia phases were analyzed by liquid chromatography-mass spectrometry with labelled standards of mitochondrial energy metabolism proteins, resulting in accurate quantitative proteomics. Differential protein regulation was assessed using empirical Bayes models with false discovery rate correction. Increased abundance of fatty acid oxidation enzymes during hibernation indicates a seasonal metabolic shift toward lipid utilization, similar to deep hibernators. Additionally, torpor featured elevated complex II subunits and tricarboxylic acid cycle enzymes representing evolutionary adaptations specific to daily torpor, likely to cater higher energy demands necessary to maintain torpid body temperature above 15 °C in near-freezing ambient temperatures. This represents evolutionary adaptations specific to daily torpor. Increased levels of the mitochondrial uncoupling-related solute carrier family 25 member 5 (SLC25A5) may be responsible for both thermogenesis and limiting production of reactive oxygen species. Furthermore, the selective upregulation of SOD2 during torpor underscores its critical role in mitigating reactive oxygen species accumulation during metabolic transitions. In summary, daily torpor exhibits unique mitochondrial proteomic adaptations that distinguish it from deep torpor, which may be necessary to enable torpor at body temperatures well above the ambient temperature.