Behavioural reactions of desert bighorn sheep to avian scavengers

I report previously undocumented encounters between avian scavengers and desert bighorn sheep ( Ovis canadensis nelsoni ). These encounters are of interest because they occurred only during the nursery season when lamb mortality was high. Desert bighorn sheep responded to the presence of avian scavengers with typical anti-predator behaviours, which may indicate that avian scavengers are potential predators or that desert bighorn sheep are unable to distinguish between avian scavengers and avian predators.     

Metabolic consequences of hard work

When an animal has to meet increased demands on its working capacity, for example, for thermoregulation or parental care, two strategies are available. The animal can reallocate energy from costly maintenance processes - such as immunological defence or DNA repair systems (compensation hypothesis) - or it may try to increase the rate of energy intake or efficiency of digestion by increasing the size of the alimentary tract (increased-intake hypothesis). By manipulating brood size, I affected parental effort among marsh tits (Parus palustris) as demonstrated by a significant increase in parental feeding rate with experimental brood size. Basal metabolic rate (BMR) increased both with manipulated brood size and individual feeding rate, supporting the predictions from the increased-intake hypothesis. Furthermore, I found a direct positive relation between BMR and energy expenditure, measured with the help of the doubly labelled water technique. The cost of achieving a higher working capacity is substantial since BMR increases more quickly than the surplus energy available for work. Since the cost of a high sustained workload was not primarily dependent on a reallocation of energy away from maintenance, such a cost should be searched for among the detrimental effects of a high metabolic rate per se, for example, an increased oxidative damage to DNA, proteins and lipids.     

Metabolic rate and jump performance in seven species of desert fleas

We hypothesized that sexual and interspecific differences in jumping performance of fleas found in our previous study are correlated with differences in resting metabolic rate (RMR) between sexes and among species. To test this hypothesis, we measured RMR of seven flea species (Xenopsylla conformis mycerini, Xenopsylla ramesis, Xenopsylla dipodilli, Parapulex chephrenis, Synosternus cleopatrae pyramidis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis). We compared RMR between sexes and among species and examined whether there is intra- and interspecific correlation between RMR and jumping ability. Both mass-specific and mass-independent RMR were the highest in female S. t. medialis, whereas mass-specific RMR was the lowest in male X. dipodilli and mass-independent RMR was the lowest in three Xenopsylla species and P. chephrenis. Mass-specific and mass-independent RMR were significantly higher in females than in males in all fleas except S. t. medialis. Differences in jumping ability between males and females were found to be correlated with sexual differences in mass-specific or mass-independent RMR. Interspecific comparison showed that the length of jump in both male and female fleas was strongly affected by their mass-specific and mass-independent RMR.     

Putting bioactivation reactions to work: Targeting antioxidants to mitochondria

The goal of this research was to test the hypothesis that bioactivation reactions could be exploited to deliver and activate mitochondria-targeted antioxidant prodrugs. The concept that bioactivation reactions could be used for prodrug delivery and activation has received little attention. Most bioactivation reactions result in the conversion of the parent drug to a reactive electrophilic metabolite, but bioactivating enzymes that catalyze elimination or hydrolytic reactions may offer potential for targeted drug delivery. Because mitochondria are the major cellular source of reactive oxygen species, there is much interest in targeting antioxidants to mitochondria. Previous studies showed that the mitochondrial fatty acid β-oxidation pathway biotransforms a range of xenobiotic alkanoates, including ω-(phenyl)alkanoates and ω-(phenoxy)alkanoates. 5,6-Dichloro-4-thia-5-hexenoate, the desamino analog of S-(1,2-dichlorovinyl)-l-cysteine, is biotransformed by the fatty acid β-oxidation pathway. Hence, the prodrugs ω-(phenoxy)alkanoates, 3-(phenoxy)acrylates, and ω-(1-methyl-1H-imidazol-2-ylthio)alkanoates were expected to undergo biotransformation by the mitochondrial β-oxidation pathway to release phenolic antioxidants and the antioxidant methimazole (Roser et al., Bioorg. Med. Chem. 18 (2010) 1441-1448). The rates of biotransformation of ω-(phenoxy)alkanoates varied with the structure, and bulky substituents on the phenoxy moiety reduced rates of biotransformation; this was attributed to substrate limitations imposed by the medium-chain acyl-CoA dehydrogenase. Hence, 3-(2,6-dimethylphenoxy)acrylate was prepared; it was expected that, after conversion to its CoA thioester, 3-(2,6-dimethylphenoxy)acryloyl-CoA would be a substrate for enoyl-CoA hydratase. This expectation was correct: 3-(2,6-dimethylphenoxy)acrylate was an excellent substrate. ω-(1-Methyl-1H-imidazol-2-ylthio)alkanoates were also good substrates for the β-oxidation pathway. Significantly, 3-(2,6-dimethylphenoxy)propanoate, 3-(2,6-dimethylphenoxy)acrylate, and 3-(1-methyl-1H-imidazol-2-ylthio)propanoate were cytoprotective in a hypoxia-reoxygenation model in rat cardiomyocytes. These results demonstrate the feasibility of exploiting bioactivation reactions for targeted drug delivery.     

Resources and the flexible allocation of work in the desert ant, Aphaenogaster cockerelli

Summary: Social insect colonies can respond to changes in resource availability by altering their foraging behavior. Colonies of the desert ant, Aphaenogaster cockerelli, responded to experimental changes in the distribution and type of available resources by adjusting the numbers of ants engaged in foraging and other tasks outside the nest, and by adjusting the temporal patterns of these activities. Colonies foraged more intensely for protein resources than for seed resources, and for high-density resources more than for low-density resources. This flexible allocation and resource use may promote coexistence with interspecific competitors such as ants in the genus Myrmecocystus.     

Metabolic adaptations of the gerbil, Gerbillus campestris, to a desert climate. Comparison with white mice

Metabolic rate of gerbils was lower than that of mice (35%). We tried to assess the part played by brown adipose tissue in this low level. Mitochondrial respiration (state 4), protein content and cytochrome-oxidase activity of interscapular BAT mitochondria were very low in gerbils compared to mice, whereas in liver and muscle these parameters were not significantly different. Like in fasting animals, the low level of basal energy expenditure of gerbils may be ascribed to low activity of BAT.     

Metabolic and work efficiencies during exercise in Andean natives

Maximum O2 and CO2 fluxes during exercise were less perturbed by hypoxia in Quechua natives from the Andes than in lowlanders. In exploring how this was achieved, we found that, for a given work rate, Quechua highlanders at 4,200 m accumulated substantially less lactate than lowlanders at sea level normoxia (approximately 5-7 vs. 10-14 mM) despite hypobaric hypoxia. This phenomenon, known as the lactate paradox, was entirely refractory to normoxia-hypoxia transitions. In lowlanders, the lactate paradox is an acclimation; however, in Quechuas, the lactate paradox is an expression of metabolic organization that did not deacclimate, at least over the 6-wk period of our study. Thus it was concluded that this metabolic organization is a developmentally or genetically fixed characteristic selected because of the efficiency advantage of aerobic metabolism (high ATP yield per mol of substrate metabolized) compared with anaerobic glycolysis. Measurements of respiratory quotient indicated preferential use of carbohydrate as fuel for muscle work, which is also advantageous in hypoxia because it maximizes the yield of ATP per mol of O2 consumed. Finally, minimizing the cost of muscle work was also reflected in energetic efficiency as classically defined (power output per metabolic power input); this was evident at all work rates but was most pronounced at submaximal work rates (efficiency approximately 1.5 times higher than in lowlander athletes). Because plots of power output vs. metabolic power input did not extrapolate to the origin, it was concluded 1) that exercise in both groups sustained a significant ATP expenditure not convertible to mechanical work but 2) that this expenditure was downregulated in Andean natives by thus far unexplained mechanisms.     

Metabolic reactions in sensory and motor neurons after exposure to various physical factors]

A course of radiation of biologically active points of the guinea pig lumbosacral area has been performed by means of focused frequency-modulated and a continuous beam of the helium-neon laser, having various power density, as well as by means of an impulsive magnetic field. A comparative histoenzymatic analysis of sensitive neurons of the lumbar spinal nodes and of the caudal-mesenteric motor neurons has been carried out. The response of the metabolic processes in the sensitive neurons depends not so much on the type of action, as on adequacy of the parameters applied. The power density, frequency of impulse generation and time of application are important for characterization of the adequacy of the laser radiation. Peculiarities of the metabolic reactions in the sensitive and sympathetic neurons in response to the actions studied are discussed.     

Metabolic control reactions of the intact urinary bladder of the toad

Metabolic control reactions have been studied in the intact toad bladder by means of fluorescence spectrophotometric measurement of reduced pyridine nucleotide and by measurement of respiration with the platinum electrode. substrates such as pyruvate and succinate lead to prompt increases in reduction level of pyridine nucleotide with only slight acceleration of respiration. major metabolic control is exerted by adp, which depletes the intact bladder of reduced pyridine nucleotide and accelerates respiration. respiratory control ratios, as for isolated mitochondria, depend upon the substrate being metabolized. a significant fraction of added adp appears to gain entry into the intact toad bladder and is converted to atp, anaerobiosis and amobarbital lead to increased levels of reduction of pyridine nucleotide. the spectroscopic and metabolic properties of the reduced pyridine nucleotide being studied identify it with that fraction of dpnh which is bound at one of the energy conservation sites linking phosphorylation reactions with electron transfer.     

Metabolic syndrome components: Is there a difference according to exposure to night work?

ABSTRACT

The aim of this study was to compare metabolic aspects potentially associated with metabolic syndrome (MetS), in addition to serum leptin levels and sleep, according to exposure to night work among nursing staff. A cross-sectional study involving 60 nursing staff was conducted. Sociodemographic, sleep (Karolinska Sleep Questionnaire), physical activity (International Physical Activity Questionnaire), and nutrition data (16-Food Intake Questionnaire) were collected. Body measurements and blood pressure were taken and blood collected to determine glycemia, total cholesterol and portions of low-density lipoprotein and high-density lipoprotein and triglycerides, and leptin levels. The sample was divided into three groups according to exposure to night work (nonexposed, currently exposed, past exposure). Furthermore, to evaluate the relationship between exposure time and prevalence of MetS, the night-exposed groups (past and current) were divided according to time exposed to night shifts (<10 years and ≥10 years). Mean age of participants was 39.8 ± 10.5 years. The groups were homogenous with regard to sociodemographic characteristics, physical activity, dietary patterns, and health aspects. The prevalence of MetS in the population studied was 32%, above the rate for the general population. However, there were no significant differences among the groups. In addition, a higher proportion of participants with hypertriglyceridemia and diastolic arterial hypertension was observed in the currently exposed group. The currently exposed group also reported less sleep and higher sleep debt than the other groups on workdays. Although no differences were observed among the groups regarding MetS, the currently exposed group had more sleep disturbances than the others, and a higher prevalence of two out of three risk factors for the MetS diagnosis.     

Metabolic support of moderate activity differs from patterns seen after extreme behavior in the desert iguana Dipsosaurus dorsalis

This study examined glucose and lactate metabolism in an iguanid lizard, Dipsosaurus dorsalis, during rest and after activity patterned on field behavior (15 s of running at 1 m/s). Metabolite oxidation and incorporation into glycogen by the whole animal, the liver, and oxidative and glycolytic muscle fibers were measured using (14)C- and (13)C-labeled compounds. Results showed that lactate metabolism is more responsive to changes that occurred between rest and recovery, whereas glucose appears to play a more steady state role. After activity, lactate oxidation produced 57 times as much ATP during 1 h of recovery than did glucose oxidation. However, lactate oxidation rates were elevated for only 30 min after activity, while glucose oxidation remained elevated beyond 1 h. Lactate was the primary source for glycogen synthesis during recovery, and glucose was the main glycogenic substrate during rest. This study supports previous research showing that brief activity in D. dorsalis is primarily supported by glycolysis and phosphocreatine breakdown, but it also suggests that there may be less of a reliance on glycolysis and a greater reliance on phosphocreatine than previously shown. The findings presented here indicate that the metabolic consequences of the behaviorally relevant activity studied are less severe than has been suggested by studies using more extreme activity patterns.     

Metabolic reactions responsible for glucose stimulation of alkaline phosphatase in Vibrio cholerae

Alkaline phosphatase activity in Vibrio cholerae strain 569B grown in low-phosphate medium was stimulated if glucose or glycerol was used as the carbon source. No such stimulation was observed, however, if tricarboxylic acid cycle intermediates like succinate or citrate were used. Experiments using specific enzyme inhibitors strongly indicated that the metabolic reactions of the glycolytic pathway from glyceraldehyde 3-phosphate to 2-phosphoglycerate play a key role in the stimulation process.