Effects of a Longitudinal Training Program on Responses to Exercise in Overweight Men

Objective: The aim of this study was to determine how training modifies metabolic responses and lipid oxidation in overweight young male subjects. Research Methods and Procedures: Eleven overweight subjects were selected for a 4‐month endurance training program. Before and after the training period, they cycled for 60 minutes at 50% of their Vo ₂max after an overnight fast or 3 hours after eating a standardized meal. Various metabolic and endocrine parameters, and respiratory exchange ratio values were evaluated. Results: Exercise‐induced plasma norepinephrine concentration increases were similar before and after training in fasted or fed conditions. After food intake, exercise promoted a decrease in plasma glucose and a higher increase in epinephrine than in fasting conditions. The increase in epinephrine after the meal was more marked after training (264 ± 32 vs. 195 ± 35 pg/mL). Training lowered the resting plasma nonesterified fatty acids. During exercise, changes in glycerol were similar to those found before training. Lipid oxidation during exercise was higher in fasting than in fed conditions (15.5 ± 1.4 vs. 22.3 ± 1.7 g/h). Training did not significantly increase fat oxidation when exercise was performed in fed conditions, but it did in fasting conditions (18.6 ± 1.4 vs. 27.2 ± 1.8 g/h). Discussion: Endurance training decreased plasma nonesterified fatty acids, cholesterol, and insulin concentrations. Training increased lipid oxidation during exercise, in fasting conditions, and not when exercise was performed after the meal. During exercise in overweight subjects, the fasting condition seems more suited to oxidizing fat and maintaining glucose homeostasis than a 3‐hour wait after a standard meal.     

Indications de la recherche des anticorps anti-spermatozoïdes

The clinical significance of antisperm antibodies (ASA) is highly controversial. A significant percentage of infertile men and women present immunity to spermatozoa, suggesting that ASA may interfere with the fertilizing capacity. ASA can act negatively on sperm parameters, sperm-cervical mucus interaction, gamete fusion and possibly also on the first step of embryonic development. ASA are present in approximately 2.8% to 26% of the male population and 0.2% to 1.6% of women. The pathogenesis of immunity to spermatozoa had not been fully elucidated: breakdown of normal protective mechanisms, i.e. blood-testis barrier, or epithelial barrier in women, and other mechanisms of immunological sperm tolerance, such as regulation of suppressor T lymphocytes. The indication for antisperm antibody testing is based on clinical and laboratory findings of infertile patients. In men, indictions for ASA testing include a history of genital disease, surgery for genital abnormalities, vasectomy, obstruction or injuries of the male genital tract, infection of accessory glands, long-standing infertility, alteration of semen parameters (agglutination, motility), mucus penetration, and reduced fertilizing capacity in IVF. In many cases, no etiological cause of autoimmunity is found and a genetic predisposition has been suggested. A majority of women do not develop antisperm antibodies, despite repeated contact with spermatozoa during their sexual life. Upper genital tract infection is the main cause of isoimmunization in females, although sexual practices, endometriosis, surgery for cervical neoplasia, recurrent spontaneous abortion and long-term infertility may also be involved. Sperm-cervical mucus impairment is the most obvious effect of immunization in women associated with IVF failure. Autoantibodies are frequently associated with antisperm antibodies. One of the consequences of the success of ICSI has been a decreased research effort to further the understanding of the origin and relevance of antisperm antibodies and specific antibody-antigen interactions. A better understanding of the natural history of immunological infertility would be useful for patient conseiling and to develop the most effective, efficient and safest management strategies. Such data could also be useful for the development of new tests and immunological methods of male contraception.     

Cortisol and behavioral responses to enrichment in military working dogs

Our objective was to compare the effects of two schedules of enrichment exposure, a distributed (high frequency) and regular regime versus a mass (low frequency) and irregular regime, on the cortisol and behavioral responses of 14 kennelled military working dogs. The enrichment experiences were exercise coupled with human contact. Both groups of dogs were exposed to approximately the same total amount of enrichment per week for a total of 7 weeks. The distributed and regular regime (DRR) furnished enrichment for 20-min intervals three to four times a day every weekday; the mass and irregular regime (MIR) randomly furnished enrichment for 16 or 24 continuous hours 1 day out of 5. Our data show that: (1) cortisol concentrations of DRR dogs significantly decreased between the first and the last week of observations; this was not the case in MIR dogs; (2) at the 7th week DRR dogs had lower cortisol concentrations than did MIR dogs; (3) all dogs in each group exhibited stereotypies. Our results suggest that MIR dogs underwent a decline in welfare throughout the experiment, whereas DRR dogs appeared to undergo a period of acute stress at the beginning of their training that resolved over 7 weeks. This study suggests that the welfare of kennelled dogs, particularly military working dogs, is affected among other factors by schedules of exercise and contact with people.     

Steady-state levels of imported tRNAs in Chlamydomonas mitochondria are correlated with both cytosolic and mitochondrial codon usages

The mitochondrial genome of Chlamydomonas reinhardtii only encodes three expressed tRNA genes, thus most mitochondrial tRNAs are likely imported. The sharing of tRNAs between chloroplasts and mitochondria has been speculated in this organism. We first demonstrate that no plastidial tRNA is present in mitochondria and that the mitochondrial translation mainly relies on the import of nucleus-encoded tRNA species. Then, using northern analysis, we show that the extent of mitochondrial localization for the 49 tRNA isoacceptor families encoded by the C. reinhardtii nuclear genome is highly variable. Until now the reasons for such variability were unknown. By comparing cytosolic and mitochondrial codon usage with the sub-cellular distribution of tRNAs, we provide unprecedented evidence that the steady-state level of a mitochondrial tRNA is linked not only to the frequency of the cognate codon in mitochondria but also to its frequency in the cytosol, then allowing optimal mitochondrial translation.     

Dynamics of RecA filaments on single-stranded DNA

RecA, the key protein in homologous recombination, performs its actions as a helical filament on single-stranded DNA (ssDNA). ATP hydrolysis makes the RecA–ssDNA filament dynamic and is essential for successful recombination. RecA has been studied extensively by single-molecule techniques on double-stranded DNA (dsDNA). Here we directly probe the structure and kinetics of RecA interaction with its biologically most relevant substrate, long ssDNA molecules. We find that RecA ATPase activity is required for the formation of long continuous filaments on ssDNA. These filaments both nucleate and extend with a multimeric unit as indicated by the Hill coefficient of 5.4 for filament nucleation. Disassembly rates of RecA from ssDNA decrease with applied stretching force, corresponding to a mechanism where protein-induced stretching of the ssDNA aids in the disassembly. Finally, we show that RecA–ssDNA filaments can reversibly interconvert between an extended, ATP-bound, and a compressed, ADP-bound state. Taken together, our results demonstrate that ATP hydrolysis has a major influence on the structure and state of RecA filaments on ssDNA.     

Unsaturated fatty acid regulation of cytochrome P450 expression via a CAR-dependent pathway

The liver is responsible for key metabolic functions, including control of normal homoeostasis in response to diet and xenobiotic metabolism/detoxification. We have shown previously that inactivation of the hepatic cytochrome P450 system through conditional deletion of POR (P450 oxidoreductase) induces hepatic steatosis, liver growth and P450 expression. We have exploited a new conditional model of POR deletion to investigate the mechanism underlying these changes. We demonstrate that P450 induction, liver growth and hepatic triacylglycerol (triglyceride) homoeostasis are intimately linked and provide evidence that the observed phenotypes result from hepatic accumulation of unsaturated fatty acids, which mediate these phenotypes by activation of the nuclear receptor CAR (constitutive androstane receptor) and, to a lesser degree, PXR (pregnane X receptor). To our knowledge this is the first direct evidence that P450s play a major role in controlling unsaturated fatty acid homoeostasis via CAR. The regulation of P450s involved in xenobiotic metabolism by this mechanism has potentially significant implications for individual responses to drugs and environmental chemicals.     

Exploiting flavour preferences of common marmosets to increase palatability of a dry pellet diet

Although commercially available complete diets exist for common marmosets, the animals’ consumption of these diets (available in dry pellet form) is typically very low. Increasing consumption of the pellet diet could have positive consequences for the welfare of the marmosets as the pellets are designed specifically to meet their full nutritional requirements, and therefore an increase in intake should help to ensure that they take in an appropriate balance of nutrients. We carried out a series of studies targeted towards improving the palatability, and hence increasing the intake, of a complete dry pellet diet for marmosets. In Study 1 we attempted to determine which of a wide range of flavours appeared to be preferred by the marmosets. In Study 2 we tested the marmosets’ preferences for a smaller number of highly preferred flavours (as determined in Study 1) when actually added to the dry pellet diet in a series of paired preference tests. Finally, in Study 3 we tested whether adding the most highly preferred flavours (as determined in Study 2) to the dry pellet diet would in fact increase consumption of these pellets in comparison with unflavoured pellets. Despite finding strong and consistent preferences for particular flavours amongst the marmosets, we found that adding these to the pellets did not significantly increase consumption. Reasons for this are discussed, along with other potential modifications which might prove more successful in increasing consumption of pellet diets for marmosets.     

Desirable plant root traits for protecting natural and engineered slopes against landslides

Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference ‘Ground Bio- and Eco-engineering: The Use of Vegetation to Improve Slope Stability—ICGBE2’ held at Beijing, China, 14–18 July 2008. Several papers from this conference are published in this edition of Plant and Soil.