Dietary arachidonic acid improves age-related excessive enhancement of the stress response

OBJECTIVE

The aim of this study is to understand whether the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to stress increases excessively with aging in senescence-accelerated mice-prone 10 (SAMP10) and to investigate the role of arachidonic acid (ARA) in this process.

MATERIALS AND METHODS

The area under the curve of CORT concentration (CORT-AUC), an index of the HPA axis responsiveness to stress, was assessed in SAMP10 subjected to a 30-minute restraint stress up to 120 minutes after the restraint stress onset. Furthermore, the HPA axis responsiveness was evaluated in aged SAMP10 fed 0.4% ARA-containing diet (ARA group) or control diet (CON group) for 4 weeks. Three weeks later, these mice were divided into a group with a 30-minute restraint stress (CON-S or ARA-S group) and a group without restraint stress (CON-NS or ARA-NS group). Hippocampi were collected after stress release and fatty acid and glucocorticoid receptor (GR) protein levels were evaluated in the nucleus and cytosol.

RESULTS

The CORT-AUC of aged SAMP10 was 21% significantly higher than that of young SAMP10. In the ARA group, hippocampal ARA was 0.5% significantly higher than that in the CON group. CORT-AUC in the ARA group was 24% significantly lower than that in the CON group. The ratio of GR protein levels in the nucleus and cytosol in the ARA-S group was 1.72 times significantly higher than that in the ARA-NS group but no difference was observed between the CON-S and CON-NS groups.

CONCLUSIONS

Dietary ARA seems to suppress age-related excessive enhancement of the HPA axis responsiveness via attenuation of age-related decline in hippocampal GR translocation into the nucleus after stress loading, which may contribute to an improvement of mental health.

Effect of Temperature and Oxygen on the Strength of Elastomers

1. A linear relationship has been found to hold for SBR vulcanizates between the logarithm of the rate of steady tearing and the logarithm of air pressure, over the range 10 Pa to 100 kPa. The slope varied from 0.08 for a C-C crosslinked material to 0.18 for a polysulfide-crosslinked material. Similar effects of air pressure were found in the rate of crack propagation under intermittent loading. They are attributed to attack of oxygen (in air) on highly stressed bonds, either sulfidic or hydrocarbon. 2. Approximately linear relationships were found to hold between the logarithm of the rate of steady tearing and the reciprocal of test temperature for temperatures between 25°C and 130°C. Apparent activation energies were deduced from the slopes, of 135 kJ/mole for a polysulfide-crosslinked SBR compound, 105 kJ/mole for a C-C crosslinked SBR compound, and 85 kJ/mole for a sulfur vulcanizate of BR. For SBR, these values were independent of air pressure. 3. These activation energies are far too large to be accounted for by changes in segmental mobility (and hence in internal energy dissipation) with temperature, for simple viscoelastic materials at temperatures far above Tg. The discrepancies are attributed to a second temperature-dependent factor. It is suggested that the threshold tear strength T0, i.e., the strength under nondissipative conditions, is itself temperature dependent. 4. Estimates of the changes in T0 with temperature have been obtained from the observed discrepancies in temperature dependence of tear strength. They correspond to a decrease from about 100–250 J/m2 at 25°C to about 50 J/m2 at 130°C. These changes in T0 may reflect the stress-activated rupture of thermally-sensitive bonds.