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

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. 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. 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. 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.