Aging produces significant changes in the human endocrine system. This study was designed todetermine if elderly and younger individuals differ in various endocrine measures before and after ultraendurance stress. Sixteen young and 19 older subjects competing in a world championship triathlon had blood samples acquired for 13 hormones before, immediately after the event, and 18 hours into recovery. Following the triathlon, almost every hormone level increased. Significantly higher basal circulating levels ofdihydroepiandrosterone sulfate (DHEA-S) and thyroid stimulating hormone (TSH) were found in 20-year-old individuals,whereas higher levels of norepinephrine (NEPI) and sex hormone binding globulin (SHBG) were found in the 50- to74-year-old group. Older subjects had lower postexercise levels of EPI, DHEA-S, GH, and PRL and higher postexerciselevels of estradiol than younger individuals. Similarity in pre- and postrace weights as well as Hgb and Hct levels suggested that dehydration, while present, did not significantly contribute to the endocrine changes. Utraendurance stress produced dramatic increases in all but one of the hormones evaluated. Whether frequent exercise can alter the endocrine changes that occur with aging cannot be answered by this study. It is clear,however, that when comparisons are made with young active individuals, frequent exercise does not eliminate the differences in basal concentrations of TSH, DHEA-S, SHBG, and NEPI or exercise-induced release of estradiol, GH,and PRL that occur with aging.
The objective of this study was to address the cellular and psychological mechanisms underlying previously observed changes in natural killer (NK) cell cytotoxicity associated with chronic stress. We compared 28 current and former spousal caregivers of patients with Alzheimer's disease (AD) and 29 control subjects. NK cells were enriched (E-NK) using a 4-step procedure that resulted in a cell preparation consisting of 88.2% NK cells. These cells were then incubated with either recombinant interferon-gamma (rIFN-gamma) or recombinant interleukin-2 (rIL-2) for 65 hours. Although an average of over 3 years had elapsed since the death of the patient with AD for the former caregivers, current and former caregivers did not differ in the E-NK cell responses to rIFN-gamma and rIL-2. However, the E-NK cell response for the combined caregiver group was significantly suppressed compared with controls, which is consistent with a previous report from our laboratory. Higher E-NK cell responses to each cytokine were associated with heightened levels of positive emotional and tangible social support, independent of levels of depression. Preliminary data suggest that defects of NK cell function in response to rIFN-gamma and rIL-2 as a consequence of caregiver stress may be independent of non-NK cells. Finally, our data are consistent with other studies regarding the role of social support in immune modulation.
