Age-related changes in fasting plasma cortisol in rhesus monkeys: implications of individual differences for pathological consequences.

Elevated cortisol may damage receptor neurons involved in responses to stress, leading to progressive metabolic dysregulation and age-related increases in cortisol; however, documentation of rising cortisol with age in humans has been inconsistent. Here we report fasting cortisol values from rhesus monkeys maintained for obesity, diabetes, and aging research. A modest correlation (r =.20) between age and cortisol was found for 138 rhesus monkeys (aged 4-40 years) and (r =.16) for 30 males for whom at least 10 years of longitudinal data were available. Subgroups of ad libitum-fed and weight-stabilized animals also exhibited significant positive relationships between age and cortisol (r =.14-.37). Individual regression analyses revealed both significant increases (r =.29-.85) and decreases (r = -.47 to -.66) in cortisol relative to age. Unexpectedly, significant age-related increases occurred in 77% of healthy primates, but only 33% of diabetic primates, while significant declines occurred only in diabetics.