Age-related changes in metabolic parameters of nonhuman primates.

Some physiological measures change with age, but the existence of age-related disorders such as type 2 diabetes raises questions about which patterns reflect progressive pathology and which are manifestations of aging. Here we report a retrospective investigation of age-related physiological changes in rhesus monkeys that developed diabetes (D group, n = 65) or exhibited healthy aging (N group, n = 88). Data were available on clinical chemistries, hematology, glucose tolerance, and insulin sensitivity based on oral and intravenous glucose tolerance tests and euglycemic, hyperinsulinemic clamp assessments. Individuals contributed data for an average of 7.6 years, when they were between 5 and 30 years of age. Only glucose disappearance rate, insulin sensitivity rate, and high density lipoprotein levels changed significantly with age in the nondiabetic group. In the diabetic group, significant decreases in glucose tolerance were evident by middle age (age 14 y), and fasting insulin first increased before diabetes was diagnosed, and then declined with advancing age.

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.