Age-related levels of urinary free cortisol in the tree shrew

There are still controversies concerning the effect of aging on the basal glucocorticoid concentration in mammals, including humans. Some studies reported an elevated glucocorticoid concentration in older subjects, while other reports showed no increases with age. These discrepancies may be caused by different experimental designs, gender differences, or varying sampling time points. The bulk of animal studies reporting increases of glucocorticoids with age were performed in rats. The present study was designed to investigate the impact of age on adrenocortical activity in a non-rodent mammalian species, tree shrews (Tupaia belangeri). We analyzed the basal urinary free cortisol concentration in the morning urine of male tree shrews in different age groups. Immediately after birth, a large variation in basal urinary free cortisol concentration (10–818 pg/μmol crea) has been observed. Between 21–40 day of age, the urinary cortisol concentration was low (32.7 ± 5.6 pg/μmol crea) and increased steadily during puberty until adulthood (201–500 days; 161.8 ± 15.1 pg/μmol crea). Thereafter, no further rise in basal urinary free cortisol concentration was found with increasing age and after reaching senescence (7–8 years).