hypothalamicpituitaryadrenal axis and sympathetic nervous system activities in pima indians and caucasians it has been proposed that both hypercortisolism and low sympathetic nervous system sns activity contribute to obesity because glucocorticoids inhibit sns activity we hypothesized that hypercortisolism and low sns activity may be found in association in pima indians a population with a high prevalence of obesity we therefore measured indices of hypothalamicpituitaryadrenal hpa axis and sns activities in 39 nondiabetic men 20 pimas age 305 years weight 9426 kg 358 body fat mean sd and 19 caucasians 339 years 9123 kg 2811 body fat hpa axis activity was assessed by measurements of morning fasting plasma corticotropin acth and cortisol concentrations and 24hour urinary free cortisol ufc excretion sns activity was assessed as muscle sympathetic nerve activity msna by microneurography and by measurement of catecholamines fasting plasma concentration and 24hour urinary excretion plasma acth and cortisol and ufc were similar in pimas and caucasians msna was positively correlated with percent body fat r 49 p 002 and was lower in pimas compared with caucasians after adjustment for percent body fat 249 v 3110 burstsmin p 04 we conclude that pima indians a population with a high prevalence of obesity have lower sns activity but normal hpa axis activity compared with caucasians