The circadian rhythm in plasma ACTH and plasma cortisol was determined by radioimmunoassay in 324 diurnally active elderly subjects 57 to 95 years of age. The body mass index (BMI) was obtained and the circadian means of ACTH and cortisol in subjects with a BMI below 30 (202 subjects) were compared with obese subjects (122 Subjects) with a BMI of 30 and above.
Results: The obese subjects showed significantly lower circadian mean in ACTH but not lower circadian means in plasma cortisol. The ACTH in obese subjects was 17.9 ± 1.4 as compared to 27.5 ± 2.2 in the non- obese subjects (F = 9.784, p = 0.0019), while cortisol was 9.1 ± 0.2 and 9.6 ± 0.2 (F = 3.061, p = 0.0811) respectively. The ACTH/Cortisol ratio in the obese was 2.03 ± 0.18 as compared to 3.70 ± 0.34 in the non-obese subjects (F = 8.360, p = 0.0041). This change in the ACTH/Cortisol ratio suggests an increased sensitivity of the adrenal in obese subjects to endogenous ACTH which may be of interest for the pathogenesis of this disorder.