Background: High urine volume enhances urinary free cortisol (UFF) and cortisone (UFE) excretion rates in normal-weight adults and children. Renal excretion rates of glucocorticoids (GC) and their metabolites are frequently altered in obesity. The aim of the present study was to investigate whether UFF and UFE excretion is also affected by urine volume in severely obese subjects.
Experimental: In 24-h urine samples of 59 extremely obese subjects (mean BMI 45.3+/-8.9 kg/m(2)) and 20 healthy lean subjects (BMI 22.1+/-1.8 kg/m(2)), UFF and UFE, tetrahydrocortisol (THF), 5alpha-tetrahydrocortisol (5alpha-THF), and tetrahydrocortisone (THE) were quantified by RIA. The sum of THF, 5alpha-THF, and THE (GC3), the three major GC metabolites, reflects daily cortisol secretion. 11beta-Hydroxysteroid dehydrogenase type 2 (11beta-HSD2) activity was assessed by the ratio UFE/UFF. Daily GC excretion rates were corrected for urine creatinine and adjusted for gender and body weight.
Results: In extremely obese subjects, urine volume was significantly associated with creatinine-corrected UFE and 11beta-HSD2 activity after adjustment for gender and BMI (r=0.47, p=0.0002 and r=0.31, p=0.02, respectively). However, urine volume was not associated with creatinine-corrected UFF and GC3 (p=0.4 and p=0.6, respectively). In lean controls, urine volume was significantly associated with creatinine-corrected UFE and UFF (r=0.58, p=0.01 and r=0.55, p=0.02, respectively), whereas urine volume was not associated with 11beta-HSD2 activity after appropriate adjustment (p=0.3).
Conclusions: In severe obesity, in contrast to normal weight, renal excretion of UFE, but not of UFF is affected by fluid intake. This discrepancy may be due to the increased renal 11beta-HSD2 activity in obesity.