Abstract # 183:

Scheduled for Saturday, June 23, 2007 08:45 AM-09:00 AM: Session 17 (North Main Hall E) Oral Presentation

Specific Gravity and Creatinine as Corrections for Urinary Cortisol

B. C. White, C. Brownson and A. Lally
Centre College, Psychobiology Program, 600 W. Walnut St., Danville, Kentucky 40422, USA
     The stress hormone, cortisol, can be measured in urine and other body fluids. In captive animals, urine is often available and yields measurable quantities of cortisol, but it is subject to variation in the hydration of the animal. This is usually corrected by expressing cortisol relative to creatinine concentration, which is influenced by gender, muscle mass, and activity. In the present study, we compared creatinine and specific gravity as corrections for urinary dilution as human subjects (Homo sapiens)¬†processed a large water load. Ten subjects voided completely and then consumed water (15ml/kg). At twenty minute intervals, subjects provided complete voids and saliva samples for 80 minutes. From the urine samples, we measured specific gravity (refractometer), cortisol (radioimmunoassay), and creatinine (colorimetric assay). Saliva samples were assayed for cortisol. As expected, salivary cortisol did not change [F(4,36)=2.45, p>0.05] but urinary cortisol declined dramatically as the urine became very dilute [F(4,36)=33.52, p<0.05]. Urinary cortisol corrected with specific gravity did not change significantly [F(4,36)=1.67, p>0.05], while creatinine corrected cortisol increased significantly as the urine became dilute [F(4,36)=4.21, p<0.05]. The specific gravity-corrected cortisol more closely resembled the salivary cortisol. We conclude that the specific gravity correction is at least as accurate as creatinine in approximating the unbound serum concentration as reflected in saliva. Creatinine and specific gravity corrections yield similar results in showing circadian cortisol variation in Lagothrix lagothricha and Gorilla gorilla.