EFFECT OF GRAPEFRUIT JUICE ON URINARY 6-BETA-HYDROXYCORTISOL CORTISOLEXCRETION/

1. The aim of the present study was to evaluate the effect of grapefru it juice on urinary 6 beta-hydroxycortisol and cortisol excretion in h ealthy subjects.2. The ratio of 6 beta-hydroxycortisol/cortisol was si gnificantly decreased (P = 0.036) in the 0-4 h fraction of urine after ingestion of grapefruit juice, but not in the 4-24 h fraction (P = 0. 218) or for the compiled data, fraction 0-24 h (P = 0.114). 3. These r esults indicate that endogenous cortisol metabolism may not only be of hepatic origin, but may also be dependent on the metabolic capacity o f cytochrome P450 IIIA (CYP3A) in the gut mucosa. 4. This finding may cast further doubts of the usefulness of the 6 beta-hydroxycortisol/co rtisol ratio as an indicator of hepatic CYP3A activity.