Effects of grapefruit juice on cortisol metabolism in healthy male Chinese subjects

Grapefruit juice (GFJ) inhibits intestinal CYP3A4 activity and it has been suggested that GFJ may also inhibit renal 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2), which converts cortisol to cortisone. This study examined the effect of GFJ on the urinary excretion of cortisol, cortisone and 6β-hydroxycortisol (6β-OHC) and their ratios to asses these effects. Healthy male Chinese subjects took single doses of GFJ (200, 400, and 600 mL, respectively) at weekly intervals. Urine was collected over 24 h the day before and following GFJ intake. Subsequently, volunteers drank 400 mL GFJ for 7 days and urine was collected from 0 to 4 h daily. GFJ had dose-dependent effects on increasing cortisol excretion (P <0.05) and the ratio of cortisol to cortisone (P <0.005) and reducing 6β-OHC excretion (P <0.05) and the ratio of 6β-OHC to cortisol (P <0.005). There was no significant effect on cortisone excretion. Maximal effects were observed within 4 h after GFJ ingestion. Repeated doses had persistent but no cumulative effects. GFJ significantly reduced the ratio of 6β-OHC to cortisol. It increased the ratio of cortisol to cortisone and this appeared largely due to increased cortisol excretion related to impaired CYP3A4-mediated cortisol metabolism although a true inhibitory effect on 11β-HSD2 in the kidney cannot be excluded.