Differences in the urinary excretion of 6-beta-hydroxycortisol/cortisol between Asian and Caucasian women

The urinary ratio of 6-beta-hydroxycortisol/cortisol has been used as a non invasive probe for human cytochrome P450 3A4 isoforms (CYP3A4). Ethnic-rela ted differences in the ratio have not been evaluated. The aim of this study was to determine if there are differences in the ratio between Asian and C aucasian women over a menstrual cycle. First-morning urine samples were col lected every other day starting from the second day of menstruation far a c omplete menstrual cycle From 25 Asians and 26 Caucasian women who were 18 t o 40 years old, healthy nonsmoking, and alcohol and drug free, including or al contraceptives. Urine concentrations of 6-beta-hydroxycortisol and corti sol were measured by high-pressure liquid chromatography (HPLC). For statis tical analysis, three phases of the menstrual cycle were evaluated menstrua tion (days 1-4), follicular or postmenstruation (days 6-10), and the luteal phase (days 21-24) based on the average menstrual cycle (28 days). Statist ical analysis was performed by an independent sample t-test using the Bonfe rroni correction far repeated measures. Large intersubject and intrasubject variations of the 6-beta-hydroxycortisol/cortisol ratios were absented dur ing the menstrual cycles in bath ethnic groups. Asian women had a statistic ally significant lower ratio than Caucasian women did for all three phases of the menstrual cycle: 2.2 +/- 1.1 versus 5.1 +/- 3.5, 2.1 +/- 1.1 versus 6.0 +/- 4.9, and 2.8 +/- 1.6 versus 5.6 +/- 3.0 for the menstruation, folli cular, and luteal phases, respectively. The two- to threefold lower 6-beta- hydroxycortisol/cortisol ratios in Asian women suggest that Asian women may have a lower CYP3A activity compared with Caucasian women. Differences in ethnicity may mask potential gender-related effects if ethnic background is not evaluated as a contributing factor. (C) 1999 the American College of C linical Pharmacology.