Abstract
Thromboxane A2 (TXA2) is produced from arachidonic acid by cyclooxygenase-1 (COX-1) in thrombocytes and for the most part is converted to 11-dehydro-thromboxane B2 (11d-TXB2), the final stable metabolite.
Daily excretion amounts of 11d-TXB2 in urine are well correlated with the extent of inhibition of COX-1 by aspirin. Since the collection of 24-hour urine that is generally used for such evaluation is a lot of work, we studied the validity of using spot urine for this purpose. The intra-day variation in urinary 11d-TXB2 levels was studied in six healthy volunteers. Urinary concentrations of 11d-TXB2 were measured using a commercial enzyme immunoassay kit. The urinary excretion rate of 11d-TXB2 was expressed as the concentration ratio of 11d-TXB2 vs. creatinine. The results showed that there was no marked variation in intra-day urinary excretion rates, the range being within of that for urine collected over 24 hours for each volunteer. However, the urinary excretion rate of 11d-TXB2 was slightly decreased at around 7 pm for almost all of the volunteers. These results indicated that spot urine could be used in place of 24-hours urine collection for evaluating 11d-TXB2 levels.
