Increased thromboxane biosynthesis in essential thrombocythemia.

In order to investigate the in vivo thromboxane (TX) biosynthesis in essential thrombocythemia (ET), we measured the urinary excretion of the major enzymatic metabolites of TXB2, 11-dehydro-TXB2 and 2,3-dinor-TXB2 in 40 ET patients as well as in 26 gender- and age-matched controls. Urinary 11-dehydro-TXB2 was significantly higher (p < 0.001) in thrombocythemic patients (4,063 +/- 3,408 pg/mg creatinine; mean +/- SD) than in controls (504 +/- 267 pg/mg creatinine), with 34 patients (85%) having 11-dehydro-TXB2 > 2 SD above the control mean. Patients with platelet number < 1,000 x 10 (9)/1 (n = 25) had significantly higher (p < 0.05) 11-dehydro-TXB2 excretion than patients with higher platelet count (4,765 +/- 3,870 pg/mg creatinine, n = 25, versus 2,279 +/- 1,874 pg/mg creatinine, n = 15). Average excretion values of patients aging > 55 was significantly higher than in the younger group (4,784 +/- 3,948 pg/mg creatinine, n = 24, versus 2,405 +/- 1,885 pg/mg creatinine, n = 16, p < 0.05). Low-dose aspirin (50 mg/d for 7 days) largely suppressed 11-dehydro-TXB2 excretion in 7 thrombocythemic patients, thus suggesting that platelets were the main source of enhanced TXA2 biosynthesis. The platelet count-corrected 11-dehydro-TXB2 excretion was positively correlated with age (r = 0.325, n = 40, p < 0.05) and inversely correlated with platelet count (r = -0.381, n = 40, p < 0.05). In addition 11 out of 13 (85%) patients having increased count-corrected 11-dehydro-TXB2 excretion, belonged to the subgroup with age > 55 and platelet count < 1,000 x 10(9)/1. We conclude that in essential thrombocythemia: 1) enhanced 11-dehydro-TXB2 excretion largely reflects platelet activation in vivo; 2) age as well as platelet count appear to influence the determinants of platelet activation in this setting, and can help in assessing the thrombotic risk and therapeutic strategy in individual patients.