Sex and age-related differences in the urinary excretion of TXB2 in normal human subjects: a possible pathophysiological role of TXA2 in the aged kidney.

Urinary excretion of thromboxane B2 (TXB2), a stable metabolite of TXA2, was measured by radioimmunoassay in 58 normal subjects (17 males and 41 females) aged from 19 to 98 years. The basal level of urinary TXB2 in normal subjects was 100 +/- 6.7 ng/day (mean +/- SEM). In young males, contamination of urine specimens with seminal fluid, which is known to contain large amounts of prostaglandin E, did not change the level of urinary TXB2. Urinary excretion of TXB2 was significantly higher in male subjects than in female (124 +/- 12.6 vs 90 +/- 7.4 ng/day, p less than 0.05). There was no significant age-related difference in 24-h urinary excretion of TXB2 in normal subjects. However, when urinary excretion of TXB2 was expressed as a function of urinary creatinine excretion, it was significantly higher in the elderly (60-93 years old) than in the younger subjects (19-59 years old)(141 +/- 15.7 vs 99 +/- 7.7 ng/g creatinine, p less than 0.02). Renal TXA2 may have a pathophysiological role in the functional impairment of the kidney in elderly people.