Urine immunoreactive thromboxane B2 in rat cardiac allograft rejection.

Increases in urinary excretion of immunoreactive thromboxane B2 (i-TXB2), the stable break-down product of thromboxane A2, have been described in kidney allograft rejection in patients. We investigated these findings by monitoring daily urine i-TXB2 excretion in a heterotopic cardiac allograft rat model using Lewis rats as recipients. In order to obtain differences in allograft survival, a donor was used that was either ACI or LewisxBrown Norway F1 (LxB-NF1). The ACI-to-Lewis model rejected on day 6.2 +/- 0.2 (n = 6). The LxB-NF1-to-Lewis model received, in addition, azathioprine (5 mg/kg/daily) and rejected on day 9.1 +/- 0.8 (n = 9). Urinary i-TXB2 excretion increased significantly in both groups, compared with i-TXB2 values measured following sham surgery or isograft transplantation. Thus increases in urinary i-TXB2 appear to be associated with cardiac allograft rejection.