Thromboxane A2, as an unstable intermediate between the prostaglandin endoperoxides and thromboxane B2, is a potent inducer of platelet aggregation and causes vasoconstriction.
15(R)-Pinane thromboxane A2 is the (R)-epimer of pinane thromboxane A2 . 15(R)-PTA2 does not inhibit collagen-induced platelet aggregation (IC50s = 120-130 μM). It does not affect gastric tone in isolated rat gastric fundus when used at concentrations of 0.5 or 1.5 μg ml and is less effective than PTA2 at inhibiting prostaglandin-induced contraction of isolated rat stomach muscle.
Thromboxane B2 (TXB2) is released in substantial quantities from aggregating platelets and metabolized during circulation to 11-dehydro TXB2 and 2,3-dinor TXB2. In rats and rabbits, 2,3-dinor TXB1 has been identified as another urinary metabolite of TXB2. However in human urine, only trace amounts of 2,3-dinor TXB1 have been identified. In rats, 2,3-dinor TXB1 is excreted at a much higher rate than 2,3-dinor TXB2 (19.2 ± 4.9 ng/24 hr and 1.6 ± 0.3 ng/24 hr, respectively). Therefore, urinary 2,3-dinor TXB1 is a suitable marker of thromboxane biosynthesis in rats.
Thromboxane B3 (TXB3), the stable hydrolysis product of TXA3, is synthesized from eicosapentaenoic acid (EPA) through the action of COX and thromboxane synthase enzymes. This compound is biosynthesized in several tissues, including seminal vesicles, lungs, polymorphonuclear leukocytes (PMNL), and ocular tissues.
Thromboxane B2 (TXB2) is a compound significantly released from aggregating platelets and undergoes metabolic transformation during circulation into 11-dehydro TXB2 and 2,3-dinor TXB2. The latter, 2,3-dinor TXB2, serves as a prevalent urinary metabolite of TXB2 and acts as an indicator for in vivo TXA2 synthesis. Studies have shown that in healthy male volunteers, the median excretion rate of 2,3-dinor TXB2 is measured at 10.3 ng hour, equivalent to 138 pg mg of creatinine.
11-Dehydro-2,3-dinor Thromboxane B2 (11-dehydro-2,3-dinor TXB2) is a metabolite derived from the inactive TXA2 metabolite, TXB2. Its formation involves the action of cytosolic aldehyde dehydrogenase (ALDH) and β-oxidation processes. Remarkably, levels of 11-dehydro-2,3-dinor TXB2 have been observed to increase by 5.2-fold in a surgery-induced rat model of tendon overuse, highlighting its potential role in physiological stress responses.