Rapid recovery of in vivo prostacyclin formation after inhibition by aspirin. Evidence from measurements of the major urinary metabolite of prostacyclin by GC-MS.

The effect of aspirin on the in vivo formation of prostacyclin and thromboxane A2 in normal healthy individuals was studied by measuring the urinary excretion of 2,3-dinor-6-keto-PGF1 alpha and 2,3-dinor-TxB2 by gas chromatography-mass spectrometry. Administration of 500 mg aspirin twice daily caused a sustained reduction in the excretion of 2,3-dinor-TxB2 to 10-15% of the predose value, while the excretion of 2,3-dinor-6-keto-PGF1 alpha was reduced for only about 3 hours after the aspirin dose. The data demonstrate a considerable difference in the inhibitory effect of aspirin on the in vivo synthesis of thromboxane A2 and prostacyclin.