Byssinosis: thromboxane release from human platelets by cotton dust and bract extracts

Extracts of cotton dust and bract induced in vitro release of arachidonic acid metabolite thromboxane A2 (TxA2), a potent bronchoconstricting agent, from human platelets. TxA2 release, determined by radioimmunoassay of the stabile metabolite TxB2, was both time- and dose-dependent. Cotton green bract extract was significantly more potent in releasing TxA2 from human platelets than cotton dust extract or cotton brown bract (field-dried bract) extract, while brown bract extract was least active, which suggests that the etiological agent(s) is of plant origin and not microbial in nature. TxA2 release was shown to be enzyme-dependent by inhibition of the reaction by indomethacin (cyclooxygenase inhibitor) and 7-(1-imidazolyl) heptanoic acid (thromboxane synthetase inhibitor). This study is the first to show in vitro platelet TxA2 release by cotton extracts and may provide an explanation for increased concentrations of TxB2, a metabolite of TxA2, in the bronchoalveolar spaces of rabbits exposed to aerosolized cotton dust extract. Platelet aggregation and production of TxA2 may prove to be an important mechanism in the pathogenesis of bronchoconstriction in byssinosis.