“An increase in the release of the vasoconstrictor thromboxane A₂, suggesting the activation of platelets, occurs in both the primary and secondary forms of pulmonary hypertension.” By contrast, the release of prostacyclin is depressed in these patients.   Whether the imbalance in the release of these mediators is a cause or a result of pulmonary hypertension is unknown, but it may play a part in the development and maintenance of both forms of the disorder."