Fig. 7.

Activation of platelets by thrombin leads to binding and activation of the protease-activated receptor-1 (PAR1) receptor on platelets. This causes platelet degranulation and release of factors such as ADP which potentiates the signal causing a strong aggregation response. Normally NO causes activation of soluble guanylyl cyclase (sGC), which prevents premature activation of platelets. However, in pulmonary hypertension (PH) the level of NO is reduced thus reducing the threshold of platelet activation.