Although cAMP-PDE activity is globally increased in PASMCs from PAH patients, the PDE4 activity does not contribute to this, because PDE4 activity decreases in PAH patients (30% of total) compared to controls (around 45%); meanwhile, there was an increase in activities ascribed to PDE1 and PDE3 [52]. Here, PDE4A is linked to pulmonary arterial hypertension.