PDE4A and pulmonary arterial hypertension: Support for the therapeutic potential of combined treatment with a prostacyclin analogue and cAMP-PDE inhibitor comes from studies on monocrotaline- [43] and hypoxia-induced rat models of pulmonary hypertension [15], the anti-proliferative effects of iloprost in vivo being potentiated by the inhibition of PDE4 and/or PDE3 hydrolytic activity.