GUCY2C and pulmonary arterial hypertension: These include the PDE5 inhibitor, sildenafil, approved for the treatment of erectile dysfunction and pulmonary hypertension (53), and the synthetic GUCY2C ligands, plecanatide and linaclotide, which target the secretory function of GUCY2C to treat chronic idiopathic constipation and constipation-predominant irritable bowel syndrome (28).