the three pathways described above are all targeted by currently available medical therapies for pah. however, several other pathways have been identified that are also altered in pah and are being investigated as potential targets for future therapies. for example, the mitochondrial enzyme pyruvate dehydrogenase kinase (pdk) is pathologically activated in pah, causing a metabolic shift from oxidative phosphorylation to glycolysis and leading to increased cell proliferation and impaired apoptosis. expression of vasoactive intestinal peptide, a potent vasodilator with anti-inflammatory and immune-modulatory roles, is reduced in pah, while expression of its receptor is increased.