Uniqueness of Drug: Riociguat is the only treatment approved in the U.S. for use in two types of PH. It stimulates soluble guanylate cyclase (sGC), an enzyme in the cardio-pulmonary system and the receptor for nitric oxide (NO). NO binds to sGC and catalyzes synthesis of cyclic guanosine monophosphate (cGMP), which in turn activates protein kinase G regulation of cytosolic calcium ion concentration. This cascade changes actin-myosin contractility, resulting in vasodilation. In healthy individuals, NO acts as a signaling molecule on vascular smooth muscle cells to induce vasodilation. NO binds to sGC and mediates the synthesis of the secondary messenger cGMP. sGC forms heterodimers consisting of a larger alpha-subunit and a smaller heme-binding beta-suburiit. The synthesized cGMP acts as a secondary messenger and activates cGMP-dependent protein kinase (protein kinase G) to regulate cytosolic calcium ion concentration.
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