Figure 3: Relationship between endothelial cells and nitric oxide (NO) synthesis, as implicated in HFpEF pathophysiology. Pathways shown represent experimental evidence to date; avenues for future experimental investigation are highlighted by ‘?’. Abbreviations: NO, nitric oxide; eNOS, NOS, nitric oxide synthase, eNOS, endothelial derived nitric oxide synthase; nNOS, neuronal nitric oxide synthase; BH4, tetrahydrobiopterin (NOS cofactor); O˙2ˉ, superoxide; HTN, hypertension. Landmesser et al. [63], Silberman et al. [64].