Administration of Cinaciguat decreased BP and increased HR in both apo-sGC mice and WT mice. In fact, the BP-lowering effect of Cinaciguat in apo-sGC mice is significantly greater and longer lasting than in WT mice. In addition, Cinaciguat decreased BP in apo-sGC mice at concentrations that did not affect BP in WT mice. Furthermore, the IC₅₀ values for Cinaciguat-induced ex vivorelaxation of precontracted aortas are threefold lower in apo-sGC mice than in WT mice (IC₅₀=0.2 nM and 0.7 nM, respectively). Together, our results suggest that sGC activators like Cinaciguat but not sGC stimulators like BAY 41-2272 activate apo-sGC. In addition, the observation that Cinaciguat can modulate vasorelaxation and BP in WT mice suggests that even in healthy mice, a subset of the available sGC pool is haem-free and responsive to sGC activators^[2].