Methylene blue - an emerging vasopressor

Figure 1 Mechanism of methylene blue in selectively inhibiting inducible nitric oxide synthase that prevents nitric oxide generation. It does not block production of other isoform i.e. constitutive nitric oxide synthase which is required for various constitutive functions in the body. Further methylene blue also inhibits the activation of cyclic guanosine monophosphate by guanylate cyclase, ultimately all this prevents the extreme vasodilatation as shown in Figure 2. MB: Methylene blue; NO: Nitric oxide; iNOS: Inducible nitric oxide synthase; cGMP: Cyclic guanosine monophosphate.

Figure 2 Non selective inhibitor N(G)-methyl-L-arginine hydrochloride (molecule 546c88) inhibiting nitric oxide synthase and thus all downstream nitric oxide synthase isoforms resulting in complete blockade of production of nitric oxide causing increased mortality López et al[4]. NOS: Nitric oxide synthase; iNOS: Inducible nitric oxide synthase; cNOS: Constitutive nitric oxide synthase; eNOS: Endothelial nitric oxide synthase; nNOS: Neuronal nitric oxide synthase.