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Figure 1 Scheme of nitric oxide (NO) metabolism pathway. In this diagram the nitric oxide (NO) pathway is depicted. In presence of oxygen (O2) and/or alveolar ventilation, NO synthases (NOS) are activated and produce NO from L-arginine via L-citrulline. The NO activates soluble- and membrane-bound guanylate cyclases, which synthesize cyclic guanylate monophosphate (cGMP), which subsequently activates cGMP-kinase. This enzyme—by activation of K+-channels and subsequent Ca++-channel inhibition—evokes a reduction of intracellular Ca++ concentration, finally resulting in vasodilation. The downstream effects of NO are limited by phosphodiesterase (PDE)-induced degradation of cGMP.
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