Fig. 5. Changes in cyclic guanidine monophosphate (cGMP) levels in SNPiP treatment compared to the levels in SNAP treatment. cGMP level of SNPiP-treated cells gradually increases without attaining a distinctive peak during the observation period, in contrast to the cGMP level in SNAP- and S-nitroso-N-benzoyl-D-penicillamine (SNBP)-treated cells, where the peak levels are rapidly attained.