NOS1 and diabetes mellitus: As shown in Fig. 6, diabetes significantly decreased cardiac BH4 concentrations, the ratio of nNOS dimers/monomers, phosphorylated nNOS (p-nNOS)/nNOS, eNOS dimers/monomers, and phosphorylated eNOS (p-eNOS)/eNOS and increased the expression of iNOS proteins in C57BL/6 WT mice compared with WT controls (P < 0.05 between WT STZ and WT controls, n = 4–5 hearts/group).