S-Nitrosylation of endothelial nitric oxide synthase alters erectile function

Erectile dysfunction (ED) is a sentinel symptom in men with cardiovascular disease. Endothelial dysfunction and decreased bioavailability of nitric oxide (NO) is a common link between ED and related co-morbidities. Neuronal and endothelial nitric oxide synthases (nNOS and eNOS) play major roles in generating NO bioactivity necessary for erectile function. S-nitrosylation can inhibit eNOS activity. Thus, the presence of S-nitrosylated NOS in the penis and the potential impact of NOS S-nitrosylation/denitrosylation on erectile function were examined. S-nitrosylated forms of NOS were identified by biotin switch/Western blot. The erectile response in C57BL6 and S-nitrosoglutathione reductase null (GSNOR^−/−) mice were assessed by continuous cavernous nerve electrical stimulation (CCNES). Injection of glutathione ethyl ester was used to pharmacologically manipulate S-nitrosylated NOS levels. Immunohistological and immunofluorescence analyses identified the location of eNOS and GSNOR in corporal tissue. eNOS and nNOS were S-nitrosylated in unstimulated penises of wild type mice. CCNES resulted in a time-dependent increase in eNOS S-nitrosylation with peak eNOS S-nitrosylation observed during detumescence. S-nitrosylated nNOS levels were unchanged. eNOS and GSNO-R co-localize to the endothelium of the corpus cavernosum. S-Nitrosylated eNOS levels were elevated in the penis of GSNOR^−/− mice compared to C57BL6 animals. Intracorporal pressure measurements obtained during CCNES demonstrate GSNOR^+/− and GSNOR^−/− animals cannot maintain tumescence. Results suggest that eNOS S-nitrosylation/denitrosylation is an important mechanism regulating eNOS activity during erectile function and GSNO-R is a key enzyme involved in the denitrosylation of eNOS. The increase in eNOS S-Nitrosylation (inactivation) observed with tumescence may begin a cycle leading to detumescence.