Nitric Oxide or N.O for short is something that is a by-product of testosterone that allows a man to achieve and maintain an erection.
Men that are testosterone deficient lack N.O and often therefore have erection difficulties.
Viagra increases N.O, this is the reason it has the results it does.
N.O or its lack is not a factor in the aetiology (cause) of gynecomastia.
However it you lack N.O the symptom for which would most likely be erection difficulties, then it is possible that you may (not neccessarily though) have this problem due to a lack of testosterone and a lack of testosterone is a major cause of gynecomastia.
Low testosterone or hypogonadism as it is known is an associated condition to gynecomastia, with 10% of all gynecomastia sufferers having hypogonadism.
All men with gynecomastia and particularly those contemplating surgery should have pathology investigations with an endocrinologist that has an interest in reproductive endocrinology.
These doctors are specialists in the causes of gynecomastia unlike plastic surgeons that are only experts in gynecomastia removal.
I can help people obtain details of said endocrinologists should the need arise.