Erectile dysfunction and NO: variations of NO penile blood levels before and after sildenafil treatment

Erectile dysfunctions are not uncommon, especially in patients suffering from metabolic syndrome and from a number of circulatory and psychiatric problems. cGMP diesterase inhibitors, such as sildenafil, have proven to be beneficial in the treatment of many such conditions. Our patients, all of them complaining of erectile dysfunction, were treated with sildenafil (50 mg, thrice a week for 6 weeks). All patients reported beneficial effects and were not clinically distinguishable (interview and Doppler scores). We sampled blood for systemic circulation (cubital vein) and from penis (corpora cavernosa) before and after prolonged sildenafil treatment, and measured nitrate (+nitrite) levels in plasma and in red blood cells (RBCs). Hemoglobin is a powerful catalyst of NO oxidation to nitrate, and we thought that nitrate in RBC might be a more sensitive parameter than plasma nitrate. We found that the ratio of penile vs systemic blood plasma nitrate was similar in all patients before or after sildenafil treatment. On the other hand, the same parameter measured in RBC showed that, at the beginning of treatment, patients could be divided into two groups: one with a high ratio and the other with a low ratio. Therefore, clinically similar patients could be biochemically divided into two populations. The difference disappeared after treatment, thus hinting at a curative effect of the drug. The mechanisms underlying this behavior are still unknown and the clinical implication of two populations that can be distinguished by RBC nitrate is yet to be evaluated.