Determination of nitric oxide metabolites by means of the Griess assay andgas chromatography-mass spectrometry in the cavernous and systemic blood of healthy males and patients with erectile dysfunction during different functional conditions of the penis

Recent research implicated that the relaxation of cavernous arterial and tr abecular smooth muscle - the crucial event in penile erection - is initiate d by the release of nitric oxide (NO) from nerve terminals within the caver nous tissue as well as from the endothelia that line the lacunar spaces and the intima of penile arteries. The present study was undertaken to determi ne whether plasma levels of the NO metabolites nitrate (NO3-) and nitrite ( NO2-) in the systemic and cavernous blood of male subjects change during di fferent penile conditions, and whether there is a difference in the NO3- an d NO2- levels of normal males and patients with erectile dysfunction (ED). Twenty-four potent adult male volunteers and 15 patients with ED were expos ed to visual and tactile erotic stimuli in order to elicit penile tumescenc e and, in the group of healthy volunteers, rigidity. Whole blood was aspira ted from the corpus cavernosum and the cubital vein, and NO3- and NO2- leve ls were determined in plasma aliquots by means of the Griess reaction and a method combining gas chromatography and mass spectrometry (GC-MS). The mea n systemic and cavernous plasma NO3-/NO2- level in blood samples obtained f rom the healthy volunteers was 25-31 muM when determined by means of the Gr iess reaction and 37-41 muM when measured by GC-MS. Both approaches reveale d that NO3-/NO2- levels in the peripheral and cavernous blood do not change appreciably during developing erection, rigidity and detumescence. Moreove r, no significant differences were found between NO3-/ NO2- plasma levels i n the systemic and cavernous blood samples taken from the normal subjects a nd patients during penile flaccidity, tumescence and detumescence. Our resu lts may reflect the fact that NO metabolism in the corpora cavernosa in the phases of penile tumescence and rigidity may account for only a minor frac tion of local levels of NO3- and NO2-, which may also derive from exogenous sources. Moreover, the basal levels of NO metabolites in the blood flushin g the lacunar spaces of the cavernous body in the state of developing erect ion could conceal any release of NO that may occur within the penile tissue . Thus, we conclude that the quantification of NO metabolites by means of a dvanced detection methods, such as GC-MS, is of no use in the workup of ED.