Nitric oxide synthase activity in human seminal plasma

Objectives. To determine whether human seminal plasma possesses nitric oxid e synthase (NOS) activity and whether, if present, this activity correlates with standard semen analysis parameters. Recent studies have demonstrated the presence of NOS in the epithelium of the male reproductive tract and ha ve shown that nitric oxide can influence human sperm function in vitro. Methods, Semen samples were collected from 30 men presenting for an inferti lity evaluation at our institution. After a standard semen analysis, the se men samples were centrifuged at 10,000g, and the seminal plasma was collect ed and stored at -20 degreesC for later evaluation of the arginine concentr ation and calcium-dependent and calcium-independent NOS activity. NOS activ ity was measured by the conversion of [H-3]L-arginine to [H-3]L-citrulline. Results, NOS activity was detected in 28 of 30 seminal plasma samples teste d. The mean +/- SD calcium-dependent NOS activity was 1.6 +/-0.8 nmol/min/m l and the mean calcium-independent NOS activity was 1.0 +/-0.7 nmol/min/ml of the seminal plasma. The mean +/- SD arginine concentration in the semina l plasma was 7.0 +/-1.9 mM. No significant correlations were found between the NOS activity in the seminal plasma and sperm concentration, sperm motil ity, or leukocyte concentration. The 2 men without detectable NOS activity in their semen had documented congenital bilateral absence of the vas defer ens. Conclusions, The results of this study demonstrate the presence of NOS acti vity in human semen and support a role of nitric oxide in sperm function in vivo. Our results also suggest that the seminal vesicles may be an importa nt source of NOS activity in semen. UROLOGY 58: 85-89, 2001. (C) 2001, Else vier Science Inc.