title: Nitric oxide synthase activity in human seminal plasma.
abstract: OBJECTIVE
  To determine whether human seminal plasma possesses nitric oxide 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 have shown that nitric oxide can influence human sperm function in vitro.
  
  
  METHODS
  Semen samples were collected from 30 men presenting for an infertility evaluation at our institution. After a standard semen analysis, the semen samples were centrifuged at 10,000g, and the seminal plasma was collected and stored at -20 degrees C for later evaluation of the arginine concentration and calcium-dependent and calcium-independent NOS activity. NOS activity was measured by the conversion of [(3)H]L-arginine to [(3)H]L-citrulline.
  
  
  RESULTS
  NOS activity was detected in 28 of 30 seminal plasma samples tested. The mean +/- SD calcium-dependent NOS activity was 1.6 +/- 0.8 nmol/min/mL 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 seminal plasma was 7.0 +/- 1.9 mM. No significant correlations were found between the NOS activity in the seminal plasma and sperm concentration, sperm motility, or leukocyte concentration. The 2 men without detectable NOS activity in their semen had documented congenital bilateral absence of the vas deferens.
  
  
  CONCLUSIONS
  The results of this study demonstrate the presence of NOS activity 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 important source of NOS activity in semen.
authors.affiliation: James Buchanan Brady Foundation, Department of Urology, New York Presbyterian Hospital-Weill Medical College of Cornell University, New York, New York, USA.
authors.forename: A
authors.initials: A
authors.lastname: Zini
authors.forename: M K
authors.initials: MK
authors.lastname: O'Bryan
authors.forename: P N
authors.initials: PN
authors.lastname: Schlegel
mesh_terms: D000328:Adult; D001120:Arginine / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D009845:Oligospermia / Q000175:diagnosis / Q000378:metabolism; D012016:Reference Values; D012661:Semen / Q000201:enzymology*; D012680:Sensitivity and Specificity
chemical_list: D001120:Arginine; D019001:Nitric Oxide Synthase