title: Expression of enkephalin-degrading enzymes in human semen and implications for sperm motility.
abstract: OBJECTIVE
  To investigate the presence of two enkephalin-degrading enzymes (aminopeptidase N [APN] and neutral endopeptidase 24.11 [NEP]) in different fractions of human semen, their distribution in sperm cells, and their effect on sperm motility.
  
  
  METHODS
  We performed expression assays for APN and NEP by real-time polymerase chain reaction, Western blot, and immunofluorescence techniques in sperm cells and performed motility analysis after incubation of semen samples with enzyme inhibitors and the opioid receptor antagonist naloxone.
  
  
  METHODS
  Assisted reproduction unit and academic research laboratory.
  
  
  METHODS
  Semen from 50 normozoospermic healthy human donors.
  
  
  METHODS
  Spermatozoa isolated from semen on a discontinuous Percoll gradient (40%-80%), followed by swim-up, were used for all techniques except for sperm motility analysis, for which fresh semen was used.
  
  
  METHODS
  Immunoblotting blots, indirect immunofluorescence antibody assays, cycle threshold values for real-time polymerase chain reaction, and percentage of motile sperm.
  
  
  RESULTS
  We found APN in the equatorial segment of the upper post-acrosomal region of the sperm head, in the neck and along the tail of spermatozoa, in prostasomes, and in seminal fluid, whereas NEP was present in a very restricted area of a few sperm cells and in prostasomes. Messenger RNA of both enzymes was detected in spermatozoa. The inhibition of enkephalin-degrading enzymes attenuated the time-dependent decrease of sperm motility; this effect was reversed by naloxone.
  
  
  CONCLUSIONS
  Enkephalin-degrading enzymes are present in human semen and may be involved in the control of sperm motility, mainly by the regulation of endogenous opioid peptides.
authors.affiliation: Department of Physiology, Faculty of Medicine and Dentistry, University of the Basque Country, Leioa, Spain. nerea.subiran@ehu.es
authors.forename: Nerea
authors.initials: N
authors.lastname: Subirán
authors.forename: Ekaitz
authors.initials: E
authors.lastname: Agirregoitia
authors.forename: Asier
authors.initials: A
authors.lastname: Valdivia
authors.forename: Carmen
authors.initials: C
authors.lastname: Ochoa
authors.forename: Luis
authors.initials: L
authors.lastname: Casis
authors.forename: Jon
authors.initials: J
authors.lastname: Irazusta
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000626:Aminopeptidases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018826:CD13 Antigens / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D015260:Neprilysin / Q000235:genetics / Q000378:metabolism; D018847:Opioid Peptides / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012661:Semen / Q000378:metabolism*; D013081:Sperm Motility / Q000187:drug effects / Q000502:physiology*; D015244:Thiorphan / Q000494:pharmacology; D014018:Tissue Distribution
chemical_list: D000596:Amino Acids; D007093:Imidazoles; D018847:Opioid Peptides; D011480:Protease Inhibitors; D012333:RNA, Messenger; C069912:leuhistin; D015244:Thiorphan; D000626:Aminopeptidases; C025579:enkephalin degrading enzyme; D018826:CD13 Antigens; D015260:Neprilysin