title: Autocrine regulation of human sperm motility by the met-enkephalin opioid peptide.
abstract: OBJECTIVE
  To verify the presence of protein precursor pro-enkephalin (PENK) and met-enkephalin in human spermatozoa and to characterize the effects of exogenous and endogenous enkephalins on sperm motility.
  
  
  METHODS
  We carried out expression assays for met-enkephalin and its protein precursor PENK by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunofluorescence techniques in sperm cells and motility analysis after incubation of semen samples with met-enkephlin enzyme inhibitors and the opioid receptor antagonist naloxone. Met-enkephalin secretion was analyzed by flow cytometry.
  
  
  METHODS
  Assisted reproduction unit and academic research laboratory.
  
  
  METHODS
  Semen from 50 normozoospermic healthy human donors.
  
  
  METHODS
  Spermatozoa isolated from semen on discontinuous Percoll gradient (40%-80%) followed by a swim-up was used for all techniques.
  
  
  METHODS
  Immunoblotting blots, indirect immunofluorescence antibody assays, RT-PCR blots, flow cytometry plots, and percentage of motile sperm.
  
  
  RESULTS
  We found by RT-PCR and immunofluorescence that met-enkephalin and its protein precursor PENK are present in the head of human sperm cells. Endogenous met-enkephalin increased sperm motility, whereas the addition of exogenous met-enkephalin had a biphasic effect on motility, likely due to the activation of distinct receptor subtypes.
  
  
  CONCLUSIONS
  We provide evidence for a new role of met-enkephalin as an endogenous mediator of sperm motility. This autocrine regulation of sperm function by the opioid system represents a new mechanism of regulation of male factor fertility and could be useful as an emerging target for male contraception.
authors: Department of Physiology, Faculty of Medicine and Dentistry, University of the Basque Country, Leioa, Bizkaia. nerea.subiran@ehu
authors: Nerea
authors: N
authors: Subirán
authors: Luz
authors: L
authors: Candenas
authors: Francisco M
authors: FM
authors: Pinto
authors: Antonio
authors: A
authors: Cejudo-Roman
authors: Ekaitz
authors: E
authors: Agirregoitia
authors: Jon
authors: J
authors: Irazusta
mesh_terms: D000293:Adolescent; D000328:Adult; D004744:Enkephalin, Methionine / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D004745:Enkephalins / Q000032:analysis / Q000502:physiology; D005455:Fluorescent Antibody Technique; D006801:Humans; D008297:Male; D011498:Protein Precursors / Q000032:analysis / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013081:Sperm Motility / Q000187:drug effects
chemical_list: D004745:Enkephalins; D011498:Protein Precursors; C029992:proenkephalin; D004744:Enkephalin, Methionine