title: Response of midpiece vesicles on human sperm to osmotic stress.
abstract: BACKGROUND
  We investigated the osmotic response of midpiece vesicles (MPV) on human sperm.
  
  
  METHODS
  Light microscopy, transmission X-ray microscopy and computer-aided semen analysis was used to investigate sperm in normozoospermic semen from healthy donors, separated from semen and suspended in hyper- or hypo-osmotic solutions.
  
  
  RESULTS
  The mean incidence of MPV-bearing sperm in semen was 31% (range 8-71; n = 47). MPV were morphologically different from cytoplasmic droplets. The incidence of MPV-bearing sperm in separated populations increased reversibly after washing in Sperm Preparation Medium but not after washing in seminal plasma. There was an inverse relationship between medium osmolality and both MPV-bearing sperm incidence and MPV diameter. However, initial osmolality in semen from different donors did not correlate with incidence of MPV-bearing sperm. Furthermore, a direct relationship was observed in semen as osmolality increased with time. No correlation existed between progressive motility and semen osmolality. Progressive motility and the amplitude of lateral head displacement were significantly reduced in sperm with an MPV (three out of four semen samples, 26-32 sperm). The incidence of MPV-bearing sperm in those that had penetrated cervical mucus (75, 46, and 40%) was increased compared with the adjacent semen (24, 35, and 24%).
  
  
  CONCLUSIONS
  MPV are ubiquitous and distinct from cytoplasmic droplets. They respond to osmolality changes of the surrounding medium. The presence of an MPV can reduce motility but not survival in cervical mucus. Therefore, they should not be considered detrimental to sperm function.
authors.affiliation: ISA, Institute for Storage Ring Facilities, University of Aarhus, 8000 Aarhus C, Denmark. jabraham@ifa.au.dk
authors.forename: Joanna V
authors.initials: JV
authors.lastname: Abraham-Peskir
authors.forename: Eric
authors.initials: E
authors.lastname: Chantler
authors.forename: Erik
authors.initials: E
authors.lastname: Uggerhøj
authors.forename: Jens
authors.initials: J
authors.lastname: Fedder
mesh_terms: D002582:Cervix Mucus / Q000502:physiology; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D011859:Radiography; D012016:Reference Values; D012661:Semen / Q000502:physiology; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure*; D013312:Stress, Physiological / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology*; D013997:Time Factors