title: Tolerance of spermatozoa to hypotonic stress: role of membrane fluidity and correlation with cryosurvival.
abstract: The aim of this study was to evaluate inter-individual variability in osmotic properties of stallion spermatozoa and its correlation with cryosurvival. In addition, temperature dependency of hypo-osmotic tolerance and membrane fluidity were studied. Stallion sperm membranes exhibited good resistance towards hypotonic stress in the 15-30 °C temperature range, whereas membrane stability was found to be decreased at 4 and 37 °C. Bull spermatozoa showed greater hypo-osmotic tolerance compared with stallion spermatozoa, especially at temperatures above 30 °C, which coincided with decreased membrane fluidity of bovine spermatozoa in this temperature range. The critical osmolality at 22 °C, at which half of the sperm population survived exposure to hypotonic saline solution, was found to vary between 55 and 170 mOsm kg(-1) among different stallions. Clear correlations were found for pre- versus post-freeze sperm motility and membrane integrity. Pre-freeze percentages of membrane-intact spermatozoa after exposure to hypotonic stress showed a weak correlation with sperm motility after cryopreservation. This correlation, however, was not found when data were corrected for initial numbers of membrane-intact spermatozoa in the sample. We thus conclude that studies on pre-freeze tolerance towards hypotonic stress cannot be used to predict sperm cryosurvival rates for individual stallions.
authors.affiliation: Clinic for Horses - Unit for Reproductive Medicine, University of Veterinary Medicine Hannover, Bünteweg 15, D-30559 Hannover, Germany.
authors.forename: Harriëtte
authors.initials: H
authors.lastname: Oldenhof
authors.affiliation: Clinic for Horses - Unit for Reproductive Medicine, University of Veterinary Medicine Hannover, Bünteweg 15, D-30559 Hannover, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Heutelbeck
authors.affiliation: Clinic for Cattle, University of Veterinary Medicine Hannover, Bischofsholer Damm 15, D-30173 Hannover, Germany.
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Blässe
authors.affiliation: Clinic for Cattle, University of Veterinary Medicine Hannover, Bischofsholer Damm 15, D-30173 Hannover, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Bollwein
authors.affiliation: National Stud Lower Saxony, Spörckenstraße 10, D-29221 Celle, Germany.
authors.forename: Gunilla
authors.initials: G
authors.lastname: Martinsson
authors.affiliation: Institute of Multiphase Processes, Leibniz Universität Hannover, Callinstrasse 36, D-30167 Hannover, Germany.
authors.forename: Willem F
authors.initials: WF
authors.lastname: Wolkers
authors.affiliation: Clinic for Horses - Unit for Reproductive Medicine, University of Veterinary Medicine Hannover, Bünteweg 15, D-30559 Hannover, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Sieme
mesh_terms: D000818:Animals; D001947:Breeding / Q000379:methods; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology*; D015925:Cryopreservation / Q000379:methods*; D005434:Flow Cytometry; D005858:Germany; D006736:Horses / Q000502:physiology*; D008297:Male; D009997:Osmotic Pressure / Q000502:physiology*; D013045:Species Specificity; D017550:Spectroscopy, Fourier Transform Infrared; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology*; D013696:Temperature