title: Beneficial Effects of Nitric Oxide Induced Mild Oxidative Stress on Post-Thawed Bull Semen Quality.
abstract: BACKGROUND
  Cryopreservation of semen requires optimized conditions to minimize the harmful effects of various stresses. The main approach for protection of sperm against stress is based on the use of antioxidants and cryoprotectants, which are described as defensive methods. Recently, the application of controlled mild stressors has been de- scribed for activation of a temporary response in oocyte, embryo and somatic cells. In this study a sub-lethal oxidative stress induced by precise concentrations of nitric oxide (NO) has been evaluated for sperm during cryopreservation.
  
  
  METHODS
  In this experimental study, we used different concentrations of NO [0 µM (NO-0), 0.01 µM (NO-0.01), 0.1 µM (NO-0.1), 1 µM (NO-1), 10 µM (NO-10) and 100 µM (NO-100)] during cryopreservation of bull semen. Their effects on post-thawed sperm quality that included motility and velocity parameters, plasma mem- brane functionality, acrosome integrity, apoptosis status, mitochondrial activity and lipid peroxidation after freezing-thawing were investigated.
  
  
  RESULTS
  Exposure of sperm before freezing to NO-1 significantly increased total motility (88.4 ± 2.8%), progressive motility (50.4 ± 3.2%) and average path velocity (VAP, 53.8 ± 3.1 µm/s) compared to other extenders. In addition, NO-1 significantly increased plasma mem- brane functionality (89.3 ± 2.9%) compared to NO-0 (75.3 ± 2.9%), NO-0.01 (78.3 ± 2.9%), NO-0.1 (76.4 ± 2.9%), NO-10 (64 ± 2.9%) and NO-100 (42 ± 2.9%). Sperm exposed to NO-1 produced the highest percentage of viable (85.6 ± 2.3%) and the lowest percentage of apoptotic (10.8 ± 2.4%) spermatozoa compared to the other extenders. Also, NO-100 resulted in a higher percentage of dead spermatozoa (27.1 ± 2.7%) compared to the other extenders. In terms of mitochondrial activity, there was no significant difference among NO-0 (53.4 ± 3.2), NO-0.01 (52.1 ± 3.2), NO-0.1 (50.8 ± 3.2) and NO-1 (53.1 ± 3.2). For acrosome integrity, no significant different was observed in sperm exposed to different concentrations of NO.
  
  
  CONCLUSIONS
  Induction of sub-lethal oxidative stress with 1 µM NO would be beneficial for cryopreservation of bull semen.
authors.affiliation: Department of Animal Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Sharafi
authors.affiliation: Department of Animal Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Zhandi
authors.affiliation: Department of Embryology at Reproduction Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACER, Tehran, Iran.
authors.forename: Abdolhossein
authors.initials: A
authors.lastname: Shahverdi
authors.affiliation: Department of Animal Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
authors.forename: Malak
authors.initials: M
authors.lastname: Shakeri
keywords: Bull; Cryopreservation; Nitric Oxide; Oxidative Stress; Sperm