title: Impaired ovulation in mice with targeted deletion of the neuronal isoform of nitric oxide synthase.
abstract: BACKGROUND
  Nitric oxide (NO) plays an important role in numerous reproductive processes. To date, most studies have assessed the role of NO by using nonspecific pharmacological inhibitors of the precursor to NO, nitric oxide synthase (NOS). These pharmacological NOS inhibitors suppress all isoforms of NOS; thus, the precise contribution of each isoform to female reproductive physiology is unknown. The purpose of this study was to determine the specific role of neuronal NOS (nNOS) in the regulation of ovulation in female mice lacking the gene that encodes for nNOS (nNOS-/-).
  
  
  METHODS
  Ovulation was assessed in wild-type (WT) and nNOS-/- female mice by examining the number of ovarian rupture sites and number of oocytes recovered from the oviducts following mating or exposure to exogenous gonadotropins (i.e., 5 IU pregnant mares serum gonadotropin [PMSG] and 5 IU human chorionic gonadotropin [hCG]). Ovulatory efficiency was determined as the number of ovulated oocytes per number of ovarian rupture sites. To examine whether ovulatory deficits in nNOS-/- mice were due to alternations in central mechanisms, plasma luteinizing hormone (LH) concentrations were assessed in WT and nNOS-/- mice that were challenged with 25 ng of gonadotropin-releasing hormone (GnRH). To determine whether ovulatory deficits in nNOS-/- mice were due to local ovulation processes, nerves innervating the reproductive tract of WT and nNOS-/- females were examined for the presence of nNOS protein.
  
  
  RESULTS
  There were substantial fertility deficits in nNOS-/- female mice; the nNOS-/- mice had fewer oocytes in their oviducts following spontaneous and gonadotropin-stimulated ovulation. Pituitary responsiveness to exogenous GnRH challenge was intact in nNOS-/- mice. Dense nNOS protein staining was observed in nerves innervating the reproductive tracts of WT mice.
  
  
  CONCLUSIONS
  The reproductive deficits in nNOS-/- females are most likely due to alternations in the transfer of oocytes from the ovaries to the oviducts during ovulation. These results suggest that defects in neuronally derived NO production may contribute to female infertility.
authors.affiliation: Department of Psychology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Klein
authors.forename: D
authors.initials: D
authors.lastname: Carnovale
authors.forename: A L
authors.initials: AL
authors.lastname: Burnett
authors.forename: E E
authors.initials: EE
authors.lastname: Wallach
authors.forename: H A
authors.initials: HA
authors.lastname: Zacur
authors.forename: J K
authors.initials: JK
authors.lastname: Crone
authors.forename: V L
authors.initials: VL
authors.lastname: Dawson
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelson
authors.forename: T M
authors.initials: TM
authors.lastname: Dawson
mesh_terms: D000818:Animals; D005260:Female; D018390:Gene Targeting; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009412:Nerve Fibers / Q000201:enzymology; D009474:Neurons / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I; D010060:Ovulation / Q000502:physiology*; D011247:Pregnancy
chemical_list: D007527:Isoenzymes; D007986:Luteinizing Hormone; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse