Consequences of Nitric Oxide Synthase Inhibition During Bovine Oocyte Maturation on Meiosis and Embryo Development

The importance of nitric oxide synthase (NOS) in bovine oocyte maturation was investigated. Oocytes were in vitro matured with the NOS inhibitor Nw- l-nitro-arginine methyl-ester (10⁻⁷, 10⁻⁵ and 10⁻³ m l-NAME) and metaphase II (MII) rates and embryo development and quality were assessed. The effect of l-NAME (10⁻⁷ m) during pre-maturation and/or maturation on embryo development and quality was also assessed. l-NAME decreased MII rates (78-82%, p < 0.05) when compared with controls without l-NAME (96%). Cleavage (77-88%, p > 0.05), Day 7 blastocyst rates (34-42%, p > 0.05) and total cell numbers in blastocysts were similar for all groups (146-171 cells, p > 0.05). Day 8 blastocyst TUNEL positive cells (3-4 cells) increased with l-NAME treatment (p < 0.05). For oocytes cultured with l-NAME during pre-maturation and/or maturation, Day 8 blastocyst development (26-34%) and Day 9 hatching rates (15-22%) were similar (p > 0.05) to controls pre-matured and matured without NOS inhibition (33 and 18%, respectively), while total cell numbers (Day 9 hatched blastocysts) increased (264-324 cells, p < 0.05) when compared with the controls (191 cells). TUNEL positive cells increased when NOS was inhibited only during the maturation period (8 cells, p < 0.05) when compared with the other groups (3-4 cells). NO may be involved in meiosis progression to MII and its deficiency during maturation increases apoptosis in embryos produced in vitro. Nitric oxide synthase inhibition during pre-maturation and/or maturation affects embryo quality.