Development of bovine IVF oocytes cultured in medium supplemented with a nitric oxide scavenger or inhibitor in a co-culture system

Bovine IVF oocytes were cultured in modified bovine embryo culture medium ( mBECM) supplemented with either a nitric oxide (NO) scavenger, hemoglobin ( Hb, 1 mu g/mL) and/or a NO synthesis inhibitor, L omega-nitro-L-arginine me thyl ester (L-NAME, 1 or 1000 nM) in a cumulus-granulosa cell co-culture sy stem. In Experiment 1, a total of 1,675 cumulus-oocytes complexes was colle cted for 7 mo and cultured to the blastocyst stage in mBECM with or without Hb after IVM and IVF. There were significant (P<0.0024) model effects of H b addition and month of oocyte collection on embryo development. A signific ant (P<0.0023) monthly variation was detected in all developmental stages. However, addition of Hb to mBECM consistently enhanced embryo development t o the blastocyst stage over all months. No statistical differences were fou nd in the interaction between Hb addition and month except for the cleavage rate. Overall, a greater percentage of oocytes developed to the 8-cell (P< 0.0459), 16-cell (P<0.001), morula (P<0.0013) and blastocyst (P<0.0024) sta ges after the addition of Hb. In Experiment 2, addition oft-NAME to mBECM s upplemented with Hb did not further stimulate prehatched development. In co nclusion, the promoting effect of Hb on in vitro development of embryos is highly repeatable over an extended period of time. (C) 1999 by Elsevier Sci ence Inc.