Effect of oxygen concentration and free radicals on in vitro development of in vitro-produced bovine embryos.

The effects of free radicals and hypotaurine on the development of bovine embryos produced by in vitro fertilization of in vitro-matured oocytes were examined. Embryos that developed to the 4- to 6-cell stage after in vitro fertilization were cultured without feeder cells in TCM199 medium supplemented with 1% calf serum (CS) under either 5% CO2 in air or 5% O2, 5% CO2 and 90% N2. The percentages of blastocysts (including early, expanding, and hatched stages) that developed under 5% O2 was higher (P < .01) than the percentage of those that developed under 20% O2. The respective percentages in 5% vs 20% O2 concentration were as follows: blastocysts (d 8), 49% vs 17%; expanded blastocysts (d 8), 19% vs 6%; hatched blastocysts (d 10), 16% vs 0%. The development of embryos to blastocysts was suppressed (P < .05) when oxygen radicals were generated in culture medium by 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) under both 5% and 20% O2. The addition of hypotaurine permitted the development of embryos to blastocyst stage in medium with AAPH only under 5% O2 (P < .05), but superoxide dismutase (SOD) did not permit the development of embryos to blastocysts. Alternatively, when embryos were cultured in medium without AAPH, the rates of development into blastocysts under 20% O2 increased (P < .05) by the addition of hypotaurine and SOD. However, under 5% O2, the rates of blastocyst formation were not improved by addition of hypotaurine and SOD. Moreover, the cell numbers of blastocysts cultured in medium containing hypotaurine were greater (P < .01) than those of blastocysts cultured in medium without hypotaurine. It is concluded that hypotaurine may exert beneficial effects on in vitro development of bovine embryos under both 20% O2 and 5% O2 of gaseous conditions.