Developmental changes in sensitivity of bovine embryos to heat shock and use of antioxidants as thermoprotectants.

Experiments were conducted with in vitro-produced bovine embryos to determine whether 1) increased culture temperatures (i.e., heat shock) adversely affected embryonic development, 2) embryos become more resistant to heat shock as they advance in development, and 3) selective antioxidant molecules alleviate heat shock effects on embryonic development. Development of 2-cell embryos to > or = 16-cell stage on d 5 after in vitro fertilization was not affected by a heat shock of 40 degrees C for 3 h, but 41 or 42 degrees C for 3 h decreased (P = .004) development. In a separate experiment, development of 2-cell embryos was decreased (P = .01) by exposure to 41 degrees C for 3 h but not for 1 h. In contrast, development of morulae to blastocysts was not affected by heat shock of 41 degrees C for 1 or 3 h. Medium supplementation with 50 nM glutathione or 50 mM taurine before heat shock did not reduce the effects of heat shock (41 degrees C for 3 h) on 2-cell embryos. Likewise, addition of glutathione ester, a more membrane-permeable analog of glutathione, did not protect 2-cell embryos from heat shock. In conclusion, early bovine embryos are susceptible to disruption in development caused by heat shock. As embryos progress in development, they acquire resistance to heat shock. Glutathione, taurine, and glutathione ester were not effective in alleviating the effects of heat shock on development of 2-cell embryos. Consequently, molecules have yet to be identified that can protect early-stage bovine embryos from the adverse effects of heat shock.