Production of in vitro bovine embryos supplemented with l-carnitine in different oxygen tensions and the relation to nitric oxide

The aim of this study was to evaluate the production of bovine embryosin vitrowhen supplemented withl-carnitine for 24 h beginning on day 5 (d 5) under two different oxygen tensions (20% or 5%) and the relationship of nitric oxide (NO) inin vitroculture (IVC) medium to embryo development. Cumulus-oocyte complexes (COC;n= 837) were maturedin vitrofor 24 h and fertilization was performed for 18 h. Zygotes were culturedin vitrofor 9 days afterin vitrofertilization in synthetic oviductal fluid (SOF) medium with 5% fetal calf serum. At d 5 the plates were assigned to one of four treatment groups: high (20%) or low (5%) O(2)tension either with or without the addition of 3.03 mMl-carnitine (High-Cont, High-Lcar, Low-Cont, Low-Lcar). The concentration of NO in the culture medium was evaluated on d 5, d 6 and d 9. On d 7, parts of the embryos were submitted for evaluation of intracellular lipid droplets. The cleavage rate was similar (P> 0.05) between high and low O(2)tension and the blastocyst rate was similar in all conditions evaluated. The hatching rate was higher (P <0.05) for Low-Cont. The NO concentration was higher at d 9 under low O(2)tension (P <0.1). The addition of 3.03 mMl-carnitine between d 5 and d 6 of IVC was not efficient in reducing cytoplasmic lipid content of bovine embryos. Additionally, IVC at a low oxygen tension withoutl-carnitine promoted better conditions for embryo development. A higher concentration of NO in medium was observed under low O(2)tension.