Histochemical Demonstration of Lipids in Cultured Porcine Oocytes and Preimplantation Embryos

Changes in the number of lipid droplets during meiotic maturation, fert i l ization and early development were histochemically examined in cultured porcine oocytes and embryos. The oocytes and embryos possessed Sudanophilic lipids composed of small (<2.5 μm), medium (2.5–4.9 μm) and large (≥5.0 μm) droplets. In oocytes soon after collection, the numbers of Sudanophilic lipid droplets with small and medium sizes were few and the number of those with large size was 148 ± 11.36. After being cultured for 22 and 44 hrs, the number of lipid droplets with large size remarkably decreased, while the number of those with small and medium sizes increased. The numbers of lipid droplets of each size in the oocytes 4 and 8 hrs after insemination were similar to those in oocytes 44 hrs after maturation culture. On the other hand, the number of lipid droplets in embryos did not vary greatly between the pronuclear and the 16-cell stages, but gradually decreased a f te r the moru la s tage . Expanded blastocysts had few small and medium lipid droplets and 11 ± 1.68 large ones. The present findings confirmed that lipid droplets contained in oocytes become smaller in size and larger in number. Since the smaller lipid droplets appear not to be used in the process of fertilization, we presume that they are mainly used as an energy source for the formation and expansion of blastocysts.