Triglyceride content of bovine oocytes and early embryos

Abstract

A microfluorescence technique was used to measure the triglyceride content of a minimum of two bovine oocytes or preimplantation embryos up to the hatched blastocyst stage. Embryos were produced in vitro from abattoir-derived ovaries and grown in medium containing synthetic oviductal fluid, amino acids and BSA (SOFaaBSA medium); 10% fetal calf serum was added to some of the embryos at the four-cell stage. Before maturation, the triglyceride content of oocytes was 59 +/- 1.37 ng and it decreased (P < 0.05) after maturation to 46 +/- 0.85 ng. A decrease in triglyceride content (P < 0.05) was also observed after fertilization with the formation of the two-cell embryo (34 +/- 1.80 ng). In the absence of serum, the triglyceride content remained relatively constant from the two-cell to the hatched blastocyst stage. The triglyceride content of blastocysts produced in vivo was similar (33 +/- 0.70 ng) to that of blastocysts produced in vitro in the absence of serum. In contrast, the triglyceride content of embryos grown with 10% fetal calf serum increased steadily from the 9-16-cell stage to a value in hatched blastocysts (62 +/- 1.14 ng) almost double that in serum-free conditions. These results indicate that triglyceride may act as energy source during bovine oocyte maturation and fertilization and that the presence of serum causes excessive synthesis or accumulation of triglyceride in early embryos.

Does serum cause lipid-droplet accumulation in bovine embryos produced in vitro, during developmental days 1 to 4?

“…Lipid accumulation was found and quantified from day 4 of development until the blastocyst stage of embryos cultured with serum [21]. Further, in the blastocyst stage of bovine embryos, the relative abundance of mRNA for lipidogenics genes increased regarding the previous stages [4].…”

“…Neither did Crosier et al [15], with the same kind of serum and a similar technique used by us to quantify, studying the morula stage. However, on day 4 of embryos cultured with serum since day 2 (9-16 cells), Ferguson and Leese [21], observed that the triglyceride content increases in regard to the previous days and to the same stage without serum. Although the technique used by us to quantify lipids might not have been sensitive enough to detect the accumulation such as the one used by Ferguson and Leese [21], it is possible that 10 % v/v of fetal serum used by them generate earlier accumulation than the 5 % v/v estrous serum used by us and Crosier et al [15].…”

“…In embryos cultured in serum-free medium, according to Ferguson and Leese [21], triglycerides the main content of lipid droplets, remain constant between 2-cell stage and blastocysts. In our study, lipids increase at day 4 due to a couple of embryos (Fig.…”

“…Also, glucose is one of the most important components of serum, and even more important in fetal than in adult serum [45]. It is possible that this difference would lead to Ferguson and Leese [21] to find early lipids accumulation in embryos of 4 days of development.…”

The effect of nutrition and metabolic status on the development of follicles, oocytes and embryos in ruminants

“…Fatty acids are an endogenous source of energy during oocyte maturation; several lines of evidence support the idea of fatty-acid oxidation as a source of essential ATP for oocyte maturation and for early development of the embryo. For example, the triglyceride content of the bovine oocytes decreased during in vitro maturation (IVM), as well as after fertilization (Ferguson and Leese, 1999). In addition, lipase activity was increased in the bovine oocytes following IVM (Cetica et al, 2002).…”