Effect of Increased Urea Levels on Mouse Preimplantation Embryos Developed in Vivo and in Vitro

High plasma urea nitrogen concentration has been proposed as an important factor contributing to the decline in reproductive parameters of domestic animals. The aim of this study was to evaluate the effect of urea on the development of preimplantation embryos in a mouse model. During in vivo tests, acute renal failure (ARF) accompanied by hyper-uraemia was induced by intramuscular administration of glycerol (50%) into hind limbs of fertilised dams. During in vitro tests, embryos collected from healthy dams were cultured in a medium with the addition of various concentrations of urea from the 4-cell stage to the blastocyst stage. Stereomicroscopic evaluation and fluorescence staining of embryos obtained from dams with ARF showed that high blood urea is connected with an increase in the number blastocysts containing at least one apoptotic cell and in the incidences of dead cells per blastocyst, but it did not affect their ability to reach the blastocyst stage. In vitro tests showed that culture of embryos with urea at concentration of 10 mM negatively affected the quality of obtained blastocysts. Blastocysts showed significantly lower numbers of cells and increased incidence of dead cells. An increase in apoptosis incidence was observed even in blastocysts obtained from cultures with 5 mM urea. Urea at concentrations 50 mM and higher negatively affected the ability of embryos to reach the blastocyst stage and the highest used concentrations (from 500 mM) caused overall developmental arrest of embryos at the 4- or 5- cell stage. These results show that elevated levels of urea may cause changes in the microenvironment of developing preimplantation embryos, which can negatively affect their quality. Embryo growth remains un-affected up to very high concentrations of urea.