ABSTRACT
Although we have a basic understanding of the biochemical and morphological changes that occur during mammalian preimplantation embryo development, from oocyte fertilization by spermatozoa to the zygote or 1-cell embryo, through early cleavage stages, compaction of the morula, and culminating in the formation of the blastocyst, large gaps in our knowledge remain. A great deal of literature has been published about nitric oxide (NO) (evidenced by over 76 000 papers produced by a Medline search), but much less is understood about its role in embryo development (only 94 papers). The current literature regarding its role in preimplantation embryo development has not been reviewed for several years.1 This chapter therefore reviews the role of NO as a regulator of cell cycle progression in embryo development from the 1-cell to the blastocyst stage, based upon literature published from 19982 through to the most recent advances in 2006.3
NO is a gaseous free radical molecule that has been shown to be an intracellular messenger. NO is produced in a variety of tissue types and plays many important roles, including smooth muscle relaxation, vasodilation, neuronal signaling, and stimulation of the immune response, as well as regulating preimplantation embryo development.4-6 It has also been shown to regulate other reproductive processes including steroidogenesis, folliculogenesis, tissue remodeling, and angiogenesis, cervical ripening, and uterine contractility during pregnancy.7
