Postfertilization manipulation of mammalian embryos results in various developmental alterations. To determine whether the manipulation of the Ca²⁺ regime causing oocyte activation is a valuable experimental means in helping understand the biological process by which embryos integrate signals from outside and later regulate gene expression, we linked Ca²⁺ signal parameters i.e. amplitude, number and frequency, with the efficiency and quality of postimplantation development. Freshly ovulated rabbit oocytes were subjected to repetitive and modulated Ca²⁺ influx. The results provide three major pieces of information. Firstly, the Ca²⁺ stimulus is the most efficient signal activating mammalian eggs when it is applied in a repetitive manner, the amplitude being the crucial factor.

Secondly, the dynamics of early cleavage does not appear to be determined by either the frequency or the amplitude of modulation of the Ca²⁺ signal that activates the oocyte. Thirdly, amplitude and temporal modulation of the Ca²⁺ signal in the early minutes influences the developmental performance and the morphology of the rabbit parthenogenetic conceptus at day 11.5 of pregnancy. The results demonstrate the importance of epigenetic events during postfertilization as well as the possible uses of Ca²⁺ modulation in studying long term developmental effects.