Effect of Ca2+/Mg2+-free Culture Condition on Spontaneous First Cleavage of Rat Oocytes.

Abstract

The aim of this study was to investigate the effect of Ca2+- and Mg2+-free culture conditions on induction of spontaneous first cleavage in rat oocytes. Oocytes recovered from superovulated Wistar females 17 h after hCG injection were exposed for 1.5 h to Ca2+/Mg2+-free, Ca2+-free, Mg2+-free, or control mKRB medium supplemented with 5 μg/ml cytochalasin-B (CB). The oocytes were then cultured for 4.5 h in control medium containing CB and for 28 h in CB-free control medium. The oocytes exposed to the Ca2+/Mg2+-free medium (23%) cleaved better than those exposed to Ca2+-free (8%), Mg2+-free (0%), or control (0%) media. The cleavage rates of oocytes recovered 12, 17 and 22 h after hCG injection and exposed to the Ca2+/Mg2+-free medium were 4, 17 and 22%, respectively. The efficiency of oocyte activation in 1.25 mM Sr2+ treatment for 6 h was not influenced by the culture background of bivalent cations (cleavage rates: both 49% in Ca2+/Mg2+-free and Ca2+-free medium). These results indicate that Ca2+/Mg2+-free culture condition induced the spontaneous first cleavage of rat oocytes in an age dependent manner, but had no additional effect on Sr2+-induced oocyte activation.