Influence of Calcium and Magnesium Deprivation on Ovulation and Ovum Maturation in the Perfused Rabbit Ovary 1

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Abstract
The role of calcium (Ca2+) and magnesium (Mg2+) in the ovulation process was studied using in vitro perfused rabbit ovaries. Ovaries were perfused with or without human chorionic gonadotropin (hCG) in Ca2+/Mg2+-free medium (M199) alone or combined with standard M199 to yield varying concentrations of Ca2+ and/or Mg2+. In all ovaries perfused with hCG, ovulatory efficiency was similar regardless of the concentration of Ca2+ and/or Mg2+. In ovaries perfused in Ca2+/Mg2+-free medium without hCG, ovulatory efficiency was similar to that in ovaries perfused with hCG. As Ca2+/Mg2+ levels were increased without HcG, ovulatory efficiency declined. Ovulation time was significantly accelerated in ovaries perfused in Ca2+/Mg2+-free medium with or without hCG. Most ovulated ova from ovaries perfused without hCG were immature. With hCG, degree of ovum maturity was directly related to ovulation time. Ovarian smooth muscle contractions were undetectable in 3 ovaries perfused in Ca2+/Mg2+-free M199 despite occurrence of ovulation. Smooth muscle contractions were recorded in 2 of 3 ovaries perfused in standard M199 with hCG. Ca2+/Mg2+ exclusion results in rapid follicle rupture and immature ova. Oocyte maturation appears to be gonadotropin-dependent. Ovulation occurs in the absence of ovarian smooth muscle contractions during perfusion with Ca2+/Mg2+-free medium.