Observations on Rat Oocyte Maturation in Vitro: Morphology and Energy Requirements

Denuded ovarian oocytes, obtained from prepuberal rats, were incubated under oil and their development was studied by time-lapse cinemicrography. Polar bodies were formed about 8 h after autopsy and showed active movements immediately following abstriction. The oocyte membrane did not show contraction wrinkles during polar body formation as had been observed in mouse oocytes. Unfertilized tubal oocytes formed a second polar body in vitro about 45 min after isolation. Rat ovarian oocytes were able to utilize pyruvate, lactate, and possibly even an endogenous energy source for maturation. The absence of oxygen prevented maturation. It is suggested that oxygen (oxidation-reduction potential changes) may trigger oocyte maturation in Vivo. The formation of the second polar body in vitro is not inhibited by KCN, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, or the absence of oxygen, which indicates that the initiation of the second maturation division, unlike that of the first meiotic division, does not require generation of ATP by oxidative metabolism. Tubal oocytes lose the capacity to form a second polar body in the evening on the day of estrus.

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