A histochemical study of succinate dehydrogenase in mouse oocytes and early embryos

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Abstract
A positive succinate dehydrogenase [SDH] reaction was seen in [mouse] oocytes and embryos of all stages examined. There was no reaction in the absence of succinate. Succinate dehydrogenase concentration progressively increased during follicular growth, reaching a maximum in preovulatory oocytes; no further change was detected in the tubal unfertilized egg. There were no large variations in SDH activity during early cleavage, but an increase occurred at the blastocyst stage. The volume of the dictyate oocyte increases about 7-fold during the growth period examined; therefore the increase in enzyme activity/oocyte appears to be even greater. This may be due to an increase in the absolute number of mitochondria per oocyte and/or to an increase enzyme activity per mitochondrion. The increase of SDH activity which characterizes the blastocyst stage accords with the structural changes (formation of well developed transverse cristae) observed in the mitochondria at this stage and with the increased metabolic activity of the embryo at this time. The apparent lack of variation in enzymatic activity in the embryo before the blastocyst stage, however, does not exclude the possibility that minor changes may occur, since variations in SDH activity of less than 35% cannot be detected with certainty by histochemical methods.
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