Postovulatory aging of human ova: I. Light microscopic observations

Abstract

AbstractThe morphologic changes undergone by the human secondary oocyte following ovulation were assessed by light microscopy in 57 specimens recovered from the Fallopian tube and endometrial cavity between 24 and 144 hr after the luteinizing hormone peak in plasma. Ovarecovered shortly after ovulation were surrounded by a large cumulus mass comprising approximately 20,000 follicular cells. Whenever it was possible to perform a detailed observation of the perivitelline space in these ova, the presence of a polar body was recognized. The oocyte usually occupied an excentric position within the cumulus. Ovum denudation appeared to proceed by breakdown of the cumulus into fragments and release of the oocyte with a small number of cells attached to the zona. As a consequence of this process the oocyte surrounded by a few layers of cells frequently coexisted with large fragments of the cumulus. Progress of ovum denudation was time dependent and proceeded at a relatively slow pace. Some uterine ova still had cells attached to the zona. At 96 hr after the LH peak 40% of the ova underwent fragmentation of the cytoplasm giving rise to anucleated pieces of varying sizes. The dimensions of the zona pellucida and ooplasm presented wide individual variations as well as some time related changes. The mean external diameter of the zona ± SD of 43 ova was 161.6 ± 14.6 μm.The occurrence of denudation and cytoplasmic fragmentation were more clearly related to the postovulatory age of the ovum than to the site of recovery. The rate of denudation of human oocytes seems to proceed at a much lower speed in comparison with small mammals currently used as laboratory animals.