[Ultrastructural changes during atresia in human ovarian follicles. I. Primordial follicles]

Ultrastructural signs of atresia were studied in healthy women between 25 and 36 years of age. As a morphologic correlate of incipient atresia the dispersion of the paranuclear complex of organelles (Balbiani's yolk nucleus) and a significant affection of mitochondria were detected. The latter structures showed higher electron density of the matrix and fewer cristae, compared with normal oocytes. Dilation of endoplasmic reticulum tubules and vesicles and presence of numerous various-sized ooplasmic vacuoles were noted. Deep invaginations and dilation of the nuclear envelope were also observed in terminal phases of atresia. The atretic follicles were lined by dark and light granulosa cells arranged partly over each other. The character of their cytologic changes was similar to those described in the oocytes. In most atretic follicles there were found deposits of extracellular material, after ruthenium red staining reminding of the zona pellucida, between the oocyte and the granulosa cells, sometimes exclusively between the granulosa cells.