Ultrastructure of mullerian and wolffian ducts of fetal rabbit in vivo and in organ culture.

Emphasis is put on programmed cell death in the epithelial cells of mullerian and wolffian ducts, in rabbit fetuses, by observations on the timing and ultrastructural characteristics of cell degeneration. Genital tracts were collected on days 17 to 25 post-coitum and processed for electron microscopy. An organ culture assay was performed on fetal ducts and testis or ovary, for 4 days. Then, ducts and gonads were processed for electron microscopy. The involution of male mullerian and female wolffian ducts in culture and in vivo follows a similar pattern. Cell degeneration is initialized by an increase in the number of lysosomes which are subsequently involved in invading autophagic vacuoles. Cytochemical localizations of acid phosphatase and aminopeptidase indicate the presence of new lysosomes within the cells. In conclusion, this cell degeneration seems to be due to a double lysosome system in the rabbit urogenital ridge: A mullerian one spontaneously inactive when mullerian inhibiting substance is absent, and a wolffian one, spontaneously active when testosterone is absent. The organ culture is reliable for further attempts to study the responses to substances known to act on lysosome formation or activity.