Cellular proliferation in bovine luteal tissues of different reproductive states as demonstrated by Ki-67 immunocytochemistry.

Luteal tissue specimens of corpora lutea of oestrous cycle and pregnancy, post partum corpora lutea, and of luteinised follicular cysts of cows were harvested at slaughter. Cellular proliferation was examined employing Ki-67 immunocytochemistry. Ki-67 immunoreactivities could mainly be demonstrated within the nuclei of the theca interna and theca externa derived cell populations of cyclic corpora lutea. These cells obviously differentiated into vascular cells, connective tissue cells and small luteal cells. Proliferative activity was strongest in young corpora lutea and markedly reduced in the mature ones. During involution of corpora lutea of oestrous cycle Ki-67-positive cells were mainly found in vascular walls and connective tissue districts. Luteinised follicular cysts closely resembled cyclic corpora lutea. Corpora lutea of pregnancy exhibited foci of immunopositive cells close to blood vessels and connective tissue septae during whole gestation. Post partal luteal involution was characterised by Ki-67-positive cells within vascular walls and the surrounding stroma. Results suggest that luteal cellular proliferation is restricted mainly to theca interna-derived cells, which may differentiate to stromal cells and parenchymal cells.