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, p ost partum corpora lutea, and of luteinised follicular cysts of cows were h arvested 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 popul ations of cyclic corpora lutea. These cells obviously differentiated into v ascular cells, connective tissue cells and small luteal cells. Proliferativ e activity was strongest in young corpora lutea and markedly reduced in the mature ones. During involution of corpora lutea of oestrous cycle Ki-67-po sitive cells were mainly found in vascular walls and connective tissue dist ricts. Luteinised follicular cysts closely resembled cyclic corpora lutes. Corpora lutea of pregnancy exhibited foci of immunopositive cells close to blood vessels and connective tissue septae during whole gestation. Post par tal luteal involution was characterised by Ki-67-positive cells within Vasc ular walls and the surrounding stroma. Results suggest that luteal cellular proliferation is restricted mainly to theca interna-derived cells, which m ay differentiate to stromal cells and parenchymal cells.