Trinucleate cells and the ultrastructural localisation of bovine placental lactogen.

Bovine placental lactogen activity is shown by immunogold electron microscopy to be restricted to the granules and the Golgi body from which they form in the bovine fetal trophectodermal binucleate cell, and granules of similar size and staining reaction in trinucleate "giant" cells found in the maternal uterine epithelium throughout pregnancy. These results support the hypothesis that a fetal binucleate cell forms a maternal giant cell by migration to and fusion with a uterine epithelial cell.