Ultrastructural changes in the endometrium of rabbit induced by spermatozoa

Experiments were undertaken to investigate whether ultrastructural changes could be visualized in the endometrial epithelial linings brought about by the presence of spermatozoa. Female rabbits were inseminated with intact spermatozoa in one uterine horn, and the other horn was injected with inactive (dead) spermatozoa, which served as the control. Ruthenium red was used to enhance contrast of glycoproteins of epithelial plasma membranes. There was a decrease in the number and height of microvilli of epithelial cells in those horns injected with intact spermatozoa along with a decrease of ruthenium red deposits. In contrast, microvilli were numerous in those horns injected with inactive spermatozoa, and ruthenium red deposits also were numerous. This marker was not seen between neighboring epithelial cells in any of the injected horns. Control virgin animals, however, disclosed ruthenium red deposits in luminal plasma membranes and along the junctional complexes of epithelial cells. Intact spermatozoa could modify the synthesis or turnover of glycoproteins of outer coats owing to a possible cell-to-cell interaction between spermatozoa and endometrium. The lack of ruthenium red deposits in junctional complexes in the injected animals and their presence in the virgin control rabbits suggest the opening of communicating channels in the two former groups due possibly to the PMSG priming not present in the virgin control animals.