STUDY OF CHANGES IN UTERINE MAST-CELLS DURING EARLY-PREGNANCY IN THE RAT

The number of mast cells in the uterus of the pregnant rat was studied at times ranging from Night 3 of gregnancy (vaginal sperm or plugs found on Day 1) to Night 5 when blastocyst attachment had occurred in all animals. The mast cells were stained using toluidine blue and counted in the myometrium and endometrium. The number of mast cells observed increased from the pre-attachment phase of pregnancy (Night 3 or Day 4) to reach a maximum on Day or Night 5 and then fell during Day/Night 5, during the development of blastocyst attachment. The possible involvement of mast cells in ovum implantation is discussed.