Calcium plays an essential role in regulating many cellular functions, including proliferation, differentiation, and apoptosis. In spite of its importance in the establishment and maintenance of pregnancy, changes in
calcium levels at the maternal-conceptus interface during pregnancy and its action on endometrial gene expression are not well understood. Thus, we examined changes in
calcium levels in the endometrium during pregnancy,
calcium deposition at the maternal-conceptus interface during pregnancy, and the role of
calcium on the expression of endometrial genes related to conceptus implantation during early pregnancy in pigs. The amounts of endometrial
calcium increased during mid- to late pregnancy, and
calcium deposition was mainly localized to endometrial and chorionic epithelial cells at the maternal-conceptus interface during pregnancy and conceptus tissues during early pregnancy. The amounts of total recoverable
calcium in uterine
flushings were greater on Day 12 of pregnancy than Day 12 of the estrous cycle, and
estrogen increased absorption of
calcium ions by endometrial tissues. Increasing endometrial
calcium levels by treatment with
A23187, a
calcium ionophore, decreased the expression of the
estrogen-responsive endometrial genes AKR1B1, ESR1, FGF7, IL1RAP, LPAR3, S100G, SPP1, and STC1 and increased the expression of genes related to
prostaglandin synthesis and transport, namely PTGES,
PTGS2, and SLCO5A1. These data suggest that
calcium ions at the maternal-conceptus interface play a critical role in the establishment and maintenance of pregnancy in pigs by regulating the expression of endometrial genes involved in conceptus implantation, as well as the attachment of endometrial epithelial and conceptus trophectoderm/chorionic epithelial cells during pregnancy.