Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2004
Publication Date: October 20, 2004
Citation: Kim, J.G., Vallet, J.L. 2004. Secreted and placental membrane forms of folate-binding protein occur sequentially during pregnancy in swine. Biology of Reproduction. 71(4):1214-1219. Interpretive Summary: Folic acid (folate) is a vitamin that is required to make DNA and protein, which are essential for growth of the developing pig fetus. However, how folate is transported from the sow to the fetus during pregnancy is not fully understood. Previous results indicated that two folate binding proteins that potentially participate in this process are present within the uterus of the sow. One form is found free in solution in the contents of the uterus, the other is attached to cells. Production of these two proteins throughout pregnancy by various compartments of the uterus has not been investigated. In this experiment, production of the two types of folate binding protein was determined throughout pregnancy. Results indicated that the forms are produced sequentially, the soluble form is found within the uterus during early pregnancy. The cell-bound form is produced by the membranes that attach the fetus to the sow during later pregnancy. The sequential production of two different proteins to accomplish the transfer of a vitamin is a novel observation and suggests that the success of the transition between the two forms may have consequences for fetal survival and litter size in pigs.
Technical Abstract: The objective was to understand how two forms of folate binding protein interact to accomplish folate transport during pregnancy in swine. Specific folate binding was measured in uterine flushings during the estrous cycle and early pregnancy, and in allantoic fluid (secreted form), and placental membranes (membrane form) throughout later pregnancy. In addition, the localization of the secreted form of folate binding protein (sFBP) in uterine wall sections was assessed. Uterine flushings were collected on Days 10, 13, and 15 of the estrous cycle and pregnancy. Allantoic fluid and placentas were collected on Days 20, 35, 50, 70, 90, and 105 of pregnancy. Uterine wall sections were collected on all days of the experiment. Folate binding was measured by incubation of aliquots of uterine flushings, allantoic fluid or placental microsomal membranes with 0.5 to 4 nM [**3H]folate. Uterine wall sections were incubated with purified anti-FBP IgG or normal rabbit serum IgG to localize sFBP. Folate binding did not differ between early pregnancy and the estrous cycle in uterine flushings, was greatest from Day 50 to 70 of pregnancy in allantoic fluid, and was greatest from Day 50 of pregnancy onward in placental microsomal membranes. Staining for sFBP was present in the endometrial glands from Day 10 to 15 in cyclic gilts and from Day 10 to 20 in pregnant gilts. The pattern of folate binding and sFBP staining supports the concept that sFBP transports folate to the developing conceptus until placentation and then the placental form takes over folate transport.