Attachment of the placenta to the uterus in pigs involves extracellular interaction between the expanding trophoblastic membrane and the thick glycocalyx present on the uterine epithelial microvilli. Formation of complexes between members of inter-alpha-trypsin inhibitor family may function in the maintenance of the extracellular matrix. This study investigated the change in the inter-alpha-trypsin inhibitor heavy chains (ITIH1, ITIH2, ITIH3 and ITIH4) during the oestrous cycle and early pregnancy in pigs. Gene expression of ITIH1, ITIH2, ITIH3 and ITIH4 was detected in the endometrium of cyclic and pregnant gilts; however, gene expression of ITIH was not altered throughout the oestrous cycle or early pregnancy. Western blot analysis with an ITIH antiserum identified the possible linkage forms of ITIH with the serine protease inhibitor, bikunin. Pregnancy altered the release of the various inter-alpha-inhibitor forms from the endometrium during the period of trophoblastic attachment. The results from this study indicate that the inter-alpha-trypsin inhibitor family plays an important role in maintenance of the uterine surface glycocalyx during placental attachment in pigs.
RD Geisert, MD Ashworth and Malayer JR
RD Geisert, CS Chamberlain, KA Vonnahme, Malayer JR and LJ Spicer
During early pregnancy, pig conceptuses initiate the synthesis of oestrogens and on day 12 their trophoblastic membranes undergo a rapid expansion throughout the uterine horns. The insulin-like growth factor (IGF) system may be involved with conceptus development and steroidogenesis in pigs. Changes in uterine luminal IGF, insulin-like growth factor binding proteins (IGFBPs) and enzymatic activity for cleavage of IGFBPs during the oestrous cycle and early pregnancy were investigated. Uterine luminal content of IGF-I and IGF-II in uterine flushings from pigs on day 12 of pregnancy were two and three times greater, respectively, compared with uterine flushings collected from gilts during the oestrous cycle. Both IGF-I and -II content decreased on day 15 of gestation but content of IGF-II in uterine flushings remained three times greater than that of cyclic gilts. IGFBP-2 and -3 were the predominant binding proteins present in uterine flushings during days 0-10 of the oestrous cycle or day 10 of pregnancy. No IGFBPs were detected in the uterine flushings of either cyclic or pregnant pigs after day 10 by ligand blotting. Incubation of [125I]-labelled IGFBPs with various protease inhibitors indicated that cleavage of [125I]-labelled IGFBP-2 and -3 in uterine flushings involved serine proteases such as tissue kallikrein and matrix metalloproteinases. The results of the present study indicate that an increase in tissue kallikrein activity on day 12 of the oestrous cycle and pregnancy in pigs can directly, or indirectly through activation of matrix metalloproteinases, cleave IGFBP-2 and -3, thus allowing uterine release of IGF-I and -II in the uterine lumen to stimulate conceptus development.