The long-term objective of this proposal, as in the previous project period, is to study placental angiogenesis (development of the placental blood supply), and its role in supporting utero-placental and fetal growth. The mammalian placenta is the organ through which nutrients, gases and wastes are exchanged between the maternal and fetal systems. Thus, size of the placental blood supply has a profound influence on the rate of transplacental exchange, and thereby on the rate of fetal growth. Factors affecting fetal development, in turn, have a significant influence on postnatal survival and growth. The specific goals of the proposed research are to isolate and characterize angiogenic factor(s) produced by maternal and fetal placental tissues. Based upon preliminary evidence indicating that endometrial tissues of ewes secrete heparin-binding angiogenic factor(s), immunoblotting and immunohistochemical techniques also will be used to evaluate expression of heparin-binding growth factors by placental tissues. To accomplish these goals, placental tissues will be obtained from ewes throughout early gestation (preattachment through definitive implantation stages; Exp. 1) and mid-late gestation (periods of maximal and then decreasing rates of placental growth; Exp. 2). An additional study (Exp. 3) is designed to examine in vivo effects of heparin-binding angiogenic factors on uterine angiogenesis. Ewes will be utilized in the proposed experiments because ontogeny of placental production of angiogenic factor(s) was well characterized during the previous grant period, and, in addition, placental vascular function has been well studied in this species. Additionally, ruminant placentas are comprised of highly vascular structures (placentomes) consisting of maternal caruncles and fetal cotyledons, as well as interplacentomal areas consisting of intercaruncular endometrium and intercotyledonary chorioallantois. This placental arrangement provides a unique opportunity to study differences not only between maternal and fetal portions but also between functionally specialized portions of the placenta. Knowledge of factors which influence placental vascular development should lead to a better understanding of how fetal and maternal placental tissues interact to support fetal growth. In addition, because placental vascular development is one of the few instances of angiogenesis in a non-pathological situation, isolation and characterization of angiogenic factors produced by placental tissues will be important not only for gaining a better understanding of placental function but also for understanding regulation of angiogenic processes in general.
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