Premature labor and failure of the cervix of soften, both manifestations of abnormal uterine function, are to major causes of fetal distress or mortality in human beings. The ovarian hormones estrogen, relaxin, and progesterone have been demonstrated to influence spontaneous contractile activity of the myometrium and extensibility of the uterine cervix in ovariectomized rats. However, the precise roles and interactions of these hormones on uterine function during pregnancy and parturition have not been elucidated. The aim of this project is to investigate the influence of estrogen, relaxin, and progesterone on both myometrial contractility and cervical extensibility during pregnancy and parturition in the rat. Initially, intact pregnant rats will be used for the characterization of myometrial activity throughout pregnancy parturition. This will be done using a small latex pressure recording ballon inserted into one uterine horn in a number of rats. Blood samples will be taken daily by means of jugular cannulae and assayed for estrogen, relaxin, and progesterone in order to enable correlation of myometrial activity and changes in cervical extensibility with serum hormone levels. The functions of estrogen, relaxin, and progesterone will be investigated by administering various combinations of these hormones to ovariectomized pregnant rats. The effects of these treatments on physiological events, i.e., myometrial activity, responsiveness of the myometrium to oxytocin near term, duration of parturition, fetal survival, and cervical extensibility will be investigated. A second approach which is less disruptive to the animals but more time-consuming will be employed to pursue the insights gained from the ovariectomized pregnant rat. Estrogen and relaxin will be selectively eliminated from the circulation by daily administration of specific antibodies to these hormones. The physiological events which will be monitored with this second approach are the same as those to be monitored with the ovariectomized pregnant rats. Information obtained from these studies should provide valuable insight into the causes and possible treatments for problems such as "premature uterine contractions" and the "unripe cervic" which frequently occur during human pregnancy.