Submitted to: Neuroendocrinology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/1999
Publication Date: N/A
Interpretive Summary: The birth process, parturition, is critical in the development of an individual which demands that many events in the dam and the offspring occur in the proper magnitude and at the proper time. Prior to birth, there is an increase in relaxin secretion. Relaxin is the hormone responsible for relaxation of the cervix and opening of the birth canal. Physiological regulation and consequences of this increase in relaxin secretion at the end of pregnancy is not fully understood. The present study sought to gain insight into the relationships among changes in relaxin concentrations and the other hormonal changes occurring at the end of pregnancy. Removal of the source of relaxin at the end of pregnancy resulted in a substantial transient increase in the circulating levels of prolactin. The decline in relaxin following the preparturient increase may synchronize the secretion of oxytocin which stimulate the uterine contractions required for birth, and prolactin which is essential in milk production. Full understanding and control of these processes may improve the success of the pregnancy.
Technical Abstract: In gilts, circulating concentrations of relaxin reach an antepartum peak within 2 days of parturition. During this time, many endocrine changes are occurring in preparation for birth. The present study was performed to determine the effect in pregnant gilts of intravenously administered relaxin on the circulating concentrations of oxytocin and prolactin. Six mid- gestational and eight late-gestational gilts were utilized in this study. Gilts from each gestational period were assigned to one of two treatment groups: relaxin or isotonic saline. Gilts received one of the two treatments and were subsequently bled at sequential time points for a 3 h duration. Prior to treatment, late-gestational gilts were ovariectomized to remove the primary source of endogenous relaxin (followed by progesterone administration to maintain pregnancy). It was concluded that acute exposure to relaxin had no significant effect on the circulating levels of either prolactin or oxytocin at the late- gestational ages. In the mid-gestational group, however, removal of endogenous relaxin did unexpectedly result in a substantial transient increase in the circulating levels of oxytocin and a lesser, yet significant increase in the circulating levels of prolactin.