Proposed Mechanisms Controlling Parturition and the Induction of Parturition in Swine

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Abstract
The initiation and completion of parturition in swine is dependent on the termination of progesterone production and the initiation of active processes bringing about expansion of the birth canal and the uterine contractions causing delivery. Evidence is presented to support the hypothesis that the fetuses initiate the sequence of events leading to delivery. Present evidence indicates that the sequence of events leading to parturition start with pituitary stimulation of Cortisol production by the adrenal glands, followed by Cortisol causing stimulation of the production or release of prostaglandin F2α, probably by the uterus. Prostaglandin F2α was shown to cause luteolysis and release of relaxin from the corpora lutea as well as the release of oxytocin from the pituitary gland. It also caused stimulation of uterine contractions sufficient to bring about delivery. Parturition and lactation were both induced to occur prematurely by either prostaglandin F2α or the glucocorticoid, dexamethasone, and the results of field trials suggest that prostaglandin F2α or one of its analogs could be used to cause parturition to occur on a specified day. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.