A sizable problem in our understanding of the control of parturition has been a desire by different investigators to explain the whole mechanism in terms of their current theory. We have been offered explanations in terms of factors such as withdrawal of the systemic progesterone block, the local progesterone block, the volume:progesterone ratio, the progesterone:estrogen ratio, the oxytocin effect, the progesterone:oxytocin effect, the fetal role, and the prostaglandin role. With the coming of age of Endocrinology and the ability to reduce hormone assays to a routine laboratory service, we have at last begun to understand that many, if not all, rather than any one of these individual explanations may be implicated in the control of parturition. We now recognize that in late pregnancy a train of events is initiated that ultimately results in the delivery of the fetus. However, we still do not know exactly how and where that train starts, or exactly how it exerts its ultimate action on the myometrial cell. It is a major objective of this chapter to try to bring together some of the abovementioned theories, and particularly to show that, for example, the role of the fetus in the initiation of parturition and the concept of progesterone withdrawal may be part of the same mechanism. It would be folly to say that at the present time either or both of these concepts explain parturition in all species, but by examining a number of different species we hope to illustrate as many of the discrepancies as similarities.

Endocrine control of parturition

THERAPEUTIC ABORTION USING PROSTAGLANDIN F2α

Aspirin and Indomethacin Prolong Parturition in Rats: Evidence that Prostaglandins Contribute to Expulsion of Foetus

S. M. M. Karim

Papers

INDUCTION OF LABOUR WITH PROSTAGLANDIN F2α

EFFECTS OF PROSTAGLANDINS E1, E2, F1α, F2α ON ISOLATED HUMAN UMBILICAL AND PLACENTAL BLOOD VESSELS